PostgreSQL start recovery Read checkpoint record failed condition

1、首先读取ControlFile->checkPoint指向的checkpoint2、如果读取失败，slave直接abort退出，master再次读取ControlFile->prevCheckPoint指向的checkpointStartupXLOG-> |--checkPointLoc = ControlFile->checkPoint; |--record = ReadCheckpointRecord(xlogreader, checkPointLoc, 1, true): |-- if (record != NULL){ ... }else if (StandbyMode){ ereport(PANIC,(errmsg("could not locate a valid checkpoint record"))); }else{ checkPointLoc = ControlFile->prevCheckPoint; record = ReadCheckpointRecord(xlogreader, checkPointLoc, 2, true); if (record != NULL){ InRecovery = true;//标记下面进入recovery }else{ ereport(PANIC,(errmsg("could not locate a valid checkpoint record"))); } }

One, then what condition reads the checkpoint record Record==null?

1、ControlFile->checkPoint % XLOG_BLCKSZ < SizeOfXLogShortPHD2、ReadRecord(xlogreader, ControlFile->checkPoint, LOG, true)返回NULL3、ReadRecord读到的record!=NULL && record->xl_rmid != RM_XLOG_ID4、ReadRecord读到的record!=NULL && info != XLOG_CHECKPOINT_SHUTDOWN && info != XLOG_CHECKPOINT_ONLINE5、ReadRecord读到的record!=NULL && record->xl_tot_len != SizeOfXLogRecord + SizeOfXLogRecordDataHeaderShort + sizeof(CheckPoint)

Second, the Readrecord function returns null condition

ReadRecord(xlogreader, ControlFile->checkPoint, LOG, true)    |--record = XLogReadRecord(xlogreader, ControlFile->checkPoint, &errormsg);    |-- 2.1 record==NULL && ！StandbyMode    |-- 2.2 record!=NULL && !tliInHistory(xlogreader->latestPageTLI, expectedTLEs)    /*-----    note:只要读取了一页xlog,就会赋值为该页第一个记录的时间线    XLogReaderValidatePageHeader        -->xlogreader->latestPageTLI=hdr->xlp_tli;    ------*/

Three, Xlogreadrecord read checkpoint return null condition?

Xlogreadrecord (Xlogreader, Controlfile->checkpoint, &errormsg) targetpageptr = ControlFile->checkPoint-(    Controlfile->checkpoint% Xlog_blcksz);    Targetrecoff = controlfile->checkpoint% Xlog_blcksz;    Readoff = Readpageinternal (State,targetpageptr, Min (Targetrecoff + Sizeofxlogrecord, Xlog_blcksz));    Pageheadersize = Xlogpageheadersize ((xlogpageheader) state->readbuf);    Record = (Xlogrecord *) (state->readbuf + recptr% Xlog_blcksz);    Total_len = record->xl_tot_len; -------------1, Readoff < 0 2, 0< Targetrecoff < Pageheadersize 3, ((Xlogpageheader) state->readbuf)-& Gt;xlp_info & Xlp_first_is_contrecord) && Targetrecoff = = pageheadersize The page header has a record of the spread and checkpoint-positioned offset Move exactly at the end of the page 4, Targetrecoff <= Xlog_blcksz-sizeofxlogrecord &&! Validxlogrecordheader (state, Controlfile->checkpoint, State->readrecptr, record,randaccess)---(record-> Xl_tot_len < Sizeofxlogrecord | | RecorD->xl_rmid > rm_max_id | | Record->xl_prev! = state->readrecptr) 5, Targetrecoff > Xlog_blcksz-sizeofxlogrecord && total_len &lt ; Sizeofxlogrecord 6, Total_len > State->readrecordbufsize &&!allocate_recordbuf (state, Total_len) once If the record is corrupted and the length of the Total_len is very large, then the allocate_recordbuf extension state->readbuf may be required, so the checksum of the abort record for the allocation failure will need to wait for the full record to be read before verifying the----- --------

Iii. Readpageinternal returned Readoff returns less than 0 of the condition

ReadPageInternal(state,targetPagePtr, Min(targetRecOff + SizeOfXLogRecord, XLOG_BLCKSZ))    1、第一次read wal文件，readLen = state->read_page：读取第一页。readLen < 0    2、readLen>0 && !XLogReaderValidatePageHeader(state, targetSegmentPtr, state->readBuf)    --    3、读取checkpoint所在页readLen = state->read_page: readLen < 0    4、readLen > 0 && readLen <= SizeOfXLogShortPHD    5、!XLogReaderValidatePageHeader(state, pageptr, (char *) hdr)

Iv. when Xlogpageread return value <0?

/*    1、WaitForWALToBecomeAvailable open失败    2、lseek 失败 && ！StandbyMode    3、read失败 && ！StandbyMode    4、校验page头失败 && ！StandbyMode    如果是StandbyMode，则会重新retry->WaitForWALToBecomeAvailable,切换日志源进行open    */    !WaitForWALToBecomeAvailable(targetPagePtr + reqLen,private->randAccess,1,targetRecPtr)//open    |-- return -1    readOff = targetPageOff;    if (lseek(readFile, (off_t) readOff, SEEK_SET) < 0){        ！StandbyMode:: return -1    }    if (read(readFile, readBuf, XLOG_BLCKSZ) != XLOG_BLCKSZ){        ！StandbyMode:: return -1    }    XLogReaderValidatePageHeader(xlogreader, targetPagePtr, readBuf)    ！StandbyMode:: return -1

V. When does waitforwaltobecomeavailable return false?

--XLOG_FROM_ARCHIVE | XLOG_FROM_PG_WAL    1、先XLogFileReadAnyTLI open日志：        1、遍历时间线列表里的每一个时间线，从最新的开始        2、当读取checkpoint的时候，source是XLOG_FROM_ANY        3、先找归档的日志进行open；如果open失败再找WAL日志进行open        4、如果都没有open成功，则向前找时间线，open前一个时间线segno和文件号相同的文件进行open        5、open成功后expectedTLEs被赋值为当前时间线列表的所有值    2、如果open失败，则切换日志源：XLOG_FROM_ARCHIVE | XLOG_FROM_PG_WAL -> XLOG_FROM_STREAM    3、切换日志源后，XLOG_FROM_ARCHIVE | XLOG_FROM_PG_WAL 则：       slave && promote ：return false       !StandbyMode：return false    --XLOG_FROM_STREAM    1、!WalRcvStreaming()即receiver进程挂了，切换日志源    2、CheckForStandbyTrigger()切换日志源    3、XLOG_FROM_STREAM->XLOG_FROM_ARCHIVE

PostgreSQL start recovery Read checkpoint record failed condition