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Don't ERROR on PreallocXlogFiles() race condition. 

Before a restartpoint finishes PreallocXlogFiles(), a startup process
KeepFileRestoredFromArchive() call can unlink the preallocated segment.
If a CHECKPOINT sql command had elicited the restartpoint experiencing
the race condition, that sql command failed.  Moreover, the restartpoint
omitted its log_checkpoints message and some inessential resource
reclamation.  Prevent the ERROR by skipping open() of the segment.
Since these consequences are so minor, no back-patch.

Discussion: https://postgr.es/m/20210202151416.GB3304930@rfd.leadboat.com
This commit is contained in:
Noah Misch 2021-06-28 18:34:56 -07:00
parent 421484f79c
commit 2b3e4672f7
3 changed files with 58 additions and 27 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

79
src/backend/access/transam/xlog.c
View File

@ -2424,7 +2424,6 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
bool ispartialpage;
bool last_iteration;
bool finishing_seg;
bool added;
int curridx;
int npages;
int startidx;
@ -2490,7 +2489,7 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible)
wal_segment_size);
/* create/use new log file */
openLogFile = XLogFileInit(openLogSegNo, &added);
openLogFile = XLogFileInit(openLogSegNo);
ReserveExternalFD();
}
@ -3255,23 +3254,21 @@ XLogNeedsFlush(XLogRecPtr record)
}
/*
* Create a new XLOG file segment, or open a pre-existing one.
* Try to make a given XLOG file segment exist.
*
* logsegno: identify segment to be created/opened.
* logsegno: identify segment.
*
* *added: on return, true if this call raised the number of extant segments.
*
* Returns FD of opened file.
* path: on return, this char[MAXPGPATH] has the path to the logsegno file.
*
* Note: errors here are ERROR not PANIC because we might or might not be
* inside a critical section (eg, during checkpoint there is no reason to
* take down the system on failure). They will promote to PANIC if we are
* in a critical section.
* Returns -1 or FD of opened file. A -1 here is not an error; a caller
* wanting an open segment should attempt to open "path", which usually will
* succeed. (This is weird, but it's efficient for the callers.)
*/
int
XLogFileInit(XLogSegNo logsegno, bool *added)
static int
XLogFileInitInternal(XLogSegNo logsegno, bool *added, char *path)
{
char path[MAXPGPATH];
char tmppath[MAXPGPATH];
PGAlignedXLogBlock zbuffer;
XLogSegNo installed_segno;
@ -3424,26 +3421,53 @@ XLogFileInit(XLogSegNo logsegno, bool *added)
*/
max_segno = logsegno + CheckPointSegments;
if (InstallXLogFileSegment(&installed_segno, tmppath, true, max_segno))
{
*added = true;
elog(DEBUG2, "done creating and filling new WAL file");
}
else
{
/*
* No need for any more future segments, or InstallXLogFileSegment()
* failed to rename the file into place. If the rename failed, opening
* the file below will fail.
* failed to rename the file into place. If the rename failed, a
* caller opening the file may fail.
*/
unlink(tmppath);
elog(DEBUG2, "abandoned new WAL file");
}
return -1;
}
/*
* Create a new XLOG file segment, or open a pre-existing one.
*
* logsegno: identify segment to be created/opened.
*
* Returns FD of opened file.
*
* Note: errors here are ERROR not PANIC because we might or might not be
* inside a critical section (eg, during checkpoint there is no reason to
* take down the system on failure). They will promote to PANIC if we are
* in a critical section.
*/
int
XLogFileInit(XLogSegNo logsegno)
{
bool ignore_added;
char path[MAXPGPATH];
int fd;
fd = XLogFileInitInternal(logsegno, &ignore_added, path);
if (fd >= 0)
return fd;
/* Now open original target segment (might not be file I just made) */
fd = BasicOpenFile(path, O_RDWR | PG_BINARY | get_sync_bit(sync_method));
if (fd < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m", path)));
elog(DEBUG2, "done creating and filling new WAL file");
return fd;
}
@ -3903,6 +3927,15 @@ XLogFileClose(void)
* High-volume systems will be OK once they've built up a sufficient set of
* recycled log segments, but the startup transient is likely to include
* a lot of segment creations by foreground processes, which is not so good.
*
* XLogFileInitInternal() can ereport(ERROR). All known causes indicate big
* trouble; for example, a full filesystem is one cause. The checkpoint WAL
* and/or ControlFile updates already completed. If a RequestCheckpoint()
* initiated the present checkpoint and an ERROR ends this function, the
* command that called RequestCheckpoint() fails. That's not ideal, but it's
* not worth contorting more functions to use caller-specified elevel values.
* (With or without RequestCheckpoint(), an ERROR forestalls some inessential
* reporting and resource reclamation.)
*/
static void
PreallocXlogFiles(XLogRecPtr endptr)
@ -3910,6 +3943,7 @@ PreallocXlogFiles(XLogRecPtr endptr)
XLogSegNo _logSegNo;
int lf;
bool added;
char path[MAXPGPATH];
uint64 offset;
XLByteToPrevSeg(endptr, _logSegNo, wal_segment_size);
@ -3917,8 +3951,9 @@ PreallocXlogFiles(XLogRecPtr endptr)
if (offset >= (uint32) (0.75 * wal_segment_size))
{
_logSegNo++;
lf = XLogFileInit(_logSegNo, &added);
close(lf);
lf = XLogFileInitInternal(_logSegNo, &added, path);
if (lf >= 0)
close(lf);
if (added)
CheckpointStats.ckpt_segs_added++;
}
@ -5214,7 +5249,6 @@ BootStrapXLOG(void)
XLogLongPageHeader longpage;
XLogRecord *record;
char *recptr;
bool added;
uint64 sysidentifier;
struct timeval tv;
pg_crc32c crc;
@ -5311,7 +5345,7 @@ BootStrapXLOG(void)
record->xl_crc = crc;
/* Create first XLOG segment file */
openLogFile = XLogFileInit(1, &added);
openLogFile = XLogFileInit(1);
/*
* We needn't bother with Reserve/ReleaseExternalFD here, since we'll
@ -5617,10 +5651,9 @@ exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog)
* The switch happened at a segment boundary, so just create the next
* segment on the new timeline.
*/
bool added;
int fd;
fd = XLogFileInit(startLogSegNo, &added);
fd = XLogFileInit(startLogSegNo);
if (close(fd) != 0)
{

4
src/backend/replication/walreceiver.c
View File

@ -885,8 +885,6 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
if (recvFile < 0 || !XLByteInSeg(recptr, recvSegNo, wal_segment_size))
{
bool added;
/*
* fsync() and close current file before we switch to next one. We
* would otherwise have to reopen this file to fsync it later
@ -923,7 +921,7 @@ XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
/* Create/use new log file */
XLByteToSeg(recptr, recvSegNo, wal_segment_size);
recvFile = XLogFileInit(recvSegNo, &added);
recvFile = XLogFileInit(recvSegNo);
recvFileTLI = ThisTimeLineID;
}

2
src/include/access/xlog.h
View File

@ -296,7 +296,7 @@ extern XLogRecPtr XLogInsertRecord(struct XLogRecData *rdata,
extern void XLogFlush(XLogRecPtr RecPtr);
extern bool XLogBackgroundFlush(void);
extern bool XLogNeedsFlush(XLogRecPtr RecPtr);
extern int XLogFileInit(XLogSegNo segno, bool *added);
extern int XLogFileInit(XLogSegNo segno);
extern int XLogFileOpen(XLogSegNo segno);
extern void CheckXLogRemoved(XLogSegNo segno, TimeLineID tli);