postgrespro.git / summary / log / commit / refs

commit    7bb3102cea02101efcbb4c4fba3fdd452a52bdab
Author:   Thomas Munro <tmunro@postgresql.org>
Date:     Sat Dec 14 02:54:31 2019 +0000

    Don't use _mdfd_getseg() in mdsyncfiletag().
    
    _mdfd_getseg() opens all segments up to the requested one.  That
    causes problems for mdsyncfiletag(), if mdunlinkfork() has
    already unlinked other segment files.  Open the file we want
    directly by name instead, if it's not already open.
    
    The consequence of this bug was a rare panic in the checkpointer,
    made more likely if you saturated the sync request queue so that
    the SYNC_FORGET_REQUEST messages for a given relation were more
    likely to be absorbed in separate cycles by the checkpointer.
    
    Back-patch to 12.  Defect in commit 3eb77eba.
    
    Author: Thomas Munro
    Reported-by: Justin Pryzby
    Discussion: https://postgr.es/m/20191119115759.GI30362%40telsasoft.com


 src/backend/storage/smgr/md.c | 57 ++++++++++++++++++++++++++++++-------------
 1 file changed, 40 insertions(+), 17 deletions(-)

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 8a9eaf6430..b110518a86 100644
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -1280,25 +1280,48 @@ int
 mdsyncfiletag(const FileTag *ftag, char *path)
 {
 	SMgrRelation reln = smgropen(ftag->rnode, InvalidBackendId);
-	MdfdVec    *v;
-	char	   *p;
+	int			fd,
+				result,
+				save_errno;
+	bool		need_to_close;
 
-	/* Provide the path for informational messages. */
-	p = _mdfd_segpath(reln, ftag->forknum, ftag->segno);
-	strlcpy(path, p, MAXPGPATH);
-	pfree(p);
+	/* See if we already have the file open, or need to open it. */
+	if (ftag->segno < reln->md_num_open_segs[ftag->forknum])
+	{
+		File		file;
+
+		file = reln->md_seg_fds[ftag->forknum][ftag->segno].mdfd_vfd;
+		strlcpy(path, FilePathName(file), MAXPGPATH);
+		fd = FileGetRawDesc(file);
+		need_to_close = false;
+	}
+	else
+	{
+		char	   *p;
+
+		p = _mdfd_segpath(reln, ftag->forknum, ftag->segno);
+		strlcpy(path, p, MAXPGPATH);
+		pfree(p);
+
+		fd = OpenTransientFile(path, O_RDWR);
+		if (fd < 0)
+			return -1