From 34c0ae891de7dae3b84de33795c5d0521ccc0a88 Mon Sep 17 00:00:00 2001 From: Antonin Houska Date: Tue, 12 Nov 2019 11:51:14 +0100 Subject: [PATCH 1/2] Use only xlogreader.c:XLogRead() The implementations in xlogutils.c and walsender.c are just renamed now, to be removed by the following diff. --- src/backend/access/transam/xlogreader.c | 121 ++++++++++++++++++++ src/backend/access/transam/xlogutils.c | 94 ++++++++++++++-- src/backend/replication/walsender.c | 143 +++++++++++++++++++++++- src/bin/pg_waldump/pg_waldump.c | 63 ++++++++++- src/include/access/xlogreader.h | 37 ++++++ src/include/access/xlogutils.h | 1 + 6 files changed, 441 insertions(+), 18 deletions(-) diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c index 7f24f0cb95..006c6298c9 100644 --- a/src/backend/access/transam/xlogreader.c +++ b/src/backend/access/transam/xlogreader.c @@ -17,6 +17,8 @@ */ #include "postgres.h" +#include + #include "access/transam.h" #include "access/xlog_internal.h" #include "access/xlogreader.h" @@ -27,6 +29,7 @@ #ifndef FRONTEND #include "miscadmin.h" +#include "pgstat.h" #include "utils/memutils.h" #endif @@ -1015,6 +1018,124 @@ out: #endif /* FRONTEND */ +/* + * Read 'count' bytes from WAL fetched from timeline 'tli' into 'buf', + * starting at location 'startptr'. 'seg' is the last segment used, + * 'openSegment' is a callback to open the next segment and 'segcxt' is + * additional segment info that does not fit into 'seg'. + * + * 'errinfo' should point to XLogReadError structure which will receive error + * details in case the read fails. + * + * Returns true if succeeded, false if failed. + * + * XXX probably this should be improved to suck data directly from the + * WAL buffers when possible. + */ +bool +XLogRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli, + WALOpenSegment *seg, WALSegmentContext *segcxt, + WALSegmentOpen openSegment, WALReadError *errinfo) +{ + char *p; + XLogRecPtr recptr; + Size nbytes; + + p = buf; + recptr = startptr; + nbytes = count; + + while (nbytes > 0) + { + uint32 startoff; + int segbytes; + int readbytes; + + startoff = XLogSegmentOffset(recptr, segcxt->ws_segsize); + + if (seg->ws_file < 0 || + !XLByteInSeg(recptr, seg->ws_segno, segcxt->ws_segsize) || + tli != seg->ws_tli) + { + XLogSegNo nextSegNo; + + /* Switch to another logfile segment */ + if (seg->ws_file >= 0) + close(seg->ws_file); + + XLByteToSeg(recptr, nextSegNo, segcxt->ws_segsize); + + /* Open the next segment in the caller's way. */ + openSegment(nextSegNo, segcxt, &tli, &seg->ws_file); + + /* Update the current segment info. */ + seg->ws_tli = tli; + seg->ws_segno = nextSegNo; + seg->ws_off = 0; + } + + /* Need to seek in the file? */ + if (seg->ws_off != startoff) + { + /* + * Update ws_off unconditionally, it will be useful for error + * message too. + */ + seg->ws_off = startoff; + + if (lseek(seg->ws_file, (off_t) startoff, SEEK_SET) < 0) + { + errinfo->xlr_seek = true; + errinfo->xlr_errno = errno; + errinfo->xlr_req = 0; + errinfo->xlr_read = 0; + errinfo->xlr_seg = seg; + return false; + } + } + + /* How many bytes are within this segment? */ + if (nbytes > (segcxt->ws_segsize - seg->ws_off)) + segbytes = segcxt->ws_segsize - seg->ws_off; + else + segbytes = nbytes; + +#ifndef FRONTEND + pgstat_report_wait_start(WAIT_EVENT_WAL_READ); +#endif + + /* + * Failure to read the data does not necessarily imply non-zero errno. + * Set it to zero so that caller can distinguish the failure that does + * not affect errno. + */ + errno = 0; + + readbytes = read(seg->ws_file, p, segbytes); + +#ifndef FRONTEND + pgstat_report_wait_end(); +#endif + + if (readbytes <= 0) + { + errinfo->xlr_seek = false; + errinfo->xlr_errno = errno; + errinfo->xlr_req = segbytes; + errinfo->xlr_read = readbytes; + errinfo->xlr_seg = seg; + return false; + } + + /* Update state for read */ + recptr += readbytes; + nbytes -= readbytes; + p += readbytes; + } + + return true; +} + /* ---------------------------------------- * Functions for decoding the data and block references in a record. * ---------------------------------------- diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c index 5f1e5ba75d..18e436f4fd 100644 --- a/src/backend/access/transam/xlogutils.c +++ b/src/backend/access/transam/xlogutils.c @@ -653,8 +653,8 @@ XLogTruncateRelation(RelFileNode rnode, ForkNumber forkNum, * frontend). Probably these should be merged at some point. */ static void -XLogRead(char *buf, int segsize, TimeLineID tli, XLogRecPtr startptr, - Size count) +XLogReadOld(char *buf, int segsize, TimeLineID tli, XLogRecPtr startptr, + Size count) { char *p; XLogRecPtr recptr; @@ -896,6 +896,37 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa } } +/* + * Callback for XLogRead() to open the next segment. + */ +static void +wal_segment_open(XLogSegNo nextSegNo, WALSegmentContext *segcxt, + TimeLineID *tli_p, int *file_p) +{ + TimeLineID tli = *tli_p; + char path[MAXPGPATH]; + int file; + + XLogFilePath(path, tli, nextSegNo, segcxt->ws_segsize); + file = BasicOpenFile(path, O_RDONLY | PG_BINARY); + + if (file < 0) + { + if (errno == ENOENT) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("requested WAL segment %s has already been removed", + path))); + else + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not open file \"%s\": %m", + path))); + } + + *file_p = file; +} + /* * read_page callback for reading local xlog files * @@ -913,7 +944,9 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, { XLogRecPtr read_upto, loc; + TimeLineID tli; int count; + WALReadError errinfo; loc = targetPagePtr + reqLen; @@ -932,7 +965,7 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, read_upto = GetFlushRecPtr(); else read_upto = GetXLogReplayRecPtr(&ThisTimeLineID); - state->seg.ws_tli = ThisTimeLineID; + tli = ThisTimeLineID; /* * Check which timeline to get the record from. @@ -982,14 +1015,14 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, read_upto = state->currTLIValidUntil; /* - * Setting ws_tli to our wanted record's TLI is slightly wrong; - * the page might begin on an older timeline if it contains a - * timeline switch, since its xlog segment will have been copied - * from the prior timeline. This is pretty harmless though, as - * nothing cares so long as the timeline doesn't go backwards. We - * should read the page header instead; FIXME someday. + * Setting tli to our wanted record's TLI is slightly wrong; the + * page might begin on an older timeline if it contains a timeline + * switch, since its xlog segment will have been copied from the + * prior timeline. This is pretty harmless though, as nothing + * cares so long as the timeline doesn't go backwards. We should + * read the page header instead; FIXME someday. */ - state->seg.ws_tli = state->currTLI; + tli = state->currTLI; /* No need to wait on a historical timeline */ break; @@ -1020,9 +1053,46 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, * as 'count', read the whole page anyway. It's guaranteed to be * zero-padded up to the page boundary if it's incomplete. */ - XLogRead(cur_page, state->segcxt.ws_segsize, state->seg.ws_tli, targetPagePtr, - XLOG_BLCKSZ); + if (!XLogRead(cur_page, targetPagePtr, XLOG_BLCKSZ, tli, &state->seg, + &state->segcxt, wal_segment_open, &errinfo)) + WALReadRaiseError(&errinfo); /* number of valid bytes in the buffer */ return count; } + +/* + * Backend-specific convenience code to handle read errors encountered by + * XLogRead(). + */ +void +WALReadRaiseError(WALReadError *errinfo) +{ + WALOpenSegment *seg = errinfo->xlr_seg; + char *fname = XLogFileNameP(seg->ws_tli, seg->ws_segno); + + if (errinfo->xlr_seek) + { + errno = errinfo->xlr_errno; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not