/*
* Read 'count' bytes from WAL into 'buf', starting at location 'startptr'
*
* XXX probably this should be improved to suck data directly from the
* WAL buffers when possible.
*
* Will open, and keep open, one WAL segment stored in the global file
* descriptor sendFile. This means if XLogRead is used once, there will
* always be one descriptor left open until the process ends, but never
* more than one.
*/
void
XLogRead(char *buf, XLogRecPtr startptr, Size count)
{
char *p;
XLogRecPtr recptr;
Size nbytes;
uint32 lastRemovedLog;
uint32 lastRemovedSeg;
uint32 log;
uint32 seg;
retry:
p = buf;
recptr = startptr;
nbytes = count;
while (nbytes > 0)
{
uint32 startoff;
int segbytes;
int readbytes;
startoff = recptr.xrecoff % XLogSegSize;
if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
{
char path[MAXPGPATH];
/* Switch to another logfile segment */
if (sendFile >= 0)
close(sendFile);
XLByteToSeg(recptr, sendId, sendSeg);
XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
if (sendFile < 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)
{
char filename[MAXFNAMELEN];
XLogFileName(filename, ThisTimeLineID, sendId, sendSeg);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
filename)));
}
else
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
path, sendId, sendSeg)));
}
sendOff = 0;
}
/* Need to seek in the file? */
if (sendOff != startoff)
{
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in log file %u, segment %u to offset %u: %m",
sendId, sendSeg, startoff)));
sendOff = startoff;
}
/* How many bytes are within this segment? */
if (nbytes > (XLogSegSize - startoff))
segbytes = XLogSegSize - startoff;
else
segbytes = nbytes;
readbytes = read(sendFile, p, segbytes);
if (readbytes <= 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from log file %u, segment %u, offset %u, "
"length %lu: %m",
sendId, sendSeg, sendOff, (unsigned long) segbytes)));
/* Update state for read */
XLByteAdvance(recptr, readbytes);
sendOff += readbytes;
nbytes -= readbytes;
p += readbytes;
}
/*
* 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.
*/
XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);
XLByteToSeg(startptr, log, seg);
if (log < lastRemovedLog ||
(log == lastRemovedLog && seg <= lastRemovedSeg))
{
char filename[MAXFNAMELEN];
XLogFileName(filename, ThisTimeLineID, log, seg);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
filename)));
}
/*
* 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)
{
/* use volatile pointer to prevent code rearrangement */
volatile WalSnd *walsnd = MyWalSnd;
bool reload;
SpinLockAcquire(&walsnd->mutex);
reload = walsnd->needreload;
walsnd->needreload = false;
SpinLockRelease(&walsnd->mutex);
if (reload && sendFile >= 0)
{
close(sendFile);
sendFile = -1;
goto retry;
}
}
}
/*
* Write XLOG data to disk.
*/
static void
XLogWalRcvWrite(char *buf, Size nbytes, XLogRecPtr recptr)
{
int startoff;
int byteswritten;
while (nbytes > 0)
{
int segbytes;
if (recvFile < 0 || !XLByteInSeg(recptr, recvId, recvSeg))
{
bool use_existent;
/*
* fsync() and close current file before we switch to next one. We
* would otherwise have to reopen this file to fsync it later
*/
if (recvFile >= 0)
{
XLogWalRcvFlush();
/*
* XLOG segment files will be re-read by recovery in startup
* process soon, so we don't advise the OS to release cache
* pages associated with the file like XLogFileClose() does.
*/
if (close(recvFile) != 0)
ereport(PANIC,
(errcode_for_file_access(),
errmsg("could not close log file %u, segment %u: %m",
recvId, recvSeg)));
}
recvFile = -1;
/* Create/use new log file */
XLByteToSeg(recptr, recvId, recvSeg);
use_existent = true;
recvFile = XLogFileInit(recvId, recvSeg, &use_existent, true);
recvOff = 0;
}
/* Calculate the start offset of the received logs */
startoff = recptr.xrecoff % XLogSegSize;
if (startoff + nbytes > XLogSegSize)
segbytes = XLogSegSize - startoff;
else
segbytes = nbytes;
/* Need to seek in the file? */
if (recvOff != startoff)
{
if (lseek(recvFile, (off_t) startoff, SEEK_SET) < 0)
ereport(PANIC,
(errcode_for_file_access(),
errmsg("could not seek in log file %u, "
"segment %u to offset %u: %m",
recvId, recvSeg, startoff)));
recvOff = startoff;
}
/* OK to write the logs */
errno = 0;
byteswritten = write(recvFile, buf, segbytes);
if (byteswritten <= 0)
{
/* if write didn't set errno, assume no disk space */
if (errno == 0)
errno = ENOSPC;
ereport(PANIC,
(errcode_for_file_access(),
errmsg("could not write to log file %u, segment %u "
"at offset %u, length %lu: %m",
recvId, recvSeg,
recvOff, (unsigned long) segbytes)));
}
/* Update state for write */
XLByteAdvance(recptr, byteswritten);
recvOff += byteswritten;
nbytes -= byteswritten;
buf += byteswritten;
LogstreamResult.Write = recptr;
}
}
/*
* Read 'nbytes' bytes from WAL into 'buf', starting at location 'recptr'
*
* XXX probably this should be improved to suck data directly from the
* WAL buffers when possible.
