915 lines
36 KiB
Plaintext
915 lines
36 KiB
Plaintext
Frequently Asked Questions (FAQ) for Postgres95
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Last updated: Mon Oct 14 08:05:23 EDT 1996
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Version: 2.0
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Current maintainer: Bruce Momjian (maillist@candle.pha.pa.us)
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The most recent version of this document can be viewed at the postgres95 Web
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site, http://www.ki.net/postgres95.
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Linux-specific questions are answered in
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http://www.ki.net/postgres95/docs/FAQ-Linux.phtml.
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Irix-specific questions are answered in
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http://www.ki.net/postgres95/docs/FAQ-Irix.phtml.
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Changes in this version (* = modified, + = new):
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* *3.41) What is the meaning of some of the terms used in Postgres?
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----------------------------------------------------------------------------
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Questions answered:
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1) General questions
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1.1) What is Postgres95?
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1.2) What does Postgres95 run on?
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1.3) Where can I get Postgres95?
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1.4) What's the copyright on Postgres95?
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1.5) Support for Postgres95
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1.6) Latest release of Postgres95
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1.7) Is there a commercial version of Postgres95?
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1.9) What version of SQL does Postgres95 use?
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1.10) Does Postgres95 work with databases from earlier versions of postgres?
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1.11) How many people use Postgres95?
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2) Installation questions
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2.1) I get the error "cpp: command not found" when I try to compile
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2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
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2.3) initdb doesn't run
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2.4) when I start up the postmaster, I get
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2.5) The system seems to be confused about commas, decimal points, and date
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formats.
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2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
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2.7) The backend compiled successfully, but compiling libpq resulted in a
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complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
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2.8) Where can I find the bug fixes for postgres95?
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2.9) I can't apply the patches even though everything looks like it should
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work.
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2.10) When I run postmaster, I get a Bad System Call core dumped message.
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2.11) I get the error message "obj/fmgr.h: No such file or directory"
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2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
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2.13) I get the strange make errors right at the beginning:
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2.14) I have changed a source file, but a recompile does not see the change.
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3) Postgres95 Features questions
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3.1) How do I specify a KEY or other constraints on a column?
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3.2) Does Postgres95 support nested subqueries?
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3.3) How do I define a unique indices?
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3.4) I've having a lot of problems with using rules.
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3.5) I can't seem to write into the middle of large objects reliably.
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3.6) Does postgres95 have a graphical user interface? A report
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3.7) How can I write client applications to Postgres95?
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3.8) How do I prevent other hosts from accessing my Postgres95
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3.9) How do I set up a pg_group?
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3.10) What is the exact difference between binary cursors and normal
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cursors?
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3.11) Why doesn't the != operator work?
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3.12) What is a R-tree index and what is it used for?
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3.13) What is the maximum size for a tuple?
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3.14) I defined indices but my queries don't seem to make use of them. Why?
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3.15) Are there ODBC drivers for Postgres95?
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3.16) How do I use postgres for multi-dimensional indexing (> 2 dimensions)?
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3.17) How do I do regular expression searches? case-insensitive regexp
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searching?
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3.18) I can't access the database as the 'root' user.
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3.19) I experienced a server crash during a vacuum. How do I remove the lock
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file?
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3.20) What is the difference between the various character types?
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3.21) In a query, how do I detect if a field is NULL?
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3.22) How do I see how the query optimizer is evaluating my query?
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3.23) How do I create a serial field?
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3.24) How do I create a multi-column index?
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3.25) What are the temp_XXX files in my database directory?
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3.26) Why are my table files not getting any smaller after a delete?
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3.27) Why can't I connect to my database from another machine?
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3.28) I get the error 'default index class unsupported' when creating an
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index. How do I do it?
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3.29) Why does creating an index crash the backend server?
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3.30) How do I specify a decimal constant as a float8, or a string as a
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text? Why am I getting poor precision?
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3.30) How do I specify a decimal constant as a float8, or a string as a
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text? Why am I getting poor precision?
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3.31) How do I find out what indexes or operations are defined in the
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database?
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3.32) My database is corrupt. I can't do anything. What should I do?
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3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
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3.34) Why does 'createuser' return 'unexpected last match in input()'?
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3.35) All my servers crash under concurrent table access. Why?
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3.36) What tools are available for hooking postgres to Web pages?
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3.37) What is the time-warp feature and how does it relate to vacuum?
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3.38) How do I tune the database engine for better performance?
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3.39) What debugging features are available in Postgres95?
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3.40) What is an oid? What is a tid?
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3.41) What is the meaning of some of the terms used in Postgres?
