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Implement a new facility that allows processes to wait for WAL to reach specific LSNs, both on primary (waiting for flush) and standby (waiting for replay) servers. The implementation uses shared memory with per-backend information organized into pairing heaps, allowing O(1) access to the minimum waited LSN. This enables fast-path checks: after replaying or flushing WAL, the startup process or WAL writer can quickly determine if any waiters need to be awakened. Key components: - New xlogwait.c/h module with WaitForLSNReplay() and WaitForLSNFlush() - Separate pairing heaps for replay and flush waiters - WaitLSN lightweight lock for coordinating shared state - Wait events WAIT_FOR_WAL_REPLAY and WAIT_FOR_WAL_FLUSH for monitoring This infrastructure can be used by features that need to wait for WAL operations to complete. Discussion: https://www.postgresql.org/message-id/flat/CAPpHfdsjtZLVzxjGT8rJHCYbM0D5dwkO+BBjcirozJ6nYbOW8Q@mail.gmail.com Discussion: https://www.postgresql.org/message-id/flat/CABPTF7UNft368x-RgOXkfj475OwEbp%2BVVO-wEXz7StgjD_%3D6sw%40mail.gmail.com Author: Kartyshov Ivan <i.kartyshov@postgrespro.ru> Author: Alexander Korotkov <aekorotkov@gmail.com> Author: Xuneng Zhou <xunengzhou@gmail.com> Reviewed-by: Michael Paquier <michael@paquier.xyz> Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Amit Kapila <amit.kapila16@gmail.com> Reviewed-by: Alexander Lakhin <exclusion@gmail.com> Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com> Reviewed-by: Euler Taveira <euler@eulerto.com> Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi> Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com> Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
99 lines
2.6 KiB
C
99 lines
2.6 KiB
C
/*-------------------------------------------------------------------------
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*
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* xlogwait.h
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* Declarations for LSN replay waiting routines.
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*
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* Copyright (c) 2025, PostgreSQL Global Development Group
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*
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* src/include/access/xlogwait.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef XLOG_WAIT_H
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#define XLOG_WAIT_H
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#include "access/xlogdefs.h"
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#include "lib/pairingheap.h"
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#include "port/atomics.h"
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#include "storage/procnumber.h"
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#include "storage/spin.h"
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#include "tcop/dest.h"
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/*
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* Result statuses for WaitForLSNReplay().
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*/
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typedef enum
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{
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WAIT_LSN_RESULT_SUCCESS, /* Target LSN is reached */
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WAIT_LSN_RESULT_NOT_IN_RECOVERY, /* Recovery ended before or during our
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* wait */
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WAIT_LSN_RESULT_TIMEOUT /* Timeout occurred */
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} WaitLSNResult;
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/*
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* LSN type for waiting facility.
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*/
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typedef enum WaitLSNType
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{
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WAIT_LSN_TYPE_REPLAY = 0, /* Waiting for replay on standby */
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WAIT_LSN_TYPE_FLUSH = 1, /* Waiting for flush on primary */
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WAIT_LSN_TYPE_COUNT = 2
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} WaitLSNType;
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/*
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* WaitLSNProcInfo - the shared memory structure representing information
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* about the single process, which may wait for LSN operations. An item of
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* waitLSNState->procInfos array.
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*/
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typedef struct WaitLSNProcInfo
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{
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/* LSN, which this process is waiting for */
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XLogRecPtr waitLSN;
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/* Process to wake up once the waitLSN is reached */
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ProcNumber procno;
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/* Heap membership flags for LSN types */
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bool inHeap[WAIT_LSN_TYPE_COUNT];
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/* Heap nodes for LSN types */
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pairingheap_node heapNode[WAIT_LSN_TYPE_COUNT];
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} WaitLSNProcInfo;
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/*
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* WaitLSNState - the shared memory state for the LSN waiting facility.
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*/
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typedef struct WaitLSNState
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{
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/*
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* The minimum LSN values some process is waiting for. Used for the
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* fast-path checking if we need to wake up any waiters after replaying a
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* WAL record. Could be read lock-less. Update protected by WaitLSNLock.
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*/
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pg_atomic_uint64 minWaitedLSN[WAIT_LSN_TYPE_COUNT];
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/*
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* A pairing heaps of waiting processes ordered by LSN values (least LSN
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* is on top). Protected by WaitLSNLock.
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*/
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pairingheap waitersHeap[WAIT_LSN_TYPE_COUNT];
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/*
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* An array with per-process information, indexed by the process number.
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* Protected by WaitLSNLock.
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*/
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WaitLSNProcInfo procInfos[FLEXIBLE_ARRAY_MEMBER];
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} WaitLSNState;
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extern PGDLLIMPORT WaitLSNState *waitLSNState;
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extern Size WaitLSNShmemSize(void);
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extern void WaitLSNShmemInit(void);
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extern void WaitLSNWakeup(WaitLSNType lsnType, XLogRecPtr currentLSN);
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extern void WaitLSNCleanup(void);
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extern WaitLSNResult WaitForLSN(WaitLSNType lsnType, XLogRecPtr targetLSN,
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int64 timeout);
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#endif /* XLOG_WAIT_H */
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