Retry short writes when flushing WAL.
We don't normally bother retrying when the number of bytes written by write() is short of what was requested. It is generally assumed that a write() to disk doesn't return short, unless you run out of disk space. While writing the WAL, however, it seems prudent to try a bit harder, because a failure leads to PANIC. The write() is also much larger than most write()s in the backend (up to wal_buffers), so there's more room for surprises. Also retry on EINTR. All signals used in the backend are flagged SA_RESTART nowadays, so it shouldn't happen, but better to be defensive.
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@ -1606,6 +1606,8 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
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{
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char *from;
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Size nbytes;
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Size nleft;
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int written;
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/* Need to seek in the file? */
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if (openLogOff != startoffset)
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@ -1622,19 +1624,25 @@ XLogWrite(XLogwrtRqst WriteRqst, bool flexible, bool xlog_switch)
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/* OK to write the page(s) */
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from = XLogCtl->pages + startidx * (Size) XLOG_BLCKSZ;
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nbytes = npages * (Size) XLOG_BLCKSZ;
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errno = 0;
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if (write(openLogFile, from, nbytes) != nbytes)
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nleft = nbytes;
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do
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{
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/* if write didn't set errno, assume no disk space */
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if (errno == 0)
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errno = ENOSPC;
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not write to log file %s "
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"at offset %u, length %lu: %m",
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XLogFileNameP(ThisTimeLineID, openLogSegNo),
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openLogOff, (unsigned long) nbytes)));
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}
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errno = 0;
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written = write(openLogFile, from, nleft);
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if (written <= 0)
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{
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if (errno == EINTR)
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continue;
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ereport(PANIC,
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(errcode_for_file_access(),
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errmsg("could not write to log file %s "
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"at offset %u, length %lu: %m",
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XLogFileNameP(ThisTimeLineID, openLogSegNo),
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openLogOff, (unsigned long) nbytes)));
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}
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nleft -= written;
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from += written;
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} while (nleft > 0);
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/* Update state for write */
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openLogOff += nbytes;
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