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4) Questions about extending Postgres95
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4.1) I wrote a user-defined function and when I run it in psql, it dumps
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core.
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4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0
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4.3) I've written some nifty new types and functions for Postgres95.
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4.4) How do I write a C function to return a tuple?
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5) Bugs
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5.1) How do I find out about bug fixes?
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5.2) How do I make a bug report?
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----------------------------------------------------------------------------
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Section 1: General Questions
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1.1) What is Postgres95?
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Postgres95 is an enhancement of the POSTGRES database management system, a
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next-generation DBMS research prototype. While Postgres95 retains the
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powerful data model and rich data types of POSTGRES, it replaces the
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PostQuel query language with an extended subset of SQL. Postgres95 is free
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and the complete source is available.
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Postgres95 development is being performed by a team of Internet developers
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who all subscribe to the Postgres95 development mailing list. The current
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coordinator is Marc G. Fournier (scrappy@ki.net). (See below on how to
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join). This team is now responsible for all current and future development
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of Postgres95.
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The authors of Postgres95 1.01 were Andrew Yu and Jolly Chen. Many others
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have contributed to the porting, testing, debugging and enhancement of the
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code. The original Postgres code, from which Postgres95 is derived, was the
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effort of many graduate students, undergraduate students, and staff
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programmers working under the direction of Professor Michael Stonebraker at
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the University of California, Berkeley.
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1.2) What does Postgres95 run on?
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The authors have compiled and tested Postgres95 on the following
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platforms(some of these compiles require gcc 2.7.0):
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* DEC Alpha AXP on OSF/1 2.0
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* HP PA-RISC on HP-UX 9.0
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* i386 Solaris
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* SUN SPARC on Solaris 2.4
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* SUN SPARC on SunOS 4.1.3
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* DEC MIPS on Ultrix 4.4
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* Intel x86 on Linux 1.2 and Linux ELF
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* OSs derived from 4.4-lite BSD (NetBSD, FreeBSD)
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* IBM on AIX 3.2.5
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* BSD/OS 2.0, 2.01 & 2.1
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* SGI MIPS on IRIX 5.3
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The following ports are bundled with the Postgres95 distribution. The
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authors do not have handy access to these platforms but the ports have been
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tested by the others.
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* Motorola MC68K or Intel x86 on NeXTSTEP 3.2
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* Intel x86 on Intel SVR4
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1.3) Where can I get Postgres95?
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The primary anonymous ftp site for postgres95 is:
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* ftp://ftp.ki.net/pub/postgres95
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A mirror site exists at:
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* ftp://postgres95.vnet.net/pub/postgres95
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* ftp://ftp.luga.or.at/pub/postgres95
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* ftp://cal011111.student.utwente.nl/pub/postgres95
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1.4) What's the copyright on Postgres95?
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Postgres95 is subject to the following COPYRIGHT.
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POSTGRES95 Data Base Management System
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Copyright (c) 1994-6 Regents of the University of California
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Permission to use, copy, modify, and distribute this software and its
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documentation for any purpose, without fee, and without a written agreement
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is hereby granted, provided that the above copyright notice and this
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paragraph and the following two paragraphs appear in all copies.
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IN NO EVENT SHALL THE UNIVERSITY OF CALIFORNIA BE LIABLE TO ANY PARTY FOR
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DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING
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LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION,
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EVEN IF THE UNIVERSITY OF CALIFORNIA HAS BEEN ADVISED OF THE POSSIBILITY OF
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SUCH DAMAGE.
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THE UNIVERSITY OF CALIFORNIA SPECIFICALLY DISCLAIMS ANY WARRANTIES,
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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN
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"AS IS" BASIS, AND THE UNIVERSITY OF CALIFORNIA HAS NO OBLIGATIONS TO
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PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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1.5) Support for Postgres95
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There is no official support for Postgres95 from the original maintainers or
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from University of California, Berkeley. It is maintained through volunteer
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effort only.
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With the generosity of the Jason Wright and others at Vnet, the postgres95
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mailing list now has a new home -- postgres95@postgres95.vnet.net. It is
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available for discussion of matters pertaining to Postgres95, including but
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not limited to bug reports and fixes. For info on how to subscribe, send a
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mail with the lines in the body (not the subject line)
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help
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info postgres95
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to majordomo@postgres95.vnet.net.
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There is also a digest list available. To subscribe to this list, send email
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to majordomo@postgres95.vnet.net with a BODY of:
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subscribe postgres95-digest
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Digests are sent out to members of this list whenever the main list has
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received around 30k of messages.
