From f4763273a7f4649d4c50699b590c0b4b8077cb95 Mon Sep 17 00:00:00 2001 From: Michael Paquier Date: Thu, 9 Sep 2021 13:10:38 +0900 Subject: [PATCH v9 2/2] Provide useful values for 'postgres -C' with runtime-computed GUCs. The -C option is handled before a small subset of GUCs that are computed at runtime are initialized. Unfortunately, we cannot move this handling to after they are initialized without disallowing 'postgres -C' on a running server. One notable reason for this is that loadable libraries' _PG_init() functions are called before all runtime-computed GUCs are initialized, and this is not guaranteed to be safe to do on running servers. In order to provide useful values for 'postgres -C' for runtime- computed GUCs, this change adds a new section for handling just these GUCs just before shared memory is initialized. While users won't be able to use -C for runtime-computed GUCs on running servers, providing a useful value with this restriction seems better than not providing a useful value at all. --- src/include/utils/guc.h | 6 ++++ src/backend/postmaster/postmaster.c | 50 +++++++++++++++++++++++++---- src/backend/utils/misc/guc.c | 10 +++--- doc/src/sgml/ref/postgres-ref.sgml | 12 +++++-- doc/src/sgml/runtime.sgml | 33 +++++++------------ 5 files changed, 75 insertions(+), 36 deletions(-) diff --git a/src/include/utils/guc.h b/src/include/utils/guc.h index a7c3a4958e..aa18d304ac 100644 --- a/src/include/utils/guc.h +++ b/src/include/utils/guc.h @@ -229,6 +229,12 @@ typedef enum #define GUC_EXPLAIN 0x100000 /* include in explain */ +/* + * GUC_RUNTIME_COMPUTED is intended for runtime-computed GUCs that are only + * available via 'postgres -C' if the server is not running. + */ +#define GUC_RUNTIME_COMPUTED 0x200000 + #define GUC_UNIT (GUC_UNIT_MEMORY | GUC_UNIT_TIME) diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index b2fe420c3c..f601b9e5d1 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -896,15 +896,31 @@ PostmasterMain(int argc, char *argv[]) if (output_config_variable != NULL) { /* - * "-C guc" was specified, so print GUC's value and exit. No extra - * permission check is needed because the user is reading inside the - * data dir. + * If this is a runtime-computed GUC, it hasn't yet been initialized, + * and the present value is not useful. However, this is a convenient + * place to print the value for most GUCs because it is safe to run + * postmaster startup to this point even if the server is already + * running. For the handful of runtime-computed GUCs that we can't + * provide meaningful values for yet, we wait until later in postmaster + * startup to print the value. We won't be able to use -C on running + * servers for those GUCs, but otherwise this option is unusable for + * them. */ - const char *config_val = GetConfigOption(output_config_variable, - false, false); + int flags = GetConfigOptionFlags(output_config_variable, true); - puts(config_val ? config_val : ""); - ExitPostmaster(0); + if ((flags & GUC_RUNTIME_COMPUTED) == 0) + { + /* + * "-C guc" was specified, so print GUC's value and exit. No extra + * permission check is needed because the user is reading inside + * the data dir. + */ + const char *config_val = GetConfigOption(output_config_variable, + false, false); + + puts(config_val ? config_val : ""); + ExitPostmaster(0); + } } /* Verify that DataDir looks reasonable */ @@ -1033,6 +1049,26 @@ PostmasterMain(int argc, char *argv[]) */ InitializeShmemGUCs(); + /* + * If -C was specified with a runtime-computed GUC, we held off printing + * the value earlier, as the GUC was not yet initialized. We handle -C for + * most GUCs before we lock the data directory so that the option may be + * used on a running server. However, a handful of GUCs are runtime- + * computed and do not have meaningful values until after locking the data + * directory, and we cannot safely calculate their values earlier on a + * running server. At this point, such GUCs should be properly + * initialized, and we haven't yet set up shared memory, so this is a good + * time to handle the -C option for these special GUCs. + */ + if (output_config_variable != NULL) + { + const char *config_val = GetConfigOption(output_config_variable, + false, false); + + puts(config_val ? config_val : ""); + ExitPostmaster(0); + } + /* * Set up shared memory and semaphores. */ diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 8edfd07340..50e60b270b 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -1984,7 +1984,7 @@ static struct config_bool