From 09c5f97fac0b14d82d2108d4b31777c7a639608e Mon Sep 17 00:00:00 2001 From: Alexander Korotkov Date: Sun, 16 Nov 2025 14:06:50 +0200 Subject: [PATCH v3] Optimize shared memory usage for WaitLSNProcInfo We need separate pairing heaps for different WaitLSNType's, because there might be waiters for different LSN's at the same time. However, one process can wait only for one type of LSN at a time. So, no need for inHeap and heapNode fields to be arrays. Discussion: https://postgr.es/m/CAPpHfdsBR-7sDtXFJ1qpJtKiohfGoj%3DvqzKVjWxtWsWidx7G_A%40mail.gmail.com Author: Alexander Korotkov Reviewed-by: Xuneng Zhou --- src/backend/access/transam/xlogwait.c | 42 ++++++++++++--------------- src/include/access/xlogwait.h | 14 ++++++--- 2 files changed, 29 insertions(+), 27 deletions(-) diff --git a/src/backend/access/transam/xlogwait.c b/src/backend/access/transam/xlogwait.c index 78de93db47f..98aa5f1e4a2 100644 --- a/src/backend/access/transam/xlogwait.c +++ b/src/backend/access/transam/xlogwait.c @@ -90,7 +90,7 @@ WaitLSNShmemInit(void) for (i = 0; i < WAIT_LSN_TYPE_COUNT; i++) { pg_atomic_init_u64(&waitLSNState->minWaitedLSN[i], PG_UINT64_MAX); - pairingheap_initialize(&waitLSNState->waitersHeap[i], waitlsn_cmp, (void *) (uintptr_t) i); + pairingheap_initialize(&waitLSNState->waitersHeap[i], waitlsn_cmp, NULL); } /* Initialize process info array */ @@ -106,9 +106,8 @@ WaitLSNShmemInit(void) static int waitlsn_cmp(const pairingheap_node *a, const pairingheap_node *b, void *arg) { - int i = (uintptr_t) arg; - const WaitLSNProcInfo *aproc = pairingheap_const_container(WaitLSNProcInfo, heapNode[i], a); - const WaitLSNProcInfo *bproc = pairingheap_const_container(WaitLSNProcInfo, heapNode[i], b); + const WaitLSNProcInfo *aproc = pairingheap_const_container(WaitLSNProcInfo, heapNode, a); + const WaitLSNProcInfo *bproc = pairingheap_const_container(WaitLSNProcInfo, heapNode, b); if (aproc->waitLSN < bproc->waitLSN) return 1; @@ -132,7 +131,7 @@ updateMinWaitedLSN(WaitLSNType lsnType) if (!pairingheap_is_empty(&waitLSNState->waitersHeap[i])) { pairingheap_node *node = pairingheap_first(&waitLSNState->waitersHeap[i]); - WaitLSNProcInfo *procInfo = pairingheap_container(WaitLSNProcInfo, heapNode[i], node); + WaitLSNProcInfo *procInfo = pairingheap_container(WaitLSNProcInfo, heapNode, node); minWaitedLSN = procInfo->waitLSN; } @@ -154,10 +153,11 @@ addLSNWaiter(XLogRecPtr lsn, WaitLSNType lsnType) procInfo->procno = MyProcNumber; procInfo->waitLSN = lsn; + procInfo->lsnType = lsnType; - Assert(!procInfo->inHeap[i]); - pairingheap_add(&waitLSNState->waitersHeap[i], &procInfo->heapNode[i]); - procInfo->inHeap[i] = true; + Assert(!procInfo->inHeap); + pairingheap_add(&waitLSNState->waitersHeap[i], &procInfo->heapNode); + procInfo->inHeap = true; updateMinWaitedLSN(lsnType); LWLockRelease(WaitLSNLock); @@ -176,10 +176,12 @@ deleteLSNWaiter(WaitLSNType lsnType) LWLockAcquire(WaitLSNLock, LW_EXCLUSIVE); - if (procInfo->inHeap[i]) + Assert(procInfo->lsnType == lsnType); + + if (procInfo->inHeap) { - pairingheap_remove(&waitLSNState->waitersHeap[i], &procInfo->heapNode[i]); - procInfo->inHeap[i] = false; + pairingheap_remove(&waitLSNState->waitersHeap[i], &procInfo->heapNode); + procInfo->inHeap = false; updateMinWaitedLSN(lsnType); } @@ -228,7 +230,7 @@ wakeupWaiters(WaitLSNType lsnType, XLogRecPtr currentLSN) WaitLSNProcInfo *procInfo; /* Get procInfo using appropriate heap node */ - procInfo = pairingheap_container(WaitLSNProcInfo, heapNode[i], node); + procInfo = pairingheap_container(WaitLSNProcInfo, heapNode, node); if (XLogRecPtrIsValid(currentLSN) && procInfo->waitLSN > currentLSN) break; @@ -238,7 +240,7 @@ wakeupWaiters(WaitLSNType lsnType, XLogRecPtr currentLSN) (void) pairingheap_remove_first(&waitLSNState->waitersHeap[i]); /* Update appropriate flag */ - procInfo->inHeap[i] = false; + procInfo->inHeap = false; if (numWakeUpProcs == WAKEUP_PROC_STATIC_ARRAY_SIZE) break; @@ -289,20 +291,14 @@ WaitLSNCleanup(void) { if (waitLSNState) { - int i; - /* - * We do a fast-path check of the heap flags without the lock. These - * flags are set to true only by the process itself. So, it's only + * We do a fast-path check of the inHeap flag without the lock. This + * flag is set to true only by the process itself. So, it's only * possible to get a false positive. But that will be eliminated by a * recheck inside deleteLSNWaiter(). */ - - for (i = 0; i < (int) WAIT_LSN_TYPE_COUNT; i++) - { - if (waitLSNState->procInfos[MyProcNumber].inHeap[i]) - deleteLSNWaiter((WaitLSNType) i); - } + if (waitLSNState->procInfos[MyProcNumber].inHeap) + deleteLSNWaiter(waitLSNState->procInfos[MyProcNumber].lsnType); } } diff --git a/src/include/access/xlogwait.h b/src/include/access/xlogwait.h index f43e481c3b9..e607441d618 100644 --- a/src/include/access/xlogwait.h +++ b/src/include/access/xlogwait.h @@ -50,14 +50,20 @@ typedef struct WaitLSNProcInfo /* LSN, which this process is waiting for */ XLogRecPtr waitLSN; + /* The type of LSN to wait */ + WaitLSNType lsnType; + /* Process to wake up once the waitLSN is reached */ ProcNumber procno; - /* Heap membership flags for LSN types */ - bool inHeap[WAIT_LSN_TYPE_COUNT]; + /* + * Heap membership flag. A process can wait for only one LSN type at a + * time, so a single flag suffices (tracked by the lsnType field). + */ + bool inHeap; - /* Heap nodes for LSN types */ - pairingheap_node heapNode[WAIT_LSN_TYPE_COUNT]; + /* Pairing heap node for the waiters' heap (one per process) */ + pairingheap_node heapNode; } WaitLSNProcInfo; /* -- 2.39.5 (Apple Git-154)