mirror of https://github.com/postgres/postgres
Update FAQ.
This commit is contained in:
Bruce Momjian
parent
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commit
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101
doc/FAQ
101
doc/FAQ
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@ -90,10 +90,10 @@
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4.14) In a query, how do I detect if a field is NULL?
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4.15) What is the difference between the various character types?
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4.16.1) How do I create a serial/auto-incrementing field?
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4.16.2) How do I get the value of a serial insert?
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4.16.2) How do I get the value of a SERIAL insert?
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4.16.3) Don't currval() and nextval() lead to a race condition with
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other concurrent backend processes?
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4.17) What is an oid? What is a tid?
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other users?
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4.17) What is an OID? What is a TID?
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4.18) What is the meaning of some of the terms used in PostgreSQL?
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4.19) Why do I get the error "FATAL: palloc failure: memory
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exhausted?"
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@ -108,13 +108,13 @@
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5.1) I wrote a user-defined function. When I run it in psql, why does
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it dump core?
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5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0
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not in alloc set! mean?
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0
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not in alloc set!" mean?
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5.3) How can I contribute some nifty new types and functions to
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PostgreSQL?
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5.4) How do I write a C function to return a tuple?
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5.5) I have changed a source file. Why does the recompile does not see
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the change?
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5.5) I have changed a source file. Why does the recompile not see the
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change?
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_________________________________________________________________
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General Questions
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@ -219,8 +219,8 @@
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The main mailing list is: pgsql-general@PostgreSQL.org. It is
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available for discussion of matters pertaining to PostgreSQL. To
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subscribe, send a mail with the lines in the body (not the subject
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||||
line)
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subscribe, send mail with the following lines in the body (not the
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subject line)
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subscribe
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end
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@ -280,8 +280,8 @@
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1.9) How do I find out about known bugs or missing features?
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PostgreSQL supports an extended subset of SQL-92. See our TODO for a
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list of known bugs, missing features, and future plans.
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PostgreSQL supports an extended subset of SQL-92. See our TODO list
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for known bugs, missing features, and future plans.
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1.10) How can I learn SQL?
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@ -303,16 +303,16 @@
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1.12) How do I join the development team?
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First, download the latest sources and read the PostgreSQL Developers
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First, download the latest source and read the PostgreSQL Developers
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documentation on our web site, or in the distribution. Second,
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subscribe to the pgsql-hackers and pgsql-patches mailing lists. Third,
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submit high-quality patches to pgsql-patches.
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There are about a dozen people who have commit privileges to the
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PostgreSQL CVS archive. They each have submitted so many high-quality
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patches that it was a pain for the existing committers to keep up, and
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we had confidence that patches they committed were likely to be of
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high quality.
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patches that it was impossible for the existing committers to keep up,
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and we had confidence that patches they committed were of high
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quality.
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1.13) How do I submit a bug report?
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@ -333,7 +333,7 @@
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some features they don't have, like user-defined types,
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inheritance, rules, and multi-version concurrency control to
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reduce lock contention. We don't have outer joins, but are
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working on them for our next release.
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working on them.
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Performance
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PostgreSQL runs in two modes. Normal fsync mode flushes every
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@ -442,7 +442,7 @@
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* Python(PyGreSQL)
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* TCL(libpgtcl)
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* C Easy API(libpgeasy)
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* Embedded HTML(PHP from http://www.php.net)
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* Embedded HTML (PHP from http://www.php.net)
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_________________________________________________________________
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Administrative Questions
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@ -474,9 +474,9 @@
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You either do not have shared memory configured properly in your
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kernel or you need to enlarge the shared memory available in the
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kernel. The exact amount you need depends on your architecture and how
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many buffers and backend processes you configure postmaster to run
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with. For most systems, with default numbers of buffers and processes,
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you need a minimum of ~1MB.
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many buffers and backend processes you configure for the postmaster.
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For most systems, with default numbers of buffers and processes, you
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need a minimum of ~1MB.
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3.5) When I try to start the postmaster, I get IpcSemaphoreCreate errors.
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Why?
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@ -511,7 +511,7 @@
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You should not create database users with user id 0 (root). They will
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be unable to access the database. This is a security precaution
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because of the ability of any user to dynamically link object modules
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because of the ability of users to dynamically link object modules
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into the database engine.
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3.9) All my servers crash under concurrent table access. Why?
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@ -533,9 +533,9 @@
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reduces the transaction overhead. Also consider dropping and
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recreating indices when making large data changes.
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There are several tuning things that can be done. You can disable
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fsync() by starting the postmaster with a -o -F option. This will
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prevent fsync()'s from flushing to disk after every transaction.
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There are several tuning options. You can disable fsync() by starting
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the postmaster with a -o -F option. This will prevent fsync()'s from
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flushing to disk after every transaction.
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You can also use the postmaster -B option to increase the number of
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shared memory buffers used by the backend processes. If you make this
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@ -548,7 +548,7 @@
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value is measured in kilobytes, and the default is 512 (ie, 512K).
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You can also use the CLUSTER command to group data in tables to match
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an index. See the cluster(l) manual page for more details.
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an index. See the CLUSTER manual page for more details.
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3.11) What debugging features are available?
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@ -629,8 +629,8 @@
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They are temporary files generated by the query executor. For example,
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if a sort needs to be done to satisfy an ORDER BY, and the sort
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requires more space than the backend's -S parameter allows, then temp
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files are created to hold the extra data.
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requires more space than the backend's -S parameter allows, then
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temporary files are created to hold the extra data.
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The temp files should be deleted automatically, but might not if a
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backend crashes during a sort. If you have no backends running at the
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@ -695,7 +695,7 @@ Maximum number of indexes on a table? unlimited
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BLCKSZ. To use attributes larger than 8K, you can also use the large
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object interface.
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Row length limit will be removed in 7.1.
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The row length limit will be removed in 7.1.
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4.7)How much database disk space is required to store data from a typical
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text file?
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@ -847,13 +847,13 @@ BYTEA bytea variable-length array of bytes
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CREATE UNIQUE INDEX person_id_key ON person ( id );
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See the create_sequence manual page for more information about
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sequences. You can also use each row's oid field as a unique value.
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sequences. You can also use each row's OID field as a unique value.
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However, if you need to dump and reload the database, you need to use
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pg_dump's -o option or COPY WITH OIDS option to preserve the oids.
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pg_dump's -o option or COPY WITH OIDS option to preserve the OIDs.
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Numbering Rows.
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4.16.2) How do I get the back the generated SERIAL value after an insert?
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4.16.2) How do I get the value of a SERIAL insert?
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One approach is to to retrieve the next SERIAL value from the sequence
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object with the nextval() function before inserting and then insert it
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@ -873,35 +873,35 @@ BYTEA bytea variable-length array of bytes
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INSERT INTO person (name) VALUES ('Blaise Pascal');
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$newID = currval('person_id_seq');
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Finally, you could use the oid returned from the INSERT statement to
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Finally, you could use the OID returned from the INSERT statement to
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lookup the default value, though this is probably the least portable
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approach. In perl, using DBI with Edmund Mergl's DBD::Pg module, the
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oid value is made available via $sth->{pg_oid_status} after
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$sth->execute().
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4.16.3) Don't currval() and nextval() lead to a race condition with other
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concurrent backend processes?
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users?
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No. This is handled by the backends.
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4.17) What is an oid? What is a tid?
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4.17) What is an OID? What is a TID?
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OIDs are PostgreSQL's answer to unique row ids. Every row that is
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created in PostgreSQL gets a unique oid. All oids generated during
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created in PostgreSQL gets a unique OID. All OIDs generated during
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initdb are less than 16384 (from backend/access/transam.h). All
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user-created oids are equal or greater that this. By default, all
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these oids are unique not only within a table, or database, but unique
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user-created OIDs are equal or greater that this. By default, all
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these OIDs are unique not only within a table, or database, but unique
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within the entire PostgreSQL installation.
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PostgreSQL uses oids in its internal system tables to link rows
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between tables. These oids can be used to identify specific user rows
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and used in joins. It is recommended you use column type oid to store
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oid values. You can create an index on the oid field for faster
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PostgreSQL uses OIDs in its internal system tables to link rows
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between tables. These OIDs can be used to identify specific user rows
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and used in joins. It is recommended you use column type OID to store
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OID values. You can create an index on the OID field for faster
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access.
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Oids are assigned to all new rows from a central area that is used by
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all databases. If you want to change the oid to something else, or if
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you want to make a copy of the table, with the original oid's, there
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all databases. If you want to change the OID to something else, or if
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you want to make a copy of the table, with the original OID's, there
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is no reason you can't do it:
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CREATE TABLE new_table(old_oid oid, mycol int);
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SELECT old_oid, mycol INTO new FROM old;
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@ -909,7 +909,7 @@ BYTEA bytea variable-length array of bytes
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DELETE FROM new;
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COPY new WITH OIDS FROM '/tmp/pgtable';
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Tids are used to identify specific physical rows with block and offset
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TIDs are used to identify specific physical rows with block and offset
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values. Tids change after rows are modified or reloaded. They are used
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by index entries to point to physical rows.
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@ -923,7 +923,7 @@ BYTEA bytea variable-length array of bytes
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* retrieve, select
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* replace, update
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* append, insert
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* oid, serial value
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* OID, serial value
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* portal, cursor
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* range variable, table name, table alias
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@ -969,7 +969,7 @@ BYTEA bytea variable-length array of bytes
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Currently, we join subqueries to outer queries by sequential scanning
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the result of the subquery for each row of the outer query. A
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workaround is to replace IN with EXISTS. For example, change:
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workaround is to replace IN with EXISTS:
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SELECT *
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FROM tab
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WHERE col1 IN (SELECT col2 FROM TAB2)
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@ -1005,8 +1005,8 @@ BYTEA bytea variable-length array of bytes
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The problem could be a number of things. Try testing your user-defined
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function in a stand alone test program first.
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5.2) What does the message: NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
|
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alloc set! mean?
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5.2) What does the message "NOTICE:PortalHeapMemoryFree: 0x402251d0 not in
|
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alloc set!" mean?
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You are pfree'ing something that was not palloc'ed. Beware of mixing
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malloc/free and palloc/pfree.
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@ -1021,9 +1021,8 @@ BYTEA bytea variable-length array of bytes
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This requires wizardry so extreme that the authors have never tried
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it, though in principle it can be done.
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5.5) I have changed a source file. Why does the recompile does not see the
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5.5) I have changed a source file. Why does the recompile not see the
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change?
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The Makefiles do not have the proper dependencies for include files.
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You have to do a make clean and then another make. You have to do a
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make clean and then another make.
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You have to do a make clean and then another make.
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|
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@ -64,12 +64,12 @@ with PostgreSQL?<BR>
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<A HREF="#3.1">3.1</A>) Why does <I>initdb</I> fail?<BR>
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<A HREF="#3.2">3.2</A>) How do I install PostgreSQL somewhere other than
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/usr/local/pgsql?<BR>
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<A HREF="#3.3">3.3</A>) When I start the postmaster, I get a
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<I>/usr/local/pgsql?</I><BR>
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<A HREF="#3.3">3.3</A>) When I start the <i>postmaster</i>, I get a
|
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<I>Bad System Call</I> or core dumped message. Why?<BR>
|
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<A HREF="#3.4">3.4</A>) When I try to start the postmaster, I get
|
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<A HREF="#3.4">3.4</A>) When I try to start the <i>postmaster</i>, I get
|
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<I>IpcMemoryCreate</I> errors. Why?<BR>
|
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<A HREF="#3.5">3.5</A>) When I try to start the postmaster, I get
|
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<A HREF="#3.5">3.5</A>) When I try to start the <i>postmaster</i>, I get
|
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<I>IpcSemaphoreCreate</I> errors. Why?<BR>
|
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<A HREF="#3.6">3.6</A>) How do I prevent other hosts from accessing my
|
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PostgreSQL database?<BR>
|
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@ -121,38 +121,40 @@ is NULL?<BR>
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<A HREF="#4.15">4.15</A>) What is the difference between the
|
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various character types?<BR>
|
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<A HREF="#4.16.1">4.16.1</A>) How do I create a serial/auto-incrementing field?<BR>
|
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<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a serial insert?<BR>
|
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<A HREF="#4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a
|
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race condition with other concurrent backend processes?<BR>
|
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<A HREF="#4.16.2">4.16.2</A>) How do I get the value of a
|
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<small>SERIAL</small> insert?<BR>
|
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<A HREF="#4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to a
|
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race condition with other users?<BR>
|
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|
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<A HREF="#4.17">4.17</A>) What is an oid? What is a tid?<BR>
|
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<A HREF="#4.17">4.17</A>) What is an <small>OID</small>? What is a
|
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<small>TID</small>?<BR>
|
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<A HREF="#4.18">4.18</A>) What is the meaning of some of the terms
|
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used in PostgreSQL?<BR>
|
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|
||||
<A HREF="#4.19">4.19</A>) Why do I get the error "FATAL: palloc
|
||||
failure: memory exhausted?"<BR>
|
||||
<A HREF="#4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
|
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failure: memory exhausted?"</I><BR>
|
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<A HREF="#4.20">4.20</A>) How do I tell what PostgreSQL version I
|
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am running? <BR>
|
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<A HREF="#4.21">4.21</A>) My large-object operations get <I>invalid
|
||||
large obj descriptor.</I> Why?<BR>
|
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<A HREF="#4.22">4.22</A>) How do I create a column that will default to the
|
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current time?<BR>
|
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<A HREF="#4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
|
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slow?<BR>
|
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<A HREF="#4.23">4.23</A>) Why are my subqueries using
|
||||
<CODE><small>IN</small></CODE> so slow?<BR>
|
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<A HREF="#4.24">4.24</A>) How do I do an <i>outer</i> join?<BR>
|
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|
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<H2><CENTER>Extending PostgreSQL</CENTER></H2>
|
||||
|
||||
<A HREF="#5.1">5.1</A>) I wrote a user-defined function. When I run
|
||||
it in <I>psql,</I> why does it dump core?<BR>
|
||||
<A HREF="#5.2">5.2</A>) What does the message:
|
||||
<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?<BR>
|
||||
<A HREF="#5.2">5.2</A>) What does the message
|
||||
<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?<BR>
|
||||
<A HREF="#5.3">5.3</A>) How can I contribute some nifty new types and functions
|
||||
to PostgreSQL?<BR>
|
||||
<A HREF="#5.4">5.4</A>) How do I write a C function to return a
|
||||
tuple?<BR>
|
||||
<A HREF="#5.5">5.5</A>) I have changed a source file. Why does the
|
||||
recompile does not see the change?<BR>
|
||||
recompile not see the change?<BR>
|
||||
|
||||
|
||||
<HR>
|
||||
|
|
@ -276,7 +278,7 @@ California, Berkeley. It is maintained through volunteer effort.<P>
|
|||
The main mailing list is: <A
|
||||
HREF="mailto:pgsql-general@PostgreSQL.org">pgsql-general@PostgreSQL.org</A>.