ConfigureNamesBool[] = {"data_checksums", PGC_INTERNAL, PRESET_OPTIONS, gettext_noop("Shows whether data checksums are turned on for this cluster."), NULL, - GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE + GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED }, &data_checksums, false, @@ -2229,7 +2229,7 @@ static struct config_int ConfigureNamesInt[] = {"huge_pages_required", PGC_INTERNAL, PRESET_OPTIONS, gettext_noop("Shows the number of huge pages needed for the main shared memory area."), gettext_noop("-1 indicates that the value could not be determined."), - GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE + GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED }, &huge_pages_required, -1, -1, INT_MAX, @@ -2354,7 +2354,7 @@ static struct config_int ConfigureNamesInt[] = {"shared_memory_size", PGC_INTERNAL, PRESET_OPTIONS, gettext_noop("Shows the size of the server's main shared memory area (rounded up to the nearest MB)."), NULL, - GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_UNIT_MB + GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_UNIT_MB | GUC_RUNTIME_COMPUTED }, &shared_memory_size_mb, 0, 0, INT_MAX, @@ -2419,7 +2419,7 @@ static struct config_int ConfigureNamesInt[] = "in the form accepted by the chmod and umask system " "calls. (To use the customary octal format the number " "must start with a 0 (zero).)"), - GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE + GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED }, &data_directory_mode, 0700, 0000, 0777, @@ -3243,7 +3243,7 @@ static struct config_int ConfigureNamesInt[] = {"wal_segment_size", PGC_INTERNAL, PRESET_OPTIONS, gettext_noop("Shows the size of write ahead log segments."), NULL, - GUC_UNIT_BYTE | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE + GUC_UNIT_BYTE | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_RUNTIME_COMPUTED }, &wal_segment_size, DEFAULT_XLOG_SEG_SIZE, diff --git a/doc/src/sgml/ref/postgres-ref.sgml b/doc/src/sgml/ref/postgres-ref.sgml index 4aaa7abe1a..89cc3cdb4e 100644 --- a/doc/src/sgml/ref/postgres-ref.sgml +++ b/doc/src/sgml/ref/postgres-ref.sgml @@ -133,13 +133,21 @@ PostgreSQL documentation Prints the value of the named run-time parameter, and exits. - (See the option above for details.) This can - be used on a running server, and returns values from + (See the option above for details.) This + returns values from postgresql.conf, modified by any parameters supplied in this invocation. It does not reflect parameters supplied when the cluster was started. + + This can be used on a running server for most parameters. However, + the server must be shut down for some runtime-computed parameters + (e.g., , + , and + ). + + This option is meant for other programs that interact with a server instance, such as , to query configuration diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml index f1cbc1d9e9..d955639900 100644 --- a/doc/src/sgml/runtime.sgml +++ b/doc/src/sgml/runtime.sgml @@ -1442,32 +1442,21 @@ export PG_OOM_ADJUST_VALUE=0 with CONFIG_HUGETLBFS=y and CONFIG_HUGETLB_PAGE=y. You will also have to configure the operating system to provide enough huge pages of the desired size. - To estimate the number of huge pages needed, start - PostgreSQL without huge pages enabled and check - the postmaster's anonymous shared memory segment size, as well as the - system's default and supported huge page sizes, using the - /proc and /sys file systems. - This might look like: + To estimate the number of huge pages needed, use the + postgres command to see the value of + . This might look like: -$ head -1 $PGDATA/postmaster.pid -4170 -$ pmap 4170 | awk '/rw-s/ && /zero/ {print $2}' -6490428K -$ grep ^Hugepagesize /proc/meminfo -Hugepagesize: 2048 kB -$ ls /sys/kernel/mm/hugepages -hugepages-1048576kB hugepages-2048kB +$ postgres -D $PGDATA -C huge_pages_required +3170 - In this example the default is 2MB, but you can also explicitly request - either 2MB or 1GB with . + Note that you can explicitly request either 2MB or 1GB huge pages with + . - Assuming 2MB huge pages, - 6490428 / 2048 gives approximately - 3169.154, so in this example we need at - least 3170 huge pages. A larger setting would be - appropriate if other programs on the machine also need huge pages. - We can set this with: + While we need at least 3170 huge pages in this + example, a larger setting would be appropriate if other programs on + the machine also need huge pages. We can allocate the huge pages + with: # sysctl -w vm.nr_hugepages=3170 -- 2.33.0