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Archives and digests of the new mailing list at Vnet can be found at:
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* ftp://postgres95.vnet.net/pub/postgres95/archives
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* ftp://postgres95.vnet.net/pub/postgres95/digests
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There is also a developers mailing list available. To subscribe to this
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list, send email to pg95-dev-request@ki.net with a BODY of:
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subscribe pg95-dev
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Additional information about Postgres95 can be found via the postgres95 WWW
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home page at:
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http://www.ki.net/postgres95
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1.6) Latest release of Postgres95
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The latest release of postgres95 is version 1.08.
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1.7) Is there a commercial version of Postgres95?
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Illustra Information Technology (a wholly owned subsidiary of Informix
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Software, Inc.) sells an object-relational DBMS called Illustra that was
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originally based on postgres. Illustra has cosmetic similarities to
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postgres95 but has more features, is more robust, performs better, and
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offers real documentation and support. On the flip side, it costs money. For
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more information, contact sales@illustra.com
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1.8) What documentation is available for Postgres95?
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A user manual, manual pages, and some small test examples are included in
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the distribution. The sql and built-in manual pages are particularly
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important.
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The www page contains pointers to an implementation guide and five papers
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written about postgres design concepts and features.
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1.9) What version of SQL does Postgres95 use?
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Postgres95 supports a subset of SQL-92. It has most of the important
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constructs but lacks some of the functionality. The most visible differences
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are:
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* no support for primary keys or column constraints
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* no support for nested subqueries
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* no HAVING clause under a GROUP BY
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On the other hand, you get to create user-defined types, functions,
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inheritance etc. If you're willing to help with postgres95 coding,
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eventually we can also add the missing features listed above.
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1.10) Does Postgres95 work with databases from earlier versions of postgres?
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Postgres95 v1.08 is compatible with databases created with v1.01. Those
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upgrading from 1.0 should read the directions in the MIGRATION_1.0_TO_1.02
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directory.
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1.11) How many people use Postgres95?
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Since we don't have any licensing or registration scheme, it's impossible to
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tell. We do know hundreds copies of postgres95 v1.* have been downloaded,
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and that there many hundreds of subscribers to the mailing lists.
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----------------------------------------------------------------------------
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Section 2: Installation Questions
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2.1) I get the error "cpp: command not found" when I try to compile the
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backend.
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Edit the src/backend/utils/Gen_fmgrtab.sh script to include the path for the
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cpp for your particular site.
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2.2) I get 'yy_flush_buffer undefined' when I try to compile the backend
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Use a more recent version of flex, version 2.5.2. Version 2.5.3 has a known
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bug.
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2.3) initdb doesn't run
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* check to see that you have the proper paths set
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* check that the 'postgres' user owns all the right files
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* ensure that there are files in $PGDATA/files, and that they are
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non-empty. If they aren't, then "gmake install" failed for some reason
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2.4) when I start up the postmaster, I get "FindBackend: could not find a
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backend to execute..." "postmaster: could not find backend to execute..."
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You probably do not have the right path set up. The 'postgres' executable
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needs to be in your path.
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2.5) The system seems to be confused about commas, decimal points, and date
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formats.
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Check your locale configuration. postgres95 uses the locale settings of the
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user that ran the postmaster process. Set those accordingly for your
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operating environment.
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2.6) How do I install postgres95 somewhere other than /usr/local/postgres95?
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You need to manually edit the paths in src/Makefile.global to your site
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configuration.
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2.7) The backend compiled successfully, but compiling libpq resulted in a
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complaint: "libpq/pqcomm.h" not found when compiling fe-auth.c.
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You've probably installed postgres95 somewhere other than
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/usr/local/postgres, but didn't edit the src/Makefile.global accordingly.
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See question 2.6.
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2.8) Where can I find the bug fixes for postgres95?
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The patches should be applied in the order listed. The patch files can be
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ftp'ed directly from the directory:
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* ftp://ftp.ki.net/pub/postgres95
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2.9) I can't apply the patches even though everything looks like it should
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work.
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If you cut and paste directly off your web browser, tabs and whitespaces may
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not be preserved properly. Use the 'save as file' option from your web
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browser instead.
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2.10) When I run postmaster, I get a Bad System Call core dumped message.
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It could be a variety of problems, but first check to see that you have
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system V extensions installed on your kernel. Postgres95 requires kernel
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support for shared memory.
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2.11) I get the error message "obj/fmgr.h: No such file or directory"
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This indicates that you did not generate the file fmgr.h properly. Something
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failed in the running of the src/backend/utils/Gen_fmgrtab.sh script. Check
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to see the paths used in that script is appropriate to your system.
