From: Tom Lane Date: Thu, 1 Nov 2007 19:06:01 +0000 (+0000) Subject: Update discussion of shared memory sizing for 8.3: adjust multipliers, X-Git-Tag: REL8_3_BETA3~150 X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=388c7e28c517d3077bfa9de3058cd98dc938a451;p=postgresql Update discussion of shared memory sizing for 8.3: adjust multipliers, mention autovacuum_max_workers. Minor copy-editing too. --- diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index 9a724098a7..2181ccd3c0 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1,4 +1,4 @@ - + Operating System Environment @@ -478,9 +478,10 @@ psql: could not connect to server: No such file or directory relevant for PostgreSQL). Almost all modern operating systems provide these features, but not all of them have them turned on or sufficiently sized by default, especially systems - with BSD heritage. (For the Windows - port, PostgreSQL provides its own replacement - implementation of these facilities.) + with BSD heritage. (On Windows, + PostgreSQL provides its own replacement + implementation of these facilities, and so most of this section + can be disregarded.) @@ -550,13 +551,13 @@ psql: could not connect to server: No such file or directory SEMMNI Maximum number of semaphore identifiers (i.e., sets) - at least ceil(max_connections / 16) + at least ceil((max_connections + autovacuum_max_workers) / 16) SEMMNS Maximum number of semaphores system-wide - ceil(max_connections / 16) * 17 plus room for other applications + ceil((max_connections + autovacuum_max_workers) / 16) * 17 plus room for other applications @@ -587,18 +588,16 @@ psql: could not connect to server: No such file or directory shared memory parameter is SHMMAX, the maximum size, in bytes, of a shared memory segment. If you get an error message from shmget like Invalid argument, it is - likely that this limit has been exceeded. The size of the required + likely that this limit has been exceeded. The size of the required shared memory segment varies depending on several PostgreSQL configuration parameters, as shown in - . + . (Any error message you might + get will include the exact size of the failed allocation request.) You can, as a temporary solution, lower some of those settings to - avoid the failure. As a rough approximation, you can estimate the - required segment size as 500 kB plus the variable amounts shown in - the table. (Any error message you might get will include the exact - size of the failed allocation request.) While it is possible to get + avoid the failure. While it is possible to get PostgreSQL to run with SHMMAX as small as - 1 MB, you need at least 4 MB for acceptable performance, and desirable - settings are in the tens of megabytes. + 2 MB, you need considerably more for acceptable performance. Desirable + settings are in the tens to hundreds of megabytes. @@ -620,17 +619,21 @@ psql: could not connect to server: No such file or directory PostgreSQL uses one semaphore per allowed connection - (), in sets of 16. Each such set will + () and allowed autovacuum worker + process (), in sets of 16. + Each such set will also contain a 17th semaphore which contains a magic number, to detect collision with semaphore sets used by other applications. The maximum number of semaphores in the system is set by SEMMNS, which consequently must be at least - as high as max_connections plus one extra for each 16 - allowed connections (see the formula in max_connections plus + autovacuum_max_workers, plus one extra for each 16 + allowed connections plus workers (see the formula in ). The parameter SEMMNI determines the limit on the number of semaphore sets that can exist on the system at one time. Hence this parameter must be at - least ceil(max_connections / 16). Lowering the number + least ceil((max_connections + autovacuum_max_workers) / 16). + Lowering the number of allowed connections is a temporary workaround for failures, which are usually confusingly worded No space left on device, from the function semget. @@ -675,7 +678,7 @@ psql: could not connect to server: No such file or directory sort of configuration commonly used for other databases such as DB/2. - It might , however, be necessary to modify the global + It might, however, be necessary to modify the global ulimit information in /etc/security/limits, as the default hard limits for file sizes (fsize) and numbers of @@ -865,8 +868,9 @@ options SEMMAP=256 LinuxIPC configuration - The default settings are only suitable for small installations - (the default maximum segment size is 32 MB). However, the remaining + The default maximum segment size is 32 MB, which is only adequate + for small PostgreSQL installations. + However, the remaining defaults are quite generously sized, and usually do not require changes. The maximum shared memory segment size can be changed via the sysctl interface. For example, to allow 128 MB, @@ -985,7 +989,7 @@ kern.sysv.shmall=1024 At least in version 2.6, the default maximum size of a shared - memory segments is too low for PostgreSQL. The + memory segment is too low for PostgreSQL. The relevant settings can be changed in /etc/system, for example: @@ -1051,24 +1055,29 @@ set semsys:seminfo_semmsl=32 Name - Approximate multiplier (bytes per increment) + Approximate multiplier (bytes per increment) as of 8.3 - 400 + 270 * + 1800 + 270 * + + + + + 1800 + 270 * - 600 + 270 * + 770 + 270 * - 8300 (assuming 8 kB BLCKSZ) + 8400 (assuming 8 kB BLCKSZ) @@ -1085,6 +1094,11 @@ set semsys:seminfo_semmsl=32 6 + + + Fixed space requirements + 770 kB +