|
||||
It is available for discussion of matters pertaining to PostgreSQL.
|
||||
To subscribe, send a mail with the lines in the body (not
|
||||
To subscribe, send mail with the following lines in the body (not
|
||||
the subject line)
|
||||
|
||||
<PRE>
|
||||
|
|
@ -326,7 +328,7 @@ via the PostgreSQL WWW home page at:
|
|||
<A HREF="http://www.PostgreSQL.org">http://www.PostgreSQL.org</A>
|
||||
</BLOCKQUOTE><P>
|
||||
|
||||
There is also an IRC channel on EFNet, channel #PostgreSQL.
|
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There is also an IRC channel on EFNet, channel <I>#PostgreSQL.</I>
|
||||
I use the unix command <CODE>irc -c '#PostgreSQL' "$USER"
|
||||
irc.phoenix.net.</CODE><P>
|
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|
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|
|
@ -344,7 +346,7 @@ We plan to have major releases every four months.<P>
|
|||
<H4><A NAME="1.8">1.8</A>) What documentation is available?</H4><P>
|
||||
|
||||
Several manuals, manual pages, and some small test examples are
|
||||
included in the distribution. See the /doc directory. You can also
|
||||
included in the distribution. See the <I>/doc</I> directory. You can also
|
||||
browse the manual on-line at <A
|
||||
HREF="http://www.PostgreSQL.org/docs/postgres">
|
||||
http://www.PostgreSQL.org/docs/postgres</A>.
|
||||
|
|
@ -364,7 +366,7 @@ Our web site contains even more documentation.<P>
|
|||
|
||||
PostgreSQL supports an extended subset of SQL-92. See our
|
||||
<A HREF="http://www.PostgreSQL.org/docs/todo.html">
|
||||
TODO</A> for a list of known bugs, missing features, and future plans.<P>
|
||||
TODO</A> list for known bugs, missing features, and future plans.<P>
|
||||
|
||||
<H4><A NAME="1.10">1.10</A>) How can I learn SQL?</H4><P>
|
||||
|
||||
|
|
@ -394,16 +396,16 @@ Yes, we easily handle dates past the year 2000AD, and before 2000BC.<P>
|
|||
|
||||
<H4><A NAME="1.12">1.12</A>) How do I join the development team?</H4><P>
|
||||
|
||||
First, download the latest sources and read the PostgreSQL Developers
|
||||
First, download the latest source and read the PostgreSQL Developers
|
||||
documentation on our web site, or in the distribution.
|
||||
Second, subscribe to the pgsql-hackers and pgsql-patches mailing lists.
|
||||
Second, subscribe to the <I>pgsql-hackers</I> and <I>pgsql-patches</I> mailing lists.
|
||||
Third, submit high-quality patches to pgsql-patches.<P>
|
||||
|
||||
There are about a dozen people who have commit privileges to
|
||||
the PostgreSQL CVS archive. They each have submitted so many
|
||||
high-quality patches that it was a pain for the existing
|
||||
high-quality patches that it was impossible for the existing
|
||||
committers to keep up, and we had confidence that patches they
|
||||
committed were likely to be of high quality.
|
||||
committed were of high quality.
|
||||
|
||||
<H4><A NAME="1.13">1.13</A>) How do I submit a bug report?</H4><P>
|
||||
|
||||
|
|
@ -430,7 +432,7 @@ transactions, subselects, triggers, views, foreign key referential
|
|||
integrity, and sophisticated locking. We have some features they don't
|
||||
have, like user-defined types, inheritance, rules, and multi-version
|
||||
concurrency control to reduce lock contention. We don't have outer
|
||||
joins, but are working on them for our next release.<BR><BR>
|
||||
joins, but are working on them.<BR><BR>
|
||||
|
||||
<DT> <B>Performance</B>
|
||||
<DD>
|
||||
|
|
@ -560,7 +562,7 @@ We have:
|
|||
<LI>Python(PyGreSQL)
|
||||
<LI>TCL(libpgtcl)
|
||||
<LI>C Easy API(libpgeasy)
|
||||
<LI>Embedded HTML(<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
|
||||
<LI>Embedded HTML (<A HREF="http://www.php.net">PHP from http://www.php.net</A>)
|
||||
</UL><P>
|
||||
|
||||
<HR>
|
||||
|
|
@ -580,14 +582,14 @@ your path
|
|||
|
||||
|
||||
<H4><A NAME="3.2">3.2</A>) How do I install PostgreSQL somewhere
|
||||
other than /usr/local/pgsql?</H4><P>
|
||||
other than <I>/usr/local/pgsql?</I></H4><P>
|
||||
|
||||
The simplest way is to specify the --prefix option when running configure.