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2.12) When I try to start the postmaster, I get IpcMemoryCreate errors.
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You either do not have shared memory configured properly in kernel or you
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need to enlarge the shared memory available in the kernel. The exact amount
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you need depends on your architecture and how many buffers you configure
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postmaster to run with. For most systems, with default buffer sizes, you
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need a minimum of ~760K.
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2.13) I get the strange make errors right at the beginning:
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warning: NUL character seen; rest of line ignored
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*** missing separator. Stop.
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or
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Is a directory. Stop.
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Eliminate any whitespaces at the end of the PORTNAME line in
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Makefile.global. Extraneous tabs or spaces will confuse the make templates.
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2.14) I have changed a source file, but a recompile does not see the change?
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The Makefiles do not have the proper dependencies. You have to do a 'make
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clean' and then another 'make'.
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----------------------------------------------------------------------------
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Section 3: Postgres95 Features
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3.1) How do I specify a KEY or other constraints on a column?
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Column constraints are not supported in postgres95. As a consequence, the
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system does not check for duplicates.
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3.2) Does Postgres95 support nested subqueries?
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Subqueries are not implemented, but they can be simulated using sql
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functions.
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3.3) How do I define a unique indices?
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Postgres95 does not support unique indices. Defining an index does not
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preclude insertion of duplicate index key values.
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3.4) I've having a lot of problems with using rules.
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Currently, the rule system in postgres95 is mostly broken. It works enough
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to support the view mechanism, but that's about it. Use postgres95 rules at
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your own peril.
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3.5) I can't seem to write into the middle of large objects reliably.
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The Inversion large object system in postgres95 is also mostly broken. It
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works well enough for storing large wads of data and reading them back out,
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but the implementation has some underlying problems. Use postgres95 large
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objects at your own peril.
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3.6) Does postgres95 have a graphical user interface? A report generator? A
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embedded query language interface?
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No. No. No. Not in the official distribution at least. Some users have
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reported some success at using 'pgbrowse' and 'onyx' as frontends to
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postgres95. Several contributions are working on tk based frontend tools.
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Ask on the mailing list.
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3.7) How can I write client applications to Postgres95?
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Postgres95 supports a C-callable library interface called libpq as well as a
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Tcl-based library interface called libtcl.
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Others have contributed a perl interface and a WWW gateway to postgres95.
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See the postgres95 home pages for more details.
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3.8) How do I prevent other hosts from accessing my Postgres95 backend?
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Use host-based authentication by modifying the file $PGDATA/pg_hba
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accordingly.
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3.9) How do I set up a pg_group?
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Currently, there is no easy interface to set up user groups. You have to
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explicitly insert/update the pg_group table. For example:
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jolly=> insert into pg_group (groname, grosysid, grolist)
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jolly=> values ('posthackers', '1234', '{5443, 8261}');
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INSERT 548224
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jolly=> grant insert on foo to group posthackers;
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CHANGE
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jolly=>
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The fields in pg_group are:
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* groname: the group name. This a char16 and should be purely
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alphanumeric. Do not include underscores or other punctuation.
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* grosysid: the group id. This is an int4. This should be unique for each
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group.
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* grolist: the list of pg_user id's that belong in the group. This is an
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int4[].
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3.10) What is the exact difference between binary cursors and normal
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cursors?
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Normal cursors return data back in ASCII format. Since data is stored
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natively in binary format, the system must do a conversion to produce the
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ASCII format. In addition, ASCII formats are often large in size than binary
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format. Once the attributes come back in ASCII, often the client application
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then has to convert it to a binary format to manipulate it anyway.
|
|
|
|
Binary cursors give you back the data in the native binary representation.
|
|
Thus, binary cursors will tend to be a little faster since there's less
|
|
overhead of conversion.
|
|
|
|
However, ASCII is architectural neutral whereas binary representation can
|
|
differ between different machine architecture. Thus, if your client machine
|
|
uses a different representation than you server machine, getting back
|
|
attributes in binary format is probably not what you want. Also, if your
|
|
main purpose is displaying the data in ASCII, then getting it back in ASCII
|
|
will save you some effort on the client side.
|
|
|
|
3.11) Why doesn't the != operator work?
|
|
|
|
SQL specifies <> as the inequality operator, and that is what we have
|
|
defined for the built-in types. You are free, however, to extend postgres95
|
|
to include the != operator if you like.
|
|
|
|
3.12) What is a R-tree index and what is it used for?
