Re: AIX FAQ

Patch applied. Thanks.

Backpatched to 8.1.X.

---------------------------------------------------------------------------

Chris Browne wrote:
> Some of this may have already made it in; it's not totally clear...
>
> 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...
>
> Index: FAQ_AIX
> ===================================================================
> RCS file: /projects/cvsroot/pgsql/doc/FAQ_AIX,v
> retrieving revision 1.16
> diff -c -r1.16 FAQ_AIX
> *** FAQ_AIX 5 Apr 2006 22:55:05 -0000 1.16
> --- FAQ_AIX 6 Apr 2006 20:07:28 -0000
> ***************
> *** 113,118 ****
> --- 113,180 ----
> http://www.faqs.org/faqs/aix-faq/part4/section-22.html
>
> http://www.han.de/~jum/aix/ldd.c
> +
> + ---
> + From: Christopher Browne <cbbrowne(at)ca(dot)afilias(dot)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:
> ***************
> *** 185,187 ****
> --- 247,367 ----
> 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
>
> --
> (reverse (concatenate 'string "gro.gultn" "@" "enworbbc"))
> http://www3.sympatico.ca/cbbrowne/linuxxian.html
> "What's wrong with 3rd party tools? Especially if they are free? What
> the **** do you think Unix is anyway? It's a big honkin' party of 3rd
> party free tools." -- Bob Cassidy (rmcassid(at)uci(dot)edu)
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster
>

--
Bruce Momjian http://candle.pha.pa.us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +