diff options
| -rw-r--r-- | src/backend/backup/basebackup.c | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/src/backend/backup/basebackup.c b/src/backend/backup/basebackup.c index 6547e37d125..6efdefb5917 100644 --- a/src/backend/backup/basebackup.c +++ b/src/backend/backup/basebackup.c @@ -1602,11 +1602,21 @@ sendFile(bbsink *sink, const char *readfilename, const char *tarfilename, * Retry the block on the first failure. It's * possible that we read the first 4K page of the * block just before postgres updated the entire block - * so it ends up looking torn to us. We only need to - * retry once because the LSN should be updated to - * something we can ignore on the next pass. If the - * error happens again then it is a true validation - * failure. + * so it ends up looking torn to us. If, before we + * retry the read, the concurrent write of the block + * finishes, the page LSN will be updated and we'll + * realize that we should ignore this block. + * + * There's no guarantee that this will actually + * happen, though: the torn write could take an + * arbitrarily long time to complete. Retrying multiple + * times wouldn't fix this problem, either, though + * it would reduce the chances of it happening in + * practice. The only real fix here seems to be to + * have some kind of interlock that allows us to wait + * until we can be certain that no write to the block + * is in progress. Since we don't have any such thing + * right now, we just do this and hope for the best. */ if (block_retry == false) { |