|
|
|
|
An r-tree index is used for indexing spatial data. A hash index can't handle
|
|
range searches. A B-tree index only handles range searches in a single
|
|
dimension. R-tree's can handle multi-dimensional data. For example, if a
|
|
R-tree index can be built on an attribute of type 'point', the system can
|
|
more efficient answer queries like select all points within a bounding
|
|
rectangle.
|
|
|
|
The canonical paper that describes the original R-Tree design is:
|
|
|
|
Guttman, A. "R-Trees: A Dynamic Index Structure for Spatial Searching." Proc
|
|
of the 1984 ACM SIGMOD Int'l Conf on Mgmt of Data, 45-57.
|
|
|
|
You can also find this paper in Stonebraker's "Readings in Database Systems"
|
|
|
|
3.13) What is the maximum size for a tuple?
|
|
|
|
Tuples are limited to 8K bytes. Taking into account system attributes and
|
|
other overhead, one should stay well shy of 8,000 bytes to be on the safe
|
|
side. To use attributes larger than 8K, try using the large objects
|
|
interface.
|
|
|
|
Tuples do not cross 8k boundaries so a 5k tuple will require 8k of storage.
|
|
|
|
3.14) I defined indices but my queries don't seem to make use of them. Why?
|
|
|
|
Postgres95 does not automatically maintain statistics. One has to make an
|
|
explicit 'vacuum' call to update the statistics. After statistics are
|
|
updated, the optimizer has a better shot at using indices. Note that the
|
|
optimizer is limited and does not use indices in some circumstances (such as
|
|
OR clauses).
|
|
|
|
If the system still does not see the index, it is probably because you have
|
|
created an index on a field with the improper *_ops type. For example, you
|
|
have created a CHAR(4) field, but have specified a char_ops index
|
|
type_class.
|
|
|
|
See the create_index manual page for information on what type classes are
|
|
available. It must match the field type.
|
|
|
|
Postgres does not warn the user when the improper index is created.
|
|
|
|
Indexes not used for ORDER BY operations.
|
|
|
|
3.15) Are there ODBC drivers for Postgres95?
|
|
|
|
There are two ODBC drivers available, PostODBC and OpenLink ODBC.
|
|
|
|
For all people being interested in PostODBC, there are now two mailing lists
|
|
devoted to the discussion of PostODBC. The mailing lists are:
|
|
|
|
* postodbc-users@listserv.direct. net
|
|
* postodbc-developers@listse rv.direct.net
|
|
|
|
these lists are ordinary majordomo mailing lists. You can subscribe by
|
|
sending a mail to:
|
|
|
|
* majordomo@listserv.direct.net
|
|
|
|
OpenLink ODBC is currently in beta under Linux. You can get it from
|
|
http://www.openlinksw.com/postgres.html. It works with our standard ODBC
|
|
client software so you'll have Postgres ODBC available on every client
|
|
platform we support (Win, Mac, Unix, VMS).
|
|
|
|
We will probably be selling this product to people who need
|
|
commercial-quality support, but a freeware version will always be available.
|
|
Questions to postgres95@openlink.co.uk.
|
|
|
|
3.16) How do I use postgres for multi-dimensional indexing (> 2
|
|
dimensions">)?
|
|
|
|
Builtin R-Trees can handle polygons and boxes. In theory, R-trees can be
|
|
extended to handle higher number of dimensions. In practice, extending
|
|
R-trees require a bit of work and we don't currently have any documentation
|
|
on how to do it.
|
|
|
|
3.17) How do I do regular expression searches? case-insensitive regexp
|
|
searching?
|
|
|
|
Postgres95 supports the SQL LIKE syntax as well as more general regular
|
|
expression searching with the ~ operator. The !~ is the negated regexp
|
|
operator. ~* and !~* are the case-insensitive regular expression operators.
|
|
|
|
3.18) I can't access the database as the 'root' user.
|
|
|
|
You should not create database users with user id 0(root). They will be
|
|
unable to access the database. This is a security precaution because of the
|
|
ability of any user to dynamically link object modules into the database
|
|
engine.
|
|
|
|
3.19) I experienced a server crash during a vacuum. How do I remove the lock
|
|
file?
|
|
|
|
If the server crashes during a vacuum command, chances are it will leave a
|
|
lock file hanging around. Attempts to re-run the vacuum command result in
|
|
|
|
WARN:can't create lock file -- another vacuum cleaner running?
|
|
|
|
If you are sure that no vacuum is actually running, you can remove the file
|
|
called "pg_vlock" in your database directory (which is $PGDATA/base/)
|
|
|
|
3.20) What is the difference between the various character types?