|
||||
If you forgot to do that, you can edit Makefile.global and change POSTGRESDIR
|
||||
accordingly, or create a Makefile.custom and define POSTGRESDIR there.<P>
|
||||
The simplest way is to specify the --prefix option when running <I>configure.</I>
|
||||
If you forgot to do that, you can edit <I>Makefile.global</I> and change POSTGRESDIR
|
||||
accordingly, or create a <I>Makefile.custom</I> and define POSTGRESDIR there.<P>
|
||||
|
||||
|
||||
<H4><A NAME="3.3">3.3</A>) When I start the postmaster, I get a <I>Bad
|
||||
<H4><A NAME="3.3">3.3</A>) When I start the <i>postmaster</i>, I get a <I>Bad
|
||||
System Call</I> or core dumped message. Why?</H4><P>
|
||||
|
||||
It could be a variety of problems, but first check to see that you
|
||||
|
|
@ -595,23 +597,23 @@ have System V extensions installed in your kernel. PostgreSQL requires
|
|||
kernel support for shared memory and semaphores.<P>
|
||||
|
||||
|
||||
<H4><A NAME="3.4">3.4</A>) When I try to start the postmaster, I
|
||||
<H4><A NAME="3.4">3.4</A>) When I try to start the <i>postmaster,</i> I
|
||||
get <I>IpcMemoryCreate</I> errors. Why?</H4><P>
|
||||
|
||||
You either do not have shared memory configured properly in your kernel or
|
||||
you need to enlarge the shared memory available in the kernel. The
|
||||
exact amount you need depends on your architecture and how many buffers
|
||||
and backend processes you configure postmaster to run with.
|
||||
and backend processes you configure for the <i>postmaster.</i>
|
||||
For most systems, with default numbers of buffers and processes, you
|
||||
need a minimum of ~1MB.<P>
|
||||
|
||||
<H4><A NAME="3.5">3.5</A>) When I try to start the postmaster, I
|
||||
<H4><A NAME="3.5">3.5</A>) When I try to start the <i>postmaster,</i> I
|
||||
get <I>IpcSemaphoreCreate</I> errors. Why?</H4><P>
|
||||
|
||||
If the error message is <I>IpcSemaphoreCreate: semget failed (No space
|
||||
left on device)</I> then your kernel is not configured with enough
|
||||
semaphores. Postgres needs one semaphore per potential backend process.
|
||||
A temporary solution is to start the postmaster with a smaller limit on
|
||||
A temporary solution is to start the <i>postmaster</i> with a smaller limit on
|
||||
the number of backend processes. Use <I>-N</I> with a parameter less
|
||||
than the default of 32. A more permanent solution is to increase your
|
||||
kernel's <SMALL>SEMMNS</SMALL> and <SMALL>SEMMNI</SMALL> parameters.<P>
|
||||
|
|
@ -635,7 +637,7 @@ another machine?</H4><P>
|
|||
|
||||
The default configuration allows only unix domain socket connections
|
||||
from the local machine. To enable TCP/IP connections, make sure the
|
||||
postmaster has been started with the <I>-i</I> option, and add an
|
||||
<i>postmaster</i> has been started with the <I>-i</I> option, and add an
|
||||
appropriate host entry to the file
|
||||
<I>pgsql/data/pg_hba.conf</I>.
|
||||
|
||||
|
|
@ -643,8 +645,8 @@ appropriate host entry to the file
|
|||
user?</H4><P>
|
||||
|
||||
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
|
||||
unable to access the database. This is a security precaution because
|
||||
of the ability of users to dynamically link object modules into the
|
||||
database engine.<P>
|
||||
|
||||
|
||||
|
|
@ -671,22 +673,23 @@ transaction block. This reduces the transaction overhead. Also
|
|||
consider dropping and recreating indices when making large data
|
||||
changes.<P>
|
||||
|
||||
There are several tuning things that can be done. You can disable
|
||||
<I>fsync()</I> by starting the postmaster with a <I>-o -F</I> option. This will
|
||||
prevent <I>fsync()'s</I> from flushing to disk after every transaction.<P>
|
||||
There are several tuning options. You can disable
|
||||
<I>fsync()</I> by starting the <I>postmaster</I> with a <I>-o -F</I>
|
||||
option. This will prevent <I>fsync()'s</I> from flushing to disk after
|
||||
every transaction.<P>
|
||||
|
||||
You can also use the postmaster -B option to increase the number of
|
||||
You can also use the <I>postmaster</I> <I>-B</I> option to increase the number of
|
||||
shared memory buffers used by the backend processes. If you make this
|
||||
parameter too high, the postmaster may not start because you've exceeded
|
||||
parameter too high, the <I>postmaster</I> may not start because you've exceeded
|
||||
your kernel's limit on shared memory space.