seek in log segment %s to offset %u: %m", + fname, seg->ws_off))); + } + else if (errinfo->xlr_read < 0) + { + errno = errinfo->xlr_errno; + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not read from log segment %s, offset %u, length %zu: %m", + fname, seg->ws_off, (Size) errinfo->xlr_req))); + } + else if (errinfo->xlr_read == 0) + { + ereport(ERROR, + (errcode(ERRCODE_DATA_CORRUPTED), + errmsg("could not read from log segment %s, offset %u: read %d of %zu", + fname, seg->ws_off, errinfo->xlr_read, + (Size) errinfo->xlr_req))); + } +} diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c index 7f5671504f..92a539aa5c 100644 --- a/src/backend/replication/walsender.c +++ b/src/backend/replication/walsender.c @@ -248,9 +248,13 @@ static void LagTrackerWrite(XLogRecPtr lsn, TimestampTz local_flush_time); static TimeOffset LagTrackerRead(int head, XLogRecPtr lsn, TimestampTz now); static bool TransactionIdInRecentPast(TransactionId xid, uint32 epoch); -static void XLogRead(WALSegmentContext *segcxt, char *buf, XLogRecPtr startptr, Size count); +static void WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt, + TimeLineID *tli_p, int *file_p); +static void XLogReadOld(WALSegmentContext *segcxt, char *buf, + XLogRecPtr startptr, Size count); + /* Initialize walsender process before entering the main command loop */ void InitWalSender(void) @@ -766,6 +770,8 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req { XLogRecPtr flushptr; int count; + WALReadError errinfo; + XLogSegNo segno; XLogReadDetermineTimeline(state, targetPagePtr, reqLen); sendTimeLineIsHistoric = (state->currTLI != ThisTimeLineID); @@ -786,7 +792,27 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req count = flushptr - targetPagePtr; /* part of the page available */ /* now actually read the data, we know it's there */ - XLogRead(sendCxt, cur_page, targetPagePtr, XLOG_BLCKSZ); + if (!XLogRead(cur_page, + targetPagePtr, + XLOG_BLCKSZ, + sendSeg->ws_tli, /* Pass the current TLI because only + * WalSndSegmentOpen controls whether new + * TLI is needed. */ + sendSeg, + sendCxt, + WalSndSegmentOpen, + &errinfo)) + WALReadRaiseError(&errinfo); + + /* + * After reading into the buffer, check that what we read was valid. We do + * this after reading, because even though the segment was present when we + * opened it, it might get recycled or removed while we read it. The + * read() succeeds in that case, but the data we tried to read might + * already have been overwritten with new WAL records. + */ + XLByteToSeg(targetPagePtr, segno, sendCxt->ws_segsize); + CheckXLogRemoved(segno, sendSeg->ws_tli); return count; } @@ -2362,7 +2388,7 @@ WalSndKill(int code, Datum arg) * more than one. */ static void -XLogRead(WALSegmentContext *segcxt, char *buf, XLogRecPtr startptr, Size count) +XLogReadOld(WALSegmentContext *segcxt, char *buf, XLogRecPtr startptr, Size count) { char *p; XLogRecPtr recptr; @@ -2535,6 +2561,71 @@ retry: } } +/* + * Callback for XLogRead() to open the next segment. + */ +void +WalSndSegmentOpen(XLogSegNo nextSegNo, WALSegmentContext *segcxt, + TimeLineID *tli_p, int *file_p) +{ + char path[MAXPGPATH]; + + /*------- + * When reading from a historic timeline, and there is a timeline switch + * within this segment, read from the WAL segment belonging to the new + * timeline. + * + * For example, imagine that this server is currently on timeline 5, and + * we're streaming timeline 4. The switch from timeline 4 to 5 happened at + * 0/13002088. In pg_wal, we have these files: + * + * ... + * 000000040000000000000012 + * 000000040000000000000013 + * 000000050000000000000013 + * 000000050000000000000014 + * ... + * + * In this situation, when requested to send the WAL from segment 0x13, on + * timeline 4, we read the WAL from file 000000050000000000000013. Archive + * recovery prefers files from newer