|
|
|
|
Type Internal Name Notes
|
|
--------------------------------------------------
|
|
CHAR char 1 character }
|
|
CHAR2 char2 2 characters }
|
|
CHAR4 char4 4 characters } optimized for a fixed length
|
|
CHAR8 char8 8 characters }
|
|
CHAR16 char16 16 characters }
|
|
CHAR(#) bpchar blank padded to the specified fixed length
|
|
VARCHAR(#) varchar size specifies maximum length, no padding
|
|
TEXT text length limited only by maximum tuple length
|
|
BYTEA bytea variable-length array of bytes
|
|
|
|
Remember, you need to use the internal name when creating indexes on these
|
|
fields or when doing other internal operations.
|
|
|
|
The last four types above are "varlena" types (i.e. the first four bytes is
|
|
the length, followed by the data). CHAR(#) and VARCHAR(#) allocate the
|
|
maximum number of bytes no matter how much data is stored in the field. TEXT
|
|
and BYTEA are the only character types that have variable length on the
|
|
disk.
|
|
|
|
3.21) In a query, how do I detect if a field is NULL?
|
|
|
|
Postgres95 has two builtin keywords, "isnull" and "notnull" (note no
|
|
spaces). Version 1.05 and later and 2.* understand IS NULL and IS NOT NULL.
|
|
|
|
3.22) How do I see how the query optimizer is evaluating my query?
|
|
|
|
Place the word 'EXPLAIN' at the beginning of the query, for example:
|
|
|
|
EXPLAIN SELECT * FROM table1 WHERE age = 23;
|
|
|
|
3.23) How do I create a serial field?
|
|
|
|
Postgres does not allow the user to specifiy a user column as type SERIAL.
|
|
Instead, you can use each row's oid field as a unique value. However, if you
|
|
need to dump and reload the database, you need to be using postgres version
|
|
1.07 or later or 2.* with pgdump's -o option or COPY's WITH OIDS option to
|
|
preserver the oids.
|
|
|
|
Another valid way of doing this is to create a function:
|
|
|
|
|
|
create table my_oids (f1 int4);
|
|
insert into my_oids values (1);
|
|
create function new_oid () returns int4 as
|
|
'update my_oids set f1 = f1 + 1; select f1 from my_oids; '
|
|
language 'sql';
|
|
|
|
then:
|
|
|
|
create table my_stuff (my_key int4, value text);
|
|
insert into my_stuff values (new_oid(), 'hello');
|
|
|
|
However, keep in mind there is a race condition here where one server could
|
|
do the update, then another one do an update, and they both could select the
|
|
same new id. This statement should be performed within a transaction.
|
|
|
|
3.24) How do I create a multi-column index?
|
|
|
|
You can not directly create a multi-column index using create index. You
|
|
need to define a function which acts on the multiple columns, then use
|
|
create index with that function.
|
|
|
|
3.25) What are the temp_XXX files in my database directory?
|
|
|
|
They are temp_ files generated by the query executor. For example, if a sort
|
|
needs to be done to satisfy an ORDER BY, some temp files are generated as a
|
|
result of the sort.
|
|
|
|
If you have no transactions or sorts running at the time, it is safe to
|
|
delete the temp_ files.
|
|
|
|
3.26) Why are my table files not getting any smaller after a delete?
|
|
|
|
If you run vacuum, unused rows will be marked for reuse, but the file blocks
|
|
are not released. We could move the unused rows to the end of the file and
|
|
use ftruncate() to decrease the file size, but no one has implemented this
|
|
yet.
|
|
|
|
3.27) Why can't I connect to my database from another machine?
|
|
|
|
The default configuration allows only connections from tcp/ip host
|
|
localhost. You need to add a host entry to the file postgres95/data/pg_hba.
|
|
|
|
3.28) I get the error 'default index class unsupported' when creating an
|
|
index. How do I do it?
|
|
|
|
You probably used:
|
|
|
|
create index idx1 on person using btree (name);
|
|
|
|
Postgres95 indexes are extensible, and therefore you must specify a
|
|
class_type when creating an index. Read the manual page for create index
|
|
(called create_index). Version 2.0 will correct this deficiency.
|
|
|
|
3.29) Why does creating an index crash the backend server?
|
|
|
|
You have probably defined an incorrect *_ops type class for the field you
|
|
are indexing.
|
|
|
|
3.30) How do I specify a decimal constant as a float8, or a string as a
|
|
text? Why am I getting poor precision?
|
|
|
|
Use the :: operator. It is needed only when the default promotion rules
|
|
fail. i.e.:
|
|
|
|
insert into tab1 values (4.23::float8, '2343'::text)
|
|
|
|
The default floating-point constant is a float4 in releases prior to 1.05.
