Shulou(Shulou.com)06/01 Report--

CheckPointCopy.nextXid) (gdb) 8876 LWLockAcquire (OidGenLock, LW_SHARED); (gdb) 8877 checkPoint.nextOid = ShmemVariableCache- > nextOid (gdb) p checkPoint$13 = {redo = 5521451392, ThisTimeLineID = 1, PrevTimeLineID = 1, fullPageWrites = true, nextXidEpoch = 0, nextXid = 2308, nextOid = 0, nextMulti = 0, nextMultiOffset = 0, oldestXid = 561, oldestXidDB = 16400, oldestMulti = 0, oldestMultiDB = 0, time = 1546933255, oldestCommitTsXid = 0, newestCommitTsXid = 0, oldestActiveXid = 0} (gdb) n8878 if (! shutdown) (gdb) 8879 checkPoint.nextOid + = ShmemVariableCache- > oidCount; (gdb) 8880 LWLockRelease (OidGenLock) (gdb) p * ShmemVariableCache$14 = {nextOid = 42575, oidCount = 8189, nextXid = 2308, oldestXid = 561, xidVacLimit = 200000561, xidWarnLimit = 2136484208, xidStopLimit = 2146484208, xidWrapLimit = 2147484208, oldestXidDB = 16400, oldestCommitTsXid = 0, newestCommitTsXid = 0, latestCompletedXid = 2307, oldestClogXid = 561} (gdb) n8882 MultiXactGetCheckptMulti (shutdown, (gdb))

Look at the checkpoint structure again

(gdb) p checkPoint$15 = {redo = 5521451392, ThisTimeLineID = 1, PrevTimeLineID = 1, fullPageWrites = true, nextXidEpoch = 0, nextXid = 2308, nextOid = 50764, nextMulti = 1, nextMultiOffset = 0, oldestXid = 561, oldestXidDB = 16400, oldestMulti = 1, oldestMultiDB = 16402, time = 1546933255, oldestCommitTsXid = 0, newestCommitTsXid = 0, oldestActiveXid = 0} (gdb)

End CRIT_SECTION

(gdb) 8896 END_CRIT_SECTION ()

Get virtual transaction ID (invalid information)

(gdb) n8927 vxids = GetVirtualXIDsDelayingChkpt (& nvxids); (gdb) 8928 if (nvxids > 0) (gdb) p vxids$16 = (VirtualTransactionId *) 0x2f4eb20 (gdb) p * vxids$17 = {backendId = 2139062143, localTransactionId = 2139062143} (gdb) p nvxids$18 = 0 (gdb) (gdb) n8935 pfree (vxids); (gdb)

Brush the data in the shared memory to disk and execute fsync

(gdb) 8937 CheckPointGuts (checkPoint.redo, flags); (gdb) p flags$19 = 44 (gdb) n8947 if (! shutdown & & XLogStandbyInfoActive ()) (gdb)

Enter critical section.

(gdb) n8950 START_CRIT_SECTION (); (gdb)

You can now insert checkpoint record into XLOG.

(gdb) 8955 XLogBeginInsert (); (gdb) n8956 XLogRegisterData ((char *) (& checkPoint), sizeof (checkPoint)); (gdb) 8957 recptr = XLogInsert (RM_XLOG_ID, (gdb) 8961 XLogFlush (recptr); (gdb) 8970 if (shutdown) (gdb))

Update the control file (pg_control), first record the REDO ptr of the previous checkpoint for UpdateCheckPointDistanceEstimate ()