timelines, so if the segment was + * restored from the archive on this server, the file belonging to the old + * timeline, 000000040000000000000013, might not exist. Their contents are + * equal up to the switchpoint, because at a timeline switch, the used + * portion of the old segment is copied to the new file. ------- + */ + *tli_p = sendTimeLine; + if (sendTimeLineIsHistoric) + { + XLogSegNo endSegNo; + + XLByteToSeg(sendTimeLineValidUpto, endSegNo, segcxt->ws_segsize); + if (sendSeg->ws_segno == endSegNo) + *tli_p = sendTimeLineNextTLI; + } + + XLogFilePath(path, *tli_p, nextSegNo, segcxt->ws_segsize); + *file_p = BasicOpenFile(path, O_RDONLY | PG_BINARY); + + if (*file_p < 0) + { + /* + * If the file is not found, assume it's because the standby asked for + * a too old WAL segment that has already been removed or recycled. + */ + if (errno == ENOENT) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("requested WAL segment %s has already been removed", + XLogFileNameP(*tli_p, nextSegNo)))); + else + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not open file \"%s\": %m", + path))); + } +} + /* * Send out the WAL in its normal physical/stored form. * @@ -2552,6 +2643,8 @@ XLogSendPhysical(void) XLogRecPtr startptr; XLogRecPtr endptr; Size nbytes; + XLogSegNo segno; + WALReadError errinfo; /* If requested switch the WAL sender to the stopping state. */ if (got_STOPPING) @@ -2767,7 +2860,49 @@ XLogSendPhysical(void) * calls. */ enlargeStringInfo(&output_message, nbytes); - XLogRead(sendCxt, &output_message.data[output_message.len], startptr, nbytes); + +retry: + if (!XLogRead(&output_message.data[output_message.len], + startptr, + nbytes, + sendSeg->ws_tli, /* Pass the current TLI because only + * WalSndSegmentOpen controls whether new + * TLI is needed. */ + sendSeg, + sendCxt, + WalSndSegmentOpen, + &errinfo)) + WALReadRaiseError(&errinfo); + + /* See logical_read_xlog_page(). */ + XLByteToSeg(startptr, segno, sendCxt->ws_segsize); + CheckXLogRemoved(segno, sendSeg->ws_tli); + + /* + * During recovery, the currently-open WAL file might be replaced with the + * file of the same name retrieved from archive. So we always need to + * check what we read was valid after reading into the buffer. If it's + * invalid, we try to open and read the file again. + */ + if (am_cascading_walsender) + { + WalSnd *walsnd = MyWalSnd; + bool reload; + + SpinLockAcquire(&walsnd->mutex); + reload = walsnd->needreload; + walsnd->needreload = false; + SpinLockRelease(&walsnd->mutex); + + if (reload && sendSeg->ws_file >= 0) + { + close(sendSeg->ws_file); + sendSeg->ws_file = -1; + + goto retry; + } + } + output_message.len += nbytes; output_message.data[output_message.len] = '\0'; diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c index 1524e5eb1e..c0c2590d56 100644 --- a/src/bin/pg_waldump/pg_waldump.c +++ b/src/bin/pg_waldump/pg_waldump.c @@ -280,6 +280,46 @@ identify_target_directory(char *directory, char *fname) return NULL; /* not reached */ } +static void +WALDumpOpenSegment(XLogSegNo nextSegNo, WALSegmentContext *segcxt, + TimeLineID *tli_p, int *file_p) +{ + TimeLineID tli = *tli_p; + char fname[MAXPGPATH]; + int tries; + + XLogFileName(fname, tli, nextSegNo, segcxt->ws_segsize); + + /* + * In follow mode there is a short period of time after the server has + * written the end of the previous file before the new file is available. + * So we loop for 5 seconds looking for the file to appear before giving + * up. + */ + for (tries = 0; tries < 10; tries++) + { + *file_p = open_file_in_directory(segcxt->ws_dir, fname); + if (*file_p >= 0) + break; + if (errno == ENOENT) + { + int save_errno = errno; + + /* File not there yet, try again */ + pg_usleep(500 * 1000); + + errno = save_errno; + continue; + } + /* Any other error, fall through and fail */ + break; + } + + if (*file_p < 0) + fatal_error("could