*
* Will open, and keep open, one WAL segment stored in the global file
* descriptor sendFile. This means if XLogRead is used once, there will
* always be one descriptor left open until the process ends, but never
* more than one.
*/
void
XLogRead(char *buf, XLogRecPtr recptr, Size nbytes)
{
XLogRecPtr startRecPtr = recptr;
char path[MAXPGPATH];
uint32 lastRemovedLog;
uint32 lastRemovedSeg;
uint32 log;
uint32 seg;
while (nbytes > 0)
{
uint32 startoff;
int segbytes;
int readbytes;
startoff = recptr.xrecoff % XLogSegSize;
if (sendFile < 0 || !XLByteInSeg(recptr, sendId, sendSeg))
{
/* Switch to another logfile segment */
if (sendFile >= 0)
close(sendFile);
XLByteToSeg(recptr, sendId, sendSeg);
XLogFilePath(path, ThisTimeLineID, sendId, sendSeg);
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
if (sendFile < 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)
{
char filename[MAXFNAMELEN];
XLogFileName(filename, ThisTimeLineID, sendId, sendSeg);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
filename)));
}
else
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\" (log file %u, segment %u): %m",
path, sendId, sendSeg)));
}
sendOff = 0;
}
/* Need to seek in the file? */
if (sendOff != startoff)
{
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in log file %u, segment %u to offset %u: %m",
sendId, sendSeg, startoff)));
sendOff = startoff;
}
/* How many bytes are within this segment? */
if (nbytes > (XLogSegSize - startoff))
segbytes = XLogSegSize - startoff;
else
segbytes = nbytes;
readbytes = read(sendFile, buf, segbytes);
if (readbytes <= 0)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from log file %u, segment %u, offset %u, "
"length %lu: %m",
sendId, sendSeg, sendOff, (unsigned long) segbytes)));
/* Update state for read */
XLByteAdvance(recptr, readbytes);
sendOff += readbytes;
nbytes -= readbytes;
buf += readbytes;
}
/*
* 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.
*/
XLogGetLastRemoved(&lastRemovedLog, &lastRemovedSeg);
XLByteToSeg(startRecPtr, log, seg);
if (log < lastRemovedLog ||
(log == lastRemovedLog && seg <= lastRemovedSeg))
{
char filename[MAXFNAMELEN];
XLogFileName(filename, ThisTimeLineID, log, seg);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("requested WAL segment %s has already been removed",
filename)));
}
}
/*
* TODO: This is duplicate code with pg_xlogdump, similar to walsender.c, but
* we currently don't have the infrastructure (elog!) to share it.
*/
static void
XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
{
char *p;
XLogRecPtr recptr;
Size nbytes;
static int sendFile = -1;
static XLogSegNo sendSegNo = 0;
static uint32 sendOff = 0;
p = buf;
recptr = startptr;
nbytes = count;
while (nbytes > 0)
{
uint32 startoff;
int segbytes;
int readbytes;
startoff = recptr % XLogSegSize;
if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo))
{
char path[MAXPGPATH];
/* Switch to another logfile segment */
if (sendFile >= 0)
close(sendFile);
XLByteToSeg(recptr, sendSegNo);
XLogFilePath(path, tli, sendSegNo);
sendFile = BasicOpenFile(path, O_RDONLY | PG_BINARY, 0);
if (sendFile < 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)));
}
sendOff = 0;
}
/* Need to seek in the file? */
if (sendOff != startoff)
{
if (lseek(sendFile, (off_t) startoff, SEEK_SET) < 0)
{
char path[MAXPGPATH];
XLogFilePath(path, tli, sendSegNo);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not seek in log segment %s to offset %u: %m",
path, startoff)));
}
sendOff = startoff;
}
/* How many bytes are within this segment? */
if (nbytes > (XLogSegSize - startoff))
segbytes = XLogSegSize - startoff;
else
segbytes = nbytes;
readbytes = read(sendFile, p, segbytes);
if (readbytes <= 0)
{
char path[MAXPGPATH];
XLogFilePath(path, tli, sendSegNo);
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not read from log segment %s, offset %u, length %lu: %m",
path, sendOff, (unsigned long) segbytes)));
}
/* Update state for read */
recptr += readbytes;
sendOff += readbytes;
nbytes -= readbytes;
p += readbytes;
}
}
