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michaelpqmichaelpq
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Move the shared memory size calculation to its own function
This change refactors the shared memory size calculation in CreateSharedMemoryAndSemaphores() to its own function. This is intended for use in a future change related to the setup of huge pages and shared memory with some GUCs, while useful on its own for extensions. Author: Nathan Bossart Discussion: https://postgr.es/m/F2772387-CE0F-46BF-B5F1-CC55516EB885@amazon.com
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-59
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2 files changed

+84
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‎src/backend/storage/ipc/ipci.c‎

Lines changed: 83 additions & 59 deletions
Original file line numberDiff line numberDiff line change
@@ -75,6 +75,87 @@ RequestAddinShmemSpace(Size size)
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total_addin_request = add_size(total_addin_request, size);
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}
7777

78+
/*
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* CalculateShmemSize
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* Calculates the amount of shared memory and number of semaphores needed.
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*
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* If num_semaphores is not NULL, it will be set to the number of semaphores
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* required.
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*
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* Note that this function freezes the additional shared memory request size
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* from loadable modules.
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*/
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Size
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CalculateShmemSize(int *num_semaphores)
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{
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Size size;
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int numSemas;
93+
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/* Compute number of semaphores we'll need */
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numSemas = ProcGlobalSemas();
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numSemas += SpinlockSemas();
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/* Return the number of semaphores if requested by the caller */
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if (num_semaphores)
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*num_semaphores = numSemas;
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/*
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* Size of the Postgres shared-memory block is estimated via moderately-
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* accurate estimates for the big hogs, plus 100K for the stuff that's too
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* small to bother with estimating.
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*
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* We take some care to ensure that the total size request doesn't
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* overflow size_t. If this gets through, we don't need to be so careful
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* during the actual allocation phase.
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*/
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size = 100000;
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size = add_size(size, PGSemaphoreShmemSize(numSemas));
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size = add_size(size, SpinlockSemaSize());
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size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
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sizeof(ShmemIndexEnt)));
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size = add_size(size, dsm_estimate_size());
117+
size = add_size(size, BufferShmemSize());
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size = add_size(size, LockShmemSize());
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size = add_size(size, PredicateLockShmemSize());
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size = add_size(size, ProcGlobalShmemSize());
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size = add_size(size, XLOGShmemSize());
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size = add_size(size, CLOGShmemSize());
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size = add_size(size, CommitTsShmemSize());
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size = add_size(size, SUBTRANSShmemSize());
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size = add_size(size, TwoPhaseShmemSize());
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size = add_size(size, BackgroundWorkerShmemSize());
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size = add_size(size, MultiXactShmemSize());
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size = add_size(size, LWLockShmemSize());
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size = add_size(size, ProcArrayShmemSize());
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size = add_size(size, BackendStatusShmemSize());
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size = add_size(size, SInvalShmemSize());
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size = add_size(size, PMSignalShmemSize());
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size = add_size(size, ProcSignalShmemSize());
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size = add_size(size, CheckpointerShmemSize());
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size = add_size(size, AutoVacuumShmemSize());
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size = add_size(size, ReplicationSlotsShmemSize());
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size = add_size(size, ReplicationOriginShmemSize());
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size = add_size(size, WalSndShmemSize());
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size = add_size(size, WalRcvShmemSize());
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size = add_size(size, PgArchShmemSize());
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size = add_size(size, ApplyLauncherShmemSize());
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size = add_size(size, SnapMgrShmemSize());
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size = add_size(size, BTreeShmemSize());
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size = add_size(size, SyncScanShmemSize());
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size = add_size(size, AsyncShmemSize());
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#ifdef EXEC_BACKEND
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size = add_size(size, ShmemBackendArraySize());
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#endif
149+
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/* freeze the addin request size and include it */
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addin_request_allowed = false;
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size = add_size(size, total_addin_request);
153+
154+
/* might as well round it off to a multiple of a typical page size */
155+
size = add_size(size, 8192 - (size % 8192));
156+
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return size;
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}
78159

79160
/*
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* CreateSharedMemoryAndSemaphores
@@ -102,65 +183,8 @@ CreateSharedMemoryAndSemaphores(void)
102183
Size size;
103184
int numSemas;
104185

105-
/* Compute number of semaphores we'll need */
106-
numSemas = ProcGlobalSemas();
107-
numSemas += SpinlockSemas();
108-
109-
/*
110-
* Size of the Postgres shared-memory block is estimated via
111-
* moderately-accurate estimates for the big hogs, plus 100K for the
112-
* stuff that's too small to bother with estimating.
113-
*
114-
* We take some care during this phase to ensure that the total size
115-
* request doesn't overflow size_t. If this gets through, we don't
116-
* need to be so careful during the actual allocation phase.
117-
*/
118-
size = 100000;
119-
size = add_size(size, PGSemaphoreShmemSize(numSemas));
120-
size = add_size(size, SpinlockSemaSize());
121-
size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
122-
sizeof(ShmemIndexEnt)));
123-
size = add_size(size, dsm_estimate_size());
124-
size = add_size(size, BufferShmemSize());
125-
size = add_size(size, LockShmemSize());
126-
size = add_size(size, PredicateLockShmemSize());
127-
size = add_size(size, ProcGlobalShmemSize());
128-
size = add_size(size, XLOGShmemSize());
129-
size = add_size(size, CLOGShmemSize());
130-
size = add_size(size, CommitTsShmemSize());
131-
size = add_size(size, SUBTRANSShmemSize());
132-
size = add_size(size, TwoPhaseShmemSize());
133-
size = add_size(size, BackgroundWorkerShmemSize());
134-
size = add_size(size, MultiXactShmemSize());
135-
size = add_size(size, LWLockShmemSize());
136-
size = add_size(size, ProcArrayShmemSize());
137-
size = add_size(size, BackendStatusShmemSize());
138-
size = add_size(size, SInvalShmemSize());
139-
size = add_size(size, PMSignalShmemSize());
140-
size = add_size(size, ProcSignalShmemSize());
141-
size = add_size(size, CheckpointerShmemSize());
142-
size = add_size(size, AutoVacuumShmemSize());
143-
size = add_size(size, ReplicationSlotsShmemSize());
144-
size = add_size(size, ReplicationOriginShmemSize());
145-
size = add_size(size, WalSndShmemSize());
146-
size = add_size(size, WalRcvShmemSize());
147-
size = add_size(size, PgArchShmemSize());
148-
size = add_size(size, ApplyLauncherShmemSize());
149-
size = add_size(size, SnapMgrShmemSize());
150-
size = add_size(size, BTreeShmemSize());
151-
size = add_size(size, SyncScanShmemSize());
152-
size = add_size(size, AsyncShmemSize());
153-
#ifdef EXEC_BACKEND
154-
size = add_size(size, ShmemBackendArraySize());
155-
#endif
156-
157-
/* freeze the addin request size and include it */
158-
addin_request_allowed = false;
159-
size = add_size(size, total_addin_request);
160-
161-
/* might as well round it off to a multiple of a typical page size */
162-
size = add_size(size, 8192 - (size % 8192));
163-
186+
/* Compute the size of the shared-memory block */
187+
size = CalculateShmemSize(&numSemas);
164188
elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
165189

166190
/*

‎src/include/storage/ipc.h‎

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -77,6 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
7777
/* ipci.c */
7878
extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
7979

80+
extern Size CalculateShmemSize(int *num_semaphores);
8081
extern void CreateSharedMemoryAndSemaphores(void);
8182

8283
#endif /* IPC_H */

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