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Allow maximum number of backends to be set at configure time

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(--with-maxbackends).  Add a postmaster switch (-N backends) that allows
the limit to be reduced at postmaster start time.  (You can't increase it,
sorry to say, because there are still some fixed-size arrays.)
Grab the number of semaphores indicated by min(MAXBACKENDS, -N) at
postmaster startup, so that this particular form of bogus configuration
is exposed immediately rather than under heavy load.
This commit is contained in:
Tom Lane
1999-02-19 06:06:39 +00:00
parent 612b8434e4
commit e77b630cf0
14 changed files with 502 additions and 392 deletions
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67
src/backend/storage/lmgr/proc.c
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@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.48 1999/02/13 23:18:28 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.49 1999/02/19 06:06:08 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -46,7 +46,7 @@
* This is so that we can support more backends. (system-wide semaphore
* sets run out pretty fast.) -ay 4/95
*
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.48 1999/02/13 23:18:28 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/storage/lmgr/proc.c,v 1.49 1999/02/19 06:06:08 tgl Exp $
*/
#include <sys/time.h>
#include <unistd.h>
@ -108,13 +108,24 @@ static void ProcFreeSem(IpcSemaphoreKey semKey, int semNum);
/*
* InitProcGlobal -
* initializes the global process table. We put it here so that
* the postmaster can do this initialization. (ProcFreeAllSem needs
* the postmaster can do this initialization. (ProcFreeAllSemaphores needs
* to read this table on exiting the postmaster. If we have the first
* backend do this, starting up and killing the postmaster without
* starting any backends will be a problem.)
*
* We also allocate all the per-process semaphores we will need to support
* the requested number of backends. We used to allocate semaphores
* only when backends were actually started up, but that is bad because
* it lets Postgres fail under load --- a lot of Unix systems are
* (mis)configured with small limits on the number of semaphores, and
* running out when trying to start another backend is a common failure.
* So, now we grab enough semaphores to support the desired max number
* of backends immediately at initialization --- if the sysadmin has set
* MaxBackends higher than his kernel will support, he'll find out sooner
* rather than later.
*/
void
InitProcGlobal(IPCKey key)
InitProcGlobal(IPCKey key, int maxBackends)
{
bool found = false;
@ -134,6 +145,24 @@ InitProcGlobal(IPCKey key)
ProcGlobal->currKey = IPCGetProcessSemaphoreInitKey(key);
for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
ProcGlobal->freeSemMap[i] = 0;
/* Pre-create the semaphores for the first maxBackends processes */
for (i = 0;
i < (maxBackends+PROC_NSEMS_PER_SET-1) / PROC_NSEMS_PER_SET;
i++)
{
IPCKey semKey = ProcGlobal->currKey + i;
int semId;
int semstat;
semId = IpcSemaphoreCreate(semKey,
PROC_NSEMS_PER_SET,
IPCProtection,
IpcSemaphoreDefaultStartValue,
0,
&semstat);
/* mark this sema set allocated */
ProcGlobal->freeSemMap[i] = (1 << PROC_NSEMS_PER_SET);
}
}
}
@ -222,6 +251,11 @@ InitProcess(IPCKey key)
ProcGetNewSemKeyAndNum(&semKey, &semNum);
/* Note: because of the pre-allocation done in InitProcGlobal,
* this call should always attach to an existing semaphore.
* It will (try to) create a new group of semaphores only if
* the postmaster tries to start more backends than it said it would.
*/
semId = IpcSemaphoreCreate(semKey,
PROC_NSEMS_PER_SET,
IPCProtection,
@ -823,20 +857,20 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
{
int i;
int32 *freeSemMap = ProcGlobal->freeSemMap;
unsigned int fullmask;
int32 fullmask = (1 << (PROC_NSEMS_PER_SET+1)) - 1;
/*
* we hold ProcStructLock when entering this routine. We scan through
* the bitmap to look for a free semaphore.
*/
fullmask = ~0 >> (32 - PROC_NSEMS_PER_SET);
for (i = 0; i < MAX_PROC_SEMS / PROC_NSEMS_PER_SET; i++)
{
int mask = 1;
int j;
if (freeSemMap[i] == fullmask)
continue; /* none free for this set */
continue; /* this set is fully allocated */
for (j = 0; j < PROC_NSEMS_PER_SET; j++)
{
@ -845,8 +879,9 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
/*
* a free semaphore found. Mark it as allocated.
* Also set the bit indicating whole set is allocated.
*/
freeSemMap[i] |= mask;
freeSemMap[i] |= mask + (1 << PROC_NSEMS_PER_SET);
*key = ProcGlobal->currKey + i;
*semNum = j;
@ -862,8 +897,7 @@ ProcGetNewSemKeyAndNum(IPCKey *key, int *semNum)
/*
* ProcFreeSem -
* free up our semaphore in the semaphore set. If we're the last one
* in the set, also remove the semaphore set.
* free up our semaphore in the semaphore set.
*/
static void
ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
@ -876,14 +910,19 @@ ProcFreeSem(IpcSemaphoreKey semKey, int semNum)
mask = ~(1 << semNum);
freeSemMap[i] &= mask;
if (freeSemMap[i] == 0)
IpcSemaphoreKill(semKey);
/* Formerly we'd release a semaphore set if it was now completely unused,
* but now we keep the semaphores to ensure we won't run out when
* starting new backends --- cf. InitProcGlobal. Note that the
* PROC_NSEMS_PER_SET+1'st bit of the freeSemMap entry remains set to
* indicate it is still allocated; ProcFreeAllSemaphores() needs that.
*/
}
/*
* ProcFreeAllSemaphores -
* on exiting the postmaster, we free up all the semaphores allocated
* to the lmgrs of the backends.
* called at shmem_exit time, ie when exiting the postmaster or
* destroying shared state for a failed set of backends.
* Free up all the semaphores allocated to the lmgrs of the backends.
*/
void
ProcFreeAllSemaphores()