|
||||
Each buffer is 8K and the default is 64 buffers.<P>
|
||||
|
||||
You can also use the backend -S option to increase the maximum amount
|
||||
of memory used by the backend process for temporary sorts. The -S value
|
||||
You can also use the backend <I>-S</I> option to increase the maximum amount
|
||||
of memory used by the backend process for temporary sorts. The <I>-S</I> value
|
||||
is measured in kilobytes, and the default is 512 (ie, 512K).<P>
|
||||
|
||||
You can also use the <SMALL>CLUSTER</SMALL> command to group data in tables to
|
||||
match an index. See the cluster(l) manual page for more details.<P>
|
||||
match an index. See the <small>CLUSTER</small> manual page for more details.<P>
|
||||
|
||||
|
||||
<H4><A NAME="3.11">3.11</A>) What debugging features are available?</H4><P>
|
||||
|
|
@ -694,7 +697,7 @@ match an index. See the cluster(l) manual page for more details.<P>
|
|||
PostgreSQL has several features that report status information that can
|
||||
be valuable for debugging purposes.<P>
|
||||
|
||||
First, by running configure with the --enable-cassert option, many
|
||||
First, by running <I>configure</I> with the --enable-cassert option, many
|
||||
<I>assert()'s</I> monitor the progress of the backend and halt the program when
|
||||
something unexpected occurs.<P>
|
||||
|
||||
|
|
@ -708,7 +711,7 @@ standard output and error to a log file, like:
|
|||
|
||||
This will put a server.log file in the top-level PostgreSQL directory.
|
||||
This file contains useful information about problems or errors
|
||||
encountered by the server. <I>Postmaster</I> has a -d option that allows even
|
||||
encountered by the server. <I>Postmaster</I> has a <I>-d</I> option that allows even
|
||||
more detailed information to be reported. The <I>-d</I> option takes a number
|
||||
that specifies the debug level. Be warned that high debug level values
|
||||
generate large log files.<P>
|
||||
|
|
@ -743,19 +746,19 @@ in the client's current directory.<P>
|
|||
<H4><A NAME="3.12">3.12</A>) I get 'Sorry, too many clients' when trying
|
||||
to connect. Why?</H4><P>
|
||||
|
||||
You need to increase the postmaster's limit on how many concurrent backend
|
||||
You need to increase the <i>postmaster's</i> limit on how many concurrent backend
|
||||
processes it can start.<P>
|
||||
|
||||
In PostgreSQL 6.5 and up, the default limit is 32 processes. You can
|
||||
increase it by restarting the postmaster with a suitable <I>-N</I>
|
||||
increase it by restarting the <i>postmaster</i> with a suitable <I>-N</I>
|
||||
value. With the default configuration you can set <I>-N</I> as large as
|
||||
1024. If you need more, increase <SMALL>MAXBACKENDS</SMALL> in
|
||||
<I>include/config.h</I> and rebuild. You can set the default value of
|
||||
<I>-N</I> at configuration time, if you like, using configure's
|
||||
<I>-N</I> at configuration time, if you like, using <I>configure's</I>
|
||||
<I>--with-maxbackends</I> switch.<P>
|
||||
|
||||
Note that if you make <I>-N</I> larger than 32, you must also increase
|
||||
<I>-B</I> beyond its default of 64; -B must be at least twice -N, and
|
||||
<I>-B</I> beyond its default of 64; <I>-B</I> must be at least twice <I>-N,</I> and
|
||||
probably should be more than that for best performance. For large
|
||||
numbers of backend processes, you are also likely to find that you need
|
||||
to increase various Unix kernel configuration parameters. Things to
|
||||
|
|
@ -778,7 +781,7 @@ database directory?</H4><P>
|
|||
They are temporary files generated by the query executor. For
|
||||
example, if a sort needs to be done to satisfy an <SMALL>ORDER BY,</SMALL> and
|
||||
the sort requires more space than the backend's <I>-S</I> parameter allows,
|
||||
then temp files are created to hold the extra data.<P>
|
||||
then temporary files are created to hold the extra data.<P>
|
||||
|
||||
The temp files should be deleted automatically, but might not if a backend
|
||||
crashes during a sort. If you have no backends running at the time,
|
||||
|
|
@ -793,7 +796,7 @@ it is safe to delete the pg_tempNNN.NN files.<P>
|
|||
commas, decimal points, and date formats.</H4><P>
|
||||
|
||||
Check your locale configuration. PostgreSQL uses the locale setting of
|
||||
the user that ran the postmaster process. There are postgres and psql
|
||||
the user that ran the <i>postmaster</i> process. There are postgres and psql
|
||||
SET commands to control the date format. Set those accordingly for
|
||||
your operating environment.<P>
|
||||
|
||||
|
|
@ -862,7 +865,7 @@ To change the maximum row size, edit <I>include/config.h</I> and change
|
|||
<SMALL>BLCKSZ.</SMALL> To use attributes larger than 8K, you can also
|
||||
use the large object interface.<P>
|
||||
|
||||
Row length limit will be removed in 7.1.<P>
|
||||
The row length limit will be removed in 7.1.<P>
|
||||
|
||||
|
||||
<H4><A NAME="4.7">4.7</A>)How much database disk space is required to
|
||||
|
|
@ -1037,13 +1040,14 @@ is automatically translated into this:
|
|||
</PRE>
|
||||
See the <I>create_sequence</I> manual page for more information about sequences.