|
|
Later releases default to float8.
|
|
|
|
3.31) How do I find out what indexes or operations are defined in the
|
|
database?
|
|
|
|
Run the file postgres95/src/tutorial/syscat.source. It illustrates many of
|
|
the 'select's needed to get information out of the database system tables.
|
|
|
|
3.32) My database is corrupt. I can't do anything. What should I do?
|
|
|
|
The 1.02 release has a README file and utility that describes a possible
|
|
cause of the problem and a workaround. See the file
|
|
postgres95/contrib/zap_ltv/README for more information. Also please contact
|
|
the README author to help generate a complete fix for this bug.
|
|
|
|
This bug may be fixed in 1.02.
|
|
|
|
3.33) Createdb, destroydb, createuser,destroyuser don't run. Why?
|
|
|
|
Release 1.02 does not have this problem.
|
|
|
|
The 1.01 release of postgres95 uses a variable called PAGER to filter the
|
|
output of SELECT statements. Unfortunately, this PAGER is used even when the
|
|
standard output is not a terminal.
|
|
|
|
3.34) Why does 'createuser' return 'unexpected last match in input(">)'?
|
|
|
|
You have compile postgres with flex version 2.5.3. There is bug in this
|
|
version of flex. Use flex version 2.5.2 instead. There is a doc/README.flex
|
|
file which will properly patch the flex 2.5.3 source code.
|
|
|
|
3.35) All my servers crash under concurrent table access. Why?
|
|
|
|
This problem can be caused by a kernel that is not configured to support
|
|
semaphores.
|
|
|
|
3.36) What tools are available for hooking postgres to Web pages?
|
|
|
|
For web integration, PHP/FI is an excellent interface. The URL for that is
|
|
http://www.vex.net/php/
|
|
|
|
PHP is great for simple stuff, but for more complex stuff, some still use
|
|
the perl interface and CGI.pm.
|
|
|
|
An example of using WWW with C to talk to Postgres is can be tried at:
|
|
|
|
* http://www.ki.net/~mlc
|
|
|
|
An WWW gatway based on WDB using perl can be downloaded from:
|
|
|
|
* http://www.eol.ists.ca/~dunlop/wdb -p95
|
|
|
|
3.37) What is the time-warp feature and how does it relate to vacuum?
|
|
|
|
Postgres95 handles data changes differently than most database systems. When
|
|
a row is changed in a table, the original row is marked with the time it was
|
|
changed, and a new row is created with the current data. By default, only
|
|
current rows are used in a table. If you specify a date/time after the table
|
|
name in a FROM clause, you can access the data that was current at that
|
|
time, i.e.
|
|
|
|
SELECT *
|
|
FROM employees ['July 24, 1996 09:00:00']
|
|
|
|
displays employee rows in the table at the specified time. You can specify
|
|
intervals like [date,date], [date,], [,date], or [,]. This last option
|
|
accesses all rows that ever existed.
|
|
|
|
INSERTed rows get a timestamp too, so rows that were not in the table at the
|
|
desired time will not appear.
|
|
|
|
Vacuum removes rows that are no longer current. This time-warp feature is
|
|
used by the engine for rollback and crash recovery. Expiration times can be
|
|
set with purge.
|
|
|
|
3.38) How do I tune the database engine for better performance?
|
|
|
|
There are two things that can be done. You can use Openlink's option to
|
|
disable fsync() by starting the postmaster with a '-o -F' option. This will
|
|
prevent fsync()'s from flushing to disk after every transaction.
|
|
|
|
You can also use the postmaster -B option to increase the number of shared
|
|
memory buffers shared among the backend processes. If you make this
|
|
parameter too high, the process will not start or crash unexpectedly. Each
|
|
buffer is 8K and the defualt is 64 buffers.
|
|
|
|
3.39) What debugging features are available in Postgres95?
|
|
|
|
Postgres95 has several features that report status information that can be
|
|
valuable for debugging purposes.
|
|
|
|
First, by compiling with DEBUG defined, many assert()'s monitor the progress
|
|
of the backend and halt the program when something unexpected occurs.
