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Update AIX FAQ:

Browse Source 
At any rate, here's a revision to CVS HEAD to reflect some changes by
myself and by Seneca Cunningham for the AIX FAQ.  It touches on the
following issues:

1.  memcpy pointer patch for dynahash.c

2.  AIX memory management, which can, for 32 bit cases, bite people
    quite unexpectedly...

Chris Browne
This commit is contained in:
Bruce Momjian 2006-04-13 11:41:02 +00:00
parent 9204980aa1
commit 98c6c966bc
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doc/FAQ_AIX
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@ -1,5 +1,5 @@
From: Zeugswetter Andreas <ZeugswetterA@spardat.at>
$Date: 2006/04/05 22:55:05 $
$Date: 2006/04/13 11:41:02 $
On AIX 4.3.2 PostgreSQL compiled with the native IBM compiler xlc
(vac.C 5.0.1) passes all regression tests. Other versions of OS and
@ -113,6 +113,68 @@ libraries, the following URLs may help you...
http://www.faqs.org/faqs/aix-faq/part4/section-22.html
http://www.han.de/~jum/aix/ldd.c
---
From: Christopher Browne <cbbrowne@ca.afilias.info>
Date: 2005-11-02
On AIX 5.3 ML3 (e.g. maintenance level 5300-03), there is some problem
with the handling of the pointer to memcpy. It is speculated that
this relates to some linker bug that may have been introduced between
5300-02 and 5300-03, but we have so far been unable to track down the
cause.
At any rate, the following patch, which "unwraps" the function
reference, has been observed to allow PG 8.1 pre-releases to pass
regression tests.
The same behaviour (albeit with varying underlying functions to
"blame") has been observed when compiling with either GCC 4.0 or IBM
XLC.
------------ per Seneca Cunningham -------------------
The following patch works on the AIX 5.3 ML3 box here and didn't cause
any problems with postgres on the x86 desktop. It's just a cleaner
version of what I tried earlier.
*** dynahash.c.orig Tue Nov 1 19:41:42 2005
--- dynahash.c Tue Nov 1 20:30:33 2005
***************
*** 670,676 ****
/* copy key into record */
currBucket->hashvalue = hashvalue;
! hashp->keycopy(ELEMENTKEY(currBucket), keyPtr, keysize);
/* caller is expected to fill the data field on return */
--- 670,687 ----
/* copy key into record */
currBucket->hashvalue = hashvalue;
! if (hashp->keycopy == memcpy)
! {
! memcpy(ELEMENTKEY(currBucket), keyPtr, keysize);
! }
! else if (hashp->keycopy == strncpy)
! {
! strncpy(ELEMENTKEY(currBucket), keyPtr, keysize);
! }
! else
! {
! hashp->keycopy(ELEMENTKEY(currBucket), keyPtr, keysize);
! }
/* caller is expected to fill the data field on return */
------------ per Seneca Cunningham -------------------
---
AIX, readline, and postgres 8.1.x:
@ -185,3 +247,121 @@ References
IBM Redbook
http://www.redbooks.ibm.com/redbooks/pdfs/sg245674.pdf
http://www.redbooks.ibm.com/abstracts/sg245674.html?Open
-----
AIX Memory Management: An Overview
==================================
by Seneca Cunningham...
AIX can be somewhat peculiar with regards to the way it does memory
management. You can have a server with many multiples of gigabytes of
RAM free, but still get out of memory or address space errors when
running applications.
Two examples of AIX-specific memory problems
--------------------------------------------
Both examples were from systems with gigabytes of free RAM.
a) createlang failing with unusual errors
Running as the owner of the postgres install:
-bash-3.00$ createlang plpgsql template1
createlang: language installation failed: ERROR: could not load library
"/opt/dbs/pgsql748/lib/plpgsql.so": A memory address is not in the
address space for the process.
Running as a non-owner in the group posessing the postgres install:
-bash-3.00$ createlang plpgsql template1
createlang: language installation failed: ERROR: could not load library
"/opt/dbs/pgsql748/lib/plpgsql.so": Bad address
b) out of memory errors in the postgres logs
Every memory allocation near or greater than 256MB failing.
The cause of these problems
----------------------------
The overall cause of all these problems is the default bittedness and
memory model used by the postmaster process.
By default, all binaries built on AIX are 32-bit. This does not
depend upon hardware type or kernel in use. These 32-bit processes
are limited to 4GB of memory laid out in 256MB segments using one of a
few models. The default allows for less than 256MB in the heap as it
shares a single segment with the stack.
In the case of example a), above, check your umask and the permissions
of the binaries in your postgres install. The binaries involved in
that example were 32-bit and installed as mode 750 instead of 755.
Due to the permissions being set in this fashion, only the owner or a
member of the possessing group can load the library. Since it isn't
world-readable, the loader places the object into the process' heap
instead of the shared library segments where it would otherwise be
placed.
Solutions and workarounds
-------------------------
In this section, all build flag syntax is presented for gcc.
The "ideal" solution for this is to use a 64-bit build of postgres,
but that's not always practical. Systems with 32-bit processors can
build, but not run, 64-bit binaries.
If a 32-bit binary is desired, set LDR_CNTRL to "MAXDATA=0xn0000000",
where 1 <= n <= 8, before starting the postmaster and try different
values and postgresql.conf settings to find a configuration that works
satisfactorily. This use of LDR_CNTRL tells AIX that you want the
postmaster to have $MAXDATA bytes set aside for the heap, allocated in
256MB segments.
When you find a workable configuration, ldedit can be used to modify
the binaries so that they default to using the desired heap size.
PostgreSQL might also be rebuilt, passing configure
LDFLAGS="-Wl,-bmaxdata:0xn0000000" to achieve the same effect.
For a 64-bit build, set OBJECT_MODE to 64 and pass CC="gcc -maix64"
and LDFLAGS="-Wl,-bbigtoc" to configure. If you omit the export of
OBJECT_MODE, your build may fail with linker errors. When OBJECT_MODE
is set, it tells AIX's build utilities such as ar, as, and ld what
type of objects to default to handling.
Overcommit
----------
By default, overcommit of paging space can happen. While I have not
seen this occur, AIX will kill processes when it runs out of memory
and the overcommit is accessed. The closest to this that I have seen
is fork failing because the system decided that there was not enough
memory for another process. Like many other parts of AIX, the paging
space allocation method and out-of-memory kill is configurable on a
system- or process-wide basis if this becomes a problem.
References and resources
------------------------
"Large Program Support"
AIX Documentation: General Programming Concepts: Writing and Debugging Programs
http://publib.boulder.ibm.com/infocenter/pseries/topic/com.ibm.aix.doc/aixprggd/genprogc/lrg_prg_support.htm
"Program Address Space Overview"
AIX Documentation: General Programming Concepts: Writing and Debugging Programs
http://publib.boulder.ibm.com/infocenter/pseries/topic/com.ibm.aix.doc/aixprggd/genprogc/address_space.htm
"Performance Overview of the Virtual Memory Manager (VMM)"
AIX Documentation: Performance Management Guide
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/topic/com.ibm.aix.doc/aixbman/prftungd/resmgmt2.htm
"Page Space Allocation"
AIX Documentation: Performance Management Guide
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/topic/com.ibm.aix.doc/aixbman/prftungd/memperf7.htm
"Paging-space thresholds tuning"
AIX Documentation: Performance Management Guide
http://publib.boulder.ibm.com/infocenter/pseries/v5r3/topic/com.ibm.aix.doc/aixbman/prftungd/memperf6.htm
"Developing and Porting C and C++ Applications on AIX"
IBM Redbook
http://www.redbooks.ibm.com/redbooks/pdfs/sg245674.pdf
http://www.redbooks.ibm.com/abstracts/sg245674.html?Open