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Fix shmem allocation size. #42

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Merged
merged 1 commit into from
Mar 31, 2022
Merged

Fix shmem allocation size. #42

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42 changes: 36 additions & 6 deletions pg_wait_sampling.c
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,10 @@
#include "miscadmin.h"
#include "optimizer/planner.h"
#include "pgstat.h"
#include "postmaster/autovacuum.h"
#if PG_VERSION_NUM >= 120000
#include "replication/walsender.h"
#endif
#include "storage/ipc.h"
#include "storage/pg_shmem.h"
#include "storage/procarray.h"
Expand Down Expand Up @@ -66,20 +70,46 @@ static void pgws_ExecutorEnd(QueryDesc *queryDesc);

/*
* Calculate max processes count.
* Look at InitProcGlobal (proc.c) and TotalProcs variable in it
* if something wrong here.
*
* The value has to be in sync with ProcGlobal->allProcCount, initialized in
* InitProcGlobal() (proc.c).
*
* We calculate the value here as it won't initialized when we need need
* it during _PG_init().
*
* Note that the value returned during _PG_init() might be different from the
* value returned later if some third-party modules change one of the
* underlying GUC. This isn't ideal but can't lead to a crash, as the value
* returned during _PG_init() is only used to ask for additional shmem with
* RequestAddinShmemSpace(), and postgres has an extra 100kB of shmem to
* compensate some small unaccounted usage. So if the value later changes, we
* will allocate and initialize the new (and correct) memory size, which
* will either work thanks for the extra 100kB of shmem, of fail (and prevent
* postgres startup) due to an out of shared memory error.
*/
static int
get_max_procs_count(void)
{
int count = 0;

/* MyProcs, including autovacuum workers and launcher */
count += MaxBackends;
/*
* MaxBackends: bgworkers, autovacuum workers and launcher.
* This has to be in sync with the value computed in
* InitializeMaxBackends() (postinit.c)
*/
count += MaxConnections + autovacuum_max_workers + 1
+ max_worker_processes;

/*
* Starting with pg12, wal senders aren't part of MaxConnections anymore
* and have to be accounted for.
*/
#if PG_VERSION_NUM >= 120000
count += max_wal_senders;
#endif

/* AuxiliaryProcs */
count += NUM_AUXILIARY_PROCS;
/* Prepared xacts */
count += max_prepared_xacts;

return count;
}
Expand Down