From 2fd801aad661d8c8de816f10c014edd7705dd3f0 Mon Sep 17 00:00:00 2001 From: Andres Freund Date: Sun, 26 Jan 2025 14:10:58 -0500 Subject: [PATCH v2 1/4] Move MAX_BACKENDS to procnumber.h MAX_BACKENDS influences many things besides postmaster. I e.g. noticed that we don't have static assertions ensuring BUF_REFCOUNT_MASK is big enough for MAX_BACKENDS, adding them would require including postmaster.h in buf_internals.h which doesn't seem right. While at that, add MAX_BACKENDS_BITS, as that's useful in various places for static assertions (to be added in subsequent commits). Discussion: https://postgr.es/m/wptizm4qt6yikgm2pt52xzyv6ycmqiutloyvypvmagn7xvqkce@d4xuv3mylpg4 --- src/include/postmaster/postmaster.h | 12 ------------ src/include/storage/procnumber.h | 13 +++++++++++++ src/backend/storage/lmgr/lwlock.c | 2 +- src/backend/utils/adt/xid8funcs.c | 2 +- src/backend/utils/init/postinit.c | 1 + src/backend/utils/misc/guc_tables.c | 1 + 6 files changed, 17 insertions(+), 14 deletions(-) diff --git a/src/include/postmaster/postmaster.h b/src/include/postmaster/postmaster.h index d8a9f14b3b8..b6a3f275a1b 100644 --- a/src/include/postmaster/postmaster.h +++ b/src/include/postmaster/postmaster.h @@ -126,18 +126,6 @@ extern PMChild *AllocDeadEndChild(void); extern bool ReleasePostmasterChildSlot(PMChild *pmchild); extern PMChild *FindPostmasterChildByPid(int pid); -/* - * Note: MAX_BACKENDS is limited to 2^18-1 because that's the width reserved - * for buffer references in buf_internals.h. This limitation could be lifted - * by using a 64bit state; but it's unlikely to be worthwhile as 2^18-1 - * backends exceed currently realistic configurations. Even if that limitation - * were removed, we still could not a) exceed 2^23-1 because inval.c stores - * the ProcNumber as a 3-byte signed integer, b) INT_MAX/4 because some places - * compute 4*MaxBackends without any overflow check. This is rechecked in the - * relevant GUC check hooks and in RegisterBackgroundWorker(). - */ -#define MAX_BACKENDS 0x3FFFF - /* * These values correspond to the special must-be-first options for dispatching * to various subprograms. parse_dispatch_option() can be used to convert an diff --git a/src/include/storage/procnumber.h b/src/include/storage/procnumber.h index 7cf981ab673..fdbecc55dbe 100644 --- a/src/include/storage/procnumber.h +++ b/src/include/storage/procnumber.h @@ -25,6 +25,19 @@ typedef int ProcNumber; #define INVALID_PROC_NUMBER (-1) +/* + * Note: MAX_BACKENDS_BITS is 18 as that is the space available for buffer + * refcounts in buf_internals.h. This limitation could be lifted by using a + * 64bit state; but it's unlikely to be worthwhile as 2^18-1 backends exceed + * currently realistic configurations. Even if that limitation were removed, + * we still could not a) exceed 2^23-1 because inval.c stores the ProcNumber + * as a 3-byte signed integer, b) INT_MAX/4 because some places compute + * 4*MaxBackends without any overflow check. This is rechecked in the + * relevant GUC check hooks and in RegisterBackgroundWorker(). + */ +#define MAX_BACKENDS_BITS 18 +#define MAX_BACKENDS ((1 << MAX_BACKENDS_BITS)-1) + /* * Proc number of this backend (same as GetNumberFromPGProc(MyProc)) */ diff --git a/src/backend/storage/lmgr/lwlock.c b/src/backend/storage/lmgr/lwlock.c index f1e74f184f1..d08144e9c22 100644 --- a/src/backend/storage/lmgr/lwlock.c +++ b/src/backend/storage/lmgr/lwlock.c @@ -80,9 +80,9 @@ #include "pg_trace.h" #include "pgstat.h" #include "port/pg_bitutils.h" -#include "postmaster/postmaster.h" #include "storage/proc.h" #include "storage/proclist.h" +#include "storage/procnumber.h" #include "storage/spin.h" #include "utils/memutils.h" diff --git a/src/backend/utils/adt/xid8funcs.c b/src/backend/utils/adt/xid8funcs.c index 20b28b2528c..88d798fbf4b 100644 --- a/src/backend/utils/adt/xid8funcs.c +++ b/src/backend/utils/adt/xid8funcs.c @@ -32,9 +32,9 @@ #include "lib/qunique.h" #include "libpq/pqformat.h" #include "miscadmin.h" -#include "postmaster/postmaster.h" #include "storage/lwlock.h" #include "storage/procarray.h" +#include "storage/procnumber.h" #include "utils/builtins.h" #include "utils/memutils.h" #include "utils/snapmgr.h" diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c index 01bb6a410cb..318600d6d02 100644 --- a/src/backend/utils/init/postinit.c +++ b/src/backend/utils/init/postinit.c @@ -49,6 +49,7 @@ #include "storage/lmgr.h" #include "storage/proc.h" #include "storage/procarray.h" +#include "storage/procnumber.h" #include "storage/procsignal.h" #include "storage/sinvaladt.h" #include "storage/smgr.h" diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index 03a6dd49154..ad25cbb39c5 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -77,6 +77,7 @@ #include "storage/large_object.h" #include "storage/pg_shmem.h" #include "storage/predicate.h" +#include "storage/procnumber.h" #include "storage/standby.h" #include "tcop/backend_startup.h" #include "tcop/tcopprot.h" -- 2.48.1.76.g4e746b1a31.dirty