(gdb) 8982 if (shutdown & & checkPoint.redo! = ProcLastRecPtr) (gdb) 8990 PriorRedoPtr = ControlFile- > checkPointCopy.redo; (gdb) 8995 LWLockAcquire (ControlFileLock, LW_EXCLUSIVE); (gdb) p ControlFile- > checkPointCopy.redo$20 = 5521450856 (gdb) n8996 if (shutdown) (gdb) 8998 ControlFile- > checkPoint = ProcLastRecPtr; (gdb) 8999 ControlFile- > checkPointCopy = checkPoint; (gdb) 9000 ControlFile- > time = (pg_time_t) time (NULL) (gdb) 9002 ControlFile- > minRecoveryPoint = InvalidXLogRecPtr; (gdb) 9003 ControlFile- > minRecoveryPointTLI = 0; (gdb) 9010 SpinLockAcquire (& XLogCtl- > ulsn_lck); (gdb) 9011 ControlFile- > unloggedLSN = XLogCtl- > unloggedLSN; (gdb) 9012 SpinLockRelease (& XLogCtl- > ulsn_lck); (gdb) 9014 UpdateControlFile (); (gdb) 9015 LWLockRelease (ControlFileLock); (gdb) 9018 SpinLockAcquire (& XLogCtl- > info_lck) (gdb) p * ControlFile$21 = {system_identifier = 6624362124887945794, pg_control_version = 1100, catalog_version_no = 201809051, state = DB_IN_PRODUCTION, time = 1546934255, checkPoint = 5521451392, checkPointCopy = {redo = 5521451392, ThisTimeLineID = 1, PrevTimeLineID = 1, fullPageWrites = true, nextXidEpoch = 0, nextXid = 2308, nextOid = 50764, nextMulti = 1, nextMultiOffset = 0, oldestXid = 561, oldestXidDB = 16400, oldestMulti = 1, oldestMultiDB = 16402, time = 1546933255, oldestCommitTsXid = 0, newestCommitTsXid = 0, oldestActiveXid = 0}, unloggedLSN = 1 MinRecoveryPoint = 0, minRecoveryPointTLI = 0, backupStartPoint = 0, backupEndPoint = 0, backupEndRequired = false, wal_level = 0, wal_log_hints = false, MaxConnections = 100, max_worker_processes = 8, max_prepared_xacts = 0, max_locks_per_xact = 64, track_commit_timestamp = false, maxAlign = 8, floatFormat = 1234567, blcksz = 8192, relseg_size = 131072, xlog_blcksz = 8192, xlog_seg_size = 16777216, nameDataLen = 64, indexMaxKeys = 32, toast_max_chunk_size = 1996, loblksize = 2048 Float4ByVal = true, float8ByVal = true, data_checksum_version = 0, mock_authentication_nonce = "\ 220\ 277\ 067Vg\ 003\ 205\ 232U {\ 177 h\ 216\ 271D\ 266\ 063 [\ = 6\ 365S\ tA\ 353\ 361w\ 301", crc = 930305687} (gdb)

Update the shared memory copy of checkpoint XID/epoch, exit critical section, and let smgr perform checkpoint finalization (such as deleting old files, etc.).

(gdb) n9019 XLogCtl- > ckptXidEpoch = checkPoint.nextXidEpoch; (gdb) 9020 XLogCtl- > ckptXid = checkPoint.nextXid; (gdb) 9021 SpinLockRelease (& XLogCtl- > info_lck); (gdb) 9027 END_CRIT_SECTION (); (gdb) 9032 smgrpostckpt (); (gdb)

Delete old log files that are no longer needed since the last checkpoint to prevent the disk that saved the xlog from filling up.

(gdb) n9038 if (PriorRedoPtr! = InvalidXLogRecPtr) (gdb) p PriorRedoPtr$23 = 5521450856 (gdb) n9039 UpdateCheckPointDistanceEstimate (RedoRecPtr-PriorRedoPtr); (gdb) 9045 XLByteToSeg (RedoRecPtr, _ logSegNo, wal_segment_size); (gdb) 9046 KeepLogSeg (recptr, & _ logSegNo); (gdb) p RedoRecPtr$24 = 5521451392 (gdb) p _ logSegNo$25 = 329 (gdb) p wal_segment_size$26 = 16777216 (gdb) n9047 _ logSegNo--; (gdb) 9048 RemoveOldXlogFiles (_ logSegNo, RedoRecPtr, recptr) (gdb) 9054 if (! shutdown) (gdb) p recptr$27 = 5521451504 (gdb)

Perform other related closing work

(gdb) n9055 PreallocXlogFiles (recptr); (gdb) 9064 if (! RecoveryInProgress ()) (gdb) 9065 TruncateSUBTRANS (GetOldestXmin (NULL, PROCARRAY_FLAGS_DEFAULT)); (gdb) 9068 LogCheckpointEnd (false); (gdb) 9070 TRACE_POSTGRESQL_CHECKPOINT_DONE (CheckpointStats.ckpt_bufs_written, (gdb) 9076 LWLockRelease (CheckpointLock); (gdb) 9077} (gdb))

Complete the call

(gdb) CheckpointerMain () at checkpointer.c:488488 ckpt_performed = true; (gdb)

DONE!

IV. Reference materials

Checkpointer.c

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