|
|
|
|
Both postmaster and postgres have several debug options available. First,
|
|
whenever you start the postmaster, make sure you send the standard output
|
|
and error to a log file, like:
|
|
|
|
cd /usr/local/postgres95
|
|
./bin/postmaster >server.log 2>&1 &
|
|
|
|
This will put a server.log file in the top-level postgres95 directory. This
|
|
file can contain useful information about problems or errors encountered by
|
|
the server. Postmaster has a -d option that allows even more detailed
|
|
information to be reported. The -d option takes a number 1-3 that specifies
|
|
the debug level. The query plans in a verbose debug file can be formatted
|
|
using the 'indent' program. (You may need to remove the '====' lines.) Be
|
|
warned that a debug level greater than one generates large log files.
|
|
|
|
You can actuall run the postgres backend from the command line, and type
|
|
your SQL statement directly. This is recommended ONLY for debugging
|
|
purposes. Note that a newline terminates the query, not a semicolon. If you
|
|
have compiled with debugging symbols, you can perhaps use a debugger to see
|
|
what is happening. Because the backend was not started from the postmaster,
|
|
it is not running in an identical environment and locking/backend
|
|
interaction problems may not be duplicated. Some operating system can attach
|
|
to a running backend directly to diagnose problems.
|
|
|
|
The postgres program has a -s, -A, -t options that can be very usefull for
|
|
debugging and performance measurements.
|
|
|
|
The EXPLAIN command (see this FAQ) allows you to see how postgres95 is
|
|
iterpreting your query.
|
|
|
|
3.40) What is an oid? What is a tid?
|
|
|
|
Oids are Postgres's answer to unique row ids or serial columns. Every row
|
|
that is created in Postgres gets a unique oid. All oids generated by initdb
|
|
are less than 16384 (from backend/access/transam.h). All post-initdb
|
|
(user-created) oids are equal or greater that this. All these oids are
|
|
unique not only within a table, or database, but unique within the entire
|
|
postgres installation.
|
|
|
|
Postgres uses oids in its internal system tables to link rows in separate
|
|
tables. These oids can be used to identify specific user rows and used in
|
|
joins. It is recommended you use column type oid to store oid values. See
|
|
the sql(l) manual page to see the other internal columns.
|
|
|
|
Tids are used to indentify specific physical rows with block and offset
|
|
values. Tids change after rows are modified or reloaded. They are used by
|
|
index entries to point to physical rows. They can not be accessed through
|
|
sql.
|
|
|
|
3.41) What is the meaning of some of the terms used in Postgres?
|
|
|
|
Some of the source code and older documentation use terms that have more
|
|
common usage. Here are some:
|
|
|
|
* row, record, tuple
|
|
* attribute, field, column
|
|
* table, class
|
|
* retrieve, select
|
|
* replace, update
|
|
* oid, serial value
|
|
* portal, cursor
|
|
* range variable, table name, table alias
|
|
|
|
Please let me know if you think of any more.
|
|
|
|
----------------------------------------------------------------------------
|
|
|
|
Section 4: Extending Postgres95
|
|
|
|
4.1) I wrote a user-defined function and when I run it in psql, it dumps
|
|
core.
|
|
|
|
The problem could be a number of things. Try testing your user-defined
|
|
function in a stand alone test program first. Also, make sure you are not
|
|
sending elog NOTICES when the front-end is expecting data, such as during a
|
|
type_in() or type_out() functions
|
|
|
|
4.2) I get messages of the type NOTICE:PortalHeapMemoryFree: 0x402251d0 not
|
|
in alloc set!
|
|
|
|
You are pfree'ing something that was not palloc'ed. When writing
|
|
user-defined functions, do not include the file "libpq-fe.h". Doing so will
|
|
cause your palloc to be a malloc instead of a free. Then, when the backend
|
|
pfrees the storage, you get the notice message.
|
|
|
|
4.3) I've written some nifty new types and functions for Postgres95.
|
|
|
|
Please share them with other postgres95 users. Send your extensions to
|
|
mailing list, and they will eventually end up in the contrib/ subdirectory.
|
|
|
|
4.4) How do I write a C function to return a tuple?
|
|
|
|
This requires extreme wizardry, so extreme that the authors have not ever
|
|
tried it, though in principle it can be done. The short answer is ... you
|
|
can't. This capability is forthcoming in the future.
|
|
|
|
----------------------------------------------------------------------------
|
|
|
|
Section 5: Bugs
|
|
|
|
5.1) How do I find out about bug fixes?
|
|
|
|
The directory ftp://ftp.ki.net/pub/postgres95 contains patches for the
|
|
latest release.
|
|
|
|
5.2) How do I make a bug report?
|
|
|
|
First, check to see that your bug is not one that has already been fixed
|
|
(question 5.1). Then, fill out the "bug-template" file and send it to:
|
|
|
|
* pg95-dev@ki.net
|
|
|
|
This is the address of the developers mailing list.
|