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Redefine max_files_per_process to control additionally opened files

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Until now max_files_per_process=N limited each backend to open N files in
total (minus a safety factor), even if there were already more files opened in
postmaster and inherited by backends.  Change max_files_per_process to control
how many additional files each process is allowed to open.

The main motivation for this is the patch to add io_method=io_uring, which
needs to open one file for each backend.  Without this patch, even if
RLIMIT_NOFILE is high enough, postmaster will fail in set_max_safe_fds() if
started with a high max_connections.  The cause of the failure is that, until
now, set_max_safe_fds() subtracted the already open files from
max_files_per_process.

Reviewed-by: Noah Misch <noah@leadboat.com>
Discussion: https://postgr.es/m/w6uiicyou7hzq47mbyejubtcyb2rngkkf45fk4q7inue5kfbeo@bbfad3qyubvs
Discussion: https://postgr.es/m/CAGECzQQh6VSy3KG4pN1d=h9J=D1rStFCMR+t7yh_Kwj-g87aLQ@mail.gmail.com
This commit is contained in:
Andres Freund
2025-03-24 18:20:18 -04:00
parent 7d559c8580
commit adb5f85fa5
3 changed files with 15 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

14
src/backend/storage/file/fd.c
View File

@ -1047,16 +1047,17 @@ set_max_safe_fds(void)
/*----------
* We want to set max_safe_fds to
* MIN(usable_fds, max_files_per_process - already_open)
* MIN(usable_fds, max_files_per_process)
* less the slop factor for files that are opened without consulting
* fd.c. This ensures that we won't exceed either max_files_per_process
* or the experimentally-determined EMFILE limit.
* fd.c. This ensures that we won't allow to open more than
* max_files_per_process, or the experimentally-determined EMFILE limit,
* additional files.
*----------
*/
count_usable_fds(max_files_per_process,
&usable_fds, &already_open);
max_safe_fds = Min(usable_fds, max_files_per_process - already_open);
max_safe_fds = Min(usable_fds, max_files_per_process);
/*
* Take off the FDs reserved for system() etc.
@ -1070,9 +1071,10 @@ set_max_safe_fds(void)
ereport(FATAL,
(errcode(ERRCODE_INSUFFICIENT_RESOURCES),
errmsg("insufficient file descriptors available to start server process"),
errdetail("System allows %d, server needs at least %d.",
errdetail("System allows %d, server needs at least %d, %d files are already open.",
max_safe_fds + NUM_RESERVED_FDS,
FD_MINFREE + NUM_RESERVED_FDS)));
FD_MINFREE + NUM_RESERVED_FDS,
already_open)));
elog(DEBUG2, "max_safe_fds = %d, usable_fds = %d, already_open = %d",
max_safe_fds, usable_fds, already_open);

2
src/backend/utils/misc/guc_tables.c
View File

@ -2680,7 +2680,7 @@ struct config_int ConfigureNamesInt[] =
{
{"max_files_per_process", PGC_POSTMASTER, RESOURCES_KERNEL,
gettext_noop("Sets the maximum number of simultaneously open files for each server process."),
gettext_noop("Sets the maximum number of files each server process is allowed to open simultaneously."),
NULL
},
&max_files_per_process,