|
||||
|
||||
You can also use each row's <I>oid</I> field as a unique value. However, if
|
||||
You can also use each row's <I>OID</I> field as a unique value. However, if
|
||||
you need to dump and reload the database, you need to use <I>pg_dump's -o</I>
|
||||
option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the oids.<P>
|
||||
option or <SMALL>COPY WITH OIDS</SMALL> option to preserve the <small>OID</small>s.<P>
|
||||
|
||||
<A HREF="http://www.PostgreSQL.org/docs/aw_pgsql_book">Numbering Rows.</A>
|
||||
|
||||
<H4><A NAME="4.16.2">4.16.2</A>) How do I get the back the generated SERIAL value after an insert?</H4><P>
|
||||
<H4><A NAME="4.16.2">4.16.2</A>) How do I get the value of a
|
||||
<small>SERIAL</small> insert?</H4><P>
|
||||
One approach is to to retrieve the next SERIAL value from the sequence object with the <I>nextval()</I> function <I>before</I> inserting and then insert it explicitly. Using the example table in <A HREF="#4.16.1">4.16.1</A>, that might look like this:
|
||||
<PRE>
|
||||
$newSerialID = nextval('person_id_seq');
|
||||
|
|
@ -1056,35 +1060,37 @@ Alternatively, you could retrieve the just-assigned SERIAL value with the <I>cur
|
|||
INSERT INTO person (name) VALUES ('Blaise Pascal');
|
||||
$newID = currval('person_id_seq');
|
||||
</PRE>
|
||||
Finally, you could use the <A HREF="#4.17">oid</A> returned from the
|
||||
Finally, you could use the <A HREF="#4.17"><small>OID</small></A> returned from the
|
||||
INSERT statement to lookup the default value, though this is probably
|
||||
the least portable approach. In perl, using DBI with Edmund Mergl's
|
||||
DBD::Pg module, the oid value is made available via
|
||||
<I>$sth->{pg_oid_status} after $sth->execute().</I>
|
||||
|
||||
<H4><A NAME="4.16.3">4.16.3</A>) Don't currval() and nextval() lead to a race condition with other
|
||||
concurrent backend processes?</H4><P>
|
||||
<H4><A NAME="4.16.3">4.16.3</A>) Don't <I>currval()</I> and <I>nextval()</I> lead to
|
||||
a race condition with other users?</H4><P>
|
||||
|
||||
No. This is handled by the backends.
|
||||
|
||||
|
||||
<H4><A NAME="4.17">4.17</A>) What is an oid? What is a tid?</H4><P>
|
||||
<H4><A NAME="4.17">4.17</A>) What is an <small>OID</small>? What is a
|
||||
<small>TID</small>?</H4><P>
|
||||
|
||||
<small>OID</small>s are PostgreSQL's answer to unique row ids. Every row that is
|
||||
created in PostgreSQL gets a unique <small>oid</small>. All <small>oid</small>s generated during
|
||||
created in PostgreSQL gets a unique <small>OID</small>. All <small>OID</small>s generated during
|
||||
<I>initdb</I> are less than 16384 (from <I>backend/access/transam.h</I>). All
|
||||
user-created <small>oid</small>s are equal or greater that this. By default, all these
|
||||
<small>oid</small>s are unique not only within a table, or database, but unique within
|
||||
user-created <small>OID</small>s are equal or greater that this. By default, all these
|
||||
<small>OID</small>s are unique not only within a table, or database, but unique within
|
||||
the entire PostgreSQL installation.<P>
|
||||
|
||||
PostgreSQL uses <small>oid</small>s in its internal system tables to link rows between
|
||||
tables. These <small>oid</small>s can be used to identify specific user rows and used
|
||||
in joins. It is recommended you use column type <small>oid</small> to store <small>oid</small>
|
||||
values. You can create an index on the <small>oid</small> field for faster access.<P>
|
||||
PostgreSQL uses <small>OID</small>s in its internal system tables to link rows between
|
||||
tables. These <small>OID</small>s can be used to identify specific user rows and used
|
||||
in joins. It is recommended you use column type <small>OID</small> to
|
||||
store <small>OID</small>
|
||||
values. You can create an index on the <small>OID</small> field for faster access.<P>
|
||||
|
||||
<small>Oid</small>s are assigned to all new rows from a central area that is used by