not find file \"%s\": %s", + fname, strerror(errno)); +} + /* * Read count bytes from a segment file in the specified directory, for the * given timeline, containing the specified record pointer; store the data in @@ -411,6 +451,7 @@ XLogDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen, { XLogDumpPrivate *private = state->private_data; int count = XLOG_BLCKSZ; + WALReadError errinfo; if (private->endptr != InvalidXLogRecPtr) { @@ -425,8 +466,26 @@ XLogDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen, } } - XLogDumpXLogRead(state->segcxt.ws_dir, private->timeline, targetPagePtr, - readBuff, count); + if (!XLogRead(readBuff, targetPagePtr, count, private->timeline, + &state->seg, &state->segcxt, WALDumpOpenSegment, &errinfo)) + { + WALOpenSegment *seg = errinfo.xlr_seg; + char fname[MAXPGPATH]; + + XLogFileName(fname, seg->ws_tli, seg->ws_segno, + state->segcxt.ws_segsize); + + if (errinfo.xlr_seek) + fatal_error("could not seek in file %s to offset %u: %s", + fname, seg->ws_off, strerror(errinfo.xlr_errno)); + else if (errinfo.xlr_errno != 0) + fatal_error("could not read in file %s, offset %u, length %zu: %s", + fname, seg->ws_off, (Size) errinfo.xlr_req, + strerror(errinfo.xlr_errno)); + else + fatal_error("could not read in file %s, offset %u: length: %zu", + fname, seg->ws_off, (Size) errinfo.xlr_req); + } return count; } diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h index 1bbee386e8..02d1514429 100644 --- a/src/include/access/xlogreader.h +++ b/src/include/access/xlogreader.h @@ -218,6 +218,26 @@ extern XLogReaderState *XLogReaderAllocate(int wal_segment_size, extern void XLogReaderFree(XLogReaderState *state); /* Initialize supporting structures */ +/* + * Callback to open the specified WAL segment for reading. + * + * "nextSegNo" is the number of the segment to be opened. + * + * "segcxt" is additional information about the segment. + * + * "tli_p" is an input/output argument. XLogRead() uses it to pass the + * timeline in which the new segment should be found, but the callback can use + * it to return the TLI that it actually opened. + * + * "file_p" points to an address the segment file descriptor should be stored + * at. + * + * BasicOpenFile() is the preferred way to open the segment file in backend + * code, whereas open(2) should be used in frontend. + */ +typedef void (*WALSegmentOpen) (XLogSegNo nextSegNo, WALSegmentContext *segcxt, + TimeLineID *tli_p, int *file_p); + extern void WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt, int segsize, const char *waldir); @@ -232,6 +252,23 @@ extern bool XLogReaderValidatePageHeader(XLogReaderState *state, #ifdef FRONTEND extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr); #endif /* FRONTEND */ +/* + * Error information that both backend and frontend caller can process. + */ +typedef struct WALReadError +{ + bool xlr_seek; /* Error during lseek() ? */ + int xlr_errno; /* errno set by the last read() / lseek() */ + int xlr_read; /* Bytes read by the last read(). */ + int xlr_req; /* Bytes requested to be read. */ + WALOpenSegment *xlr_seg; /* Segment we tried to read from. */ +} WALReadError; + +extern bool XLogRead(char *buf, XLogRecPtr startptr, Size count, + TimeLineID tli, WALOpenSegment *seg, + WALSegmentContext *segcxt, WALSegmentOpen openSegment, + WALReadError *errinfo); + /* Functions for decoding an XLogRecord */ extern bool DecodeXLogRecord(XLogReaderState *state, XLogRecord *record, diff --git a/src/include/access/xlogutils.h b/src/include/access/xlogutils.h index 2df98e45b2..1ffc765c6a 100644 --- a/src/include/access/xlogutils.h +++ b/src/include/access/xlogutils.h @@ -54,4 +54,5 @@ extern int read_local_xlog_page(XLogReaderState *state, extern void XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength); +void WALReadRaiseError(WALReadError *errinfo); #endif -- 2.20.1