|
||||
all databases. If you want to change the <small>oid</small> to something else, or if
|
||||
you want to make a copy of the table, with the original <small>oid</small>'s, there is
|
||||
O<small>id</small>s are assigned to all new rows from a central area that is used by
|
||||
all databases. If you want to change the <small>OID</small> to something else, or if
|
||||
you want to make a copy of the table, with the original <small>OID</small>'s, there is
|
||||
no reason you can't do it:
|
||||
|
||||
<PRE>
|
||||
|
|
@ -1099,7 +1105,7 @@ no reason you can't do it:
|
|||
-->
|
||||
</PRE><P>
|
||||
|
||||
Tids are used to identify specific physical rows with block and offset
|
||||
T<small>ID</small>s are used to identify 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.<P>
|
||||
|
||||
|
|
@ -1117,17 +1123,17 @@ common usage. Here are some:
|
|||
<LI> retrieve, select
|
||||
<LI> replace, update
|
||||
<LI> append, insert
|
||||
<LI> oid, serial value
|
||||
<LI> <small>OID</small>, serial value
|
||||
<LI> portal, cursor
|
||||
<LI> range variable, table name, table alias
|
||||
</UL><P>
|
||||
|
||||
<H4><A NAME="4.19">4.19</A>) Why do I get the error "FATAL: palloc
|
||||
failure: memory exhausted?"<BR></H4><P>
|
||||
<H4><A NAME="4.19">4.19</A>) Why do I get the error <I>"FATAL: palloc
|
||||
failure: memory exhausted?"</I><BR></H4><P>
|
||||
|
||||
It is possible you have run out of virtual memory on your system, or
|
||||
your kernel has a low limit for certain resources. Try this before
|
||||
starting the postmaster:
|
||||
starting the <i>postmaster:</i>
|
||||
|
||||
<PRE>
|
||||
ulimit -d 65536
|
||||
|
|
@ -1169,12 +1175,11 @@ Use <i>now()</i>:
|
|||
CREATE TABLE test (x int, modtime timestamp default now() );
|
||||
</PRE></CODE>
|
||||
<P>
|
||||
<H4><A NAME="4.23">4.23</A>) Why are my subqueries using <CODE>IN</CODE> so
|
||||
slow?<BR></H4><P>
|
||||
<H4><A NAME="4.23">4.23</A>) Why are my subqueries using
|
||||
<CODE><small>IN</small></CODE> so slow?<BR></H4><P>
|
||||
Currently, we join subqueries to outer queries by sequential scanning
|
||||
the result of the subquery for each row of the outer query. A workaround
|
||||
is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>. For example,
|
||||
change:
|
||||
is to replace <CODE>IN</CODE> with <CODE>EXISTS</CODE>:
|
||||
<CODE><PRE>
|
||||
SELECT *
|
||||
FROM tab
|
||||
|
|
@ -1215,8 +1220,8 @@ I run it in <I>psql,</I> why does it dump core?</H4><P>
|
|||
The problem could be a number of things. Try testing your user-defined
|
||||
function in a stand alone test program first.
|
||||
|
||||
<H4><A NAME="5.2">5.2</A>) What does the message:
|
||||
<I>NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!</I> mean?</H4><P>
|
||||
<H4><A NAME="5.2">5.2</A>) What does the message
|
||||
<I>"NOTICE:PortalHeapMemoryFree: 0x402251d0 not in alloc set!"</I> mean?</H4><P>
|
||||
|
||||
You are <I>pfree'ing</I> something that was not <I>palloc'ed.</I>
|
||||
Beware of mixing <I>malloc/free</I> and <I>palloc/pfree.</I>
|
||||
|
|
@ -1237,12 +1242,10 @@ This requires wizardry so extreme that the authors have never
|
|||
tried it, though in principle it can be done.<P>
|
||||
|
||||
<H4><A NAME="5.5">5.5</A>) I have changed a source file. Why does the
|
||||
recompile does not see the change?</H4><P>
|
||||
recompile not see the change?</H4><P>
|
||||
|
||||
The Makefiles do not have the proper dependencies for include files. You
|
||||
have to do a <I>make clean</I> and then another <I>make</I>.
|
||||
You
|
||||
have to do a <I>make clean</I> and then another <I>make.</I><P>
|
||||
The <I>Makefiles</I> do not have the proper dependencies for include files. You
|
||||
have to do a <I>make clean</I> and then another <I>make</I>.<P>
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</BODY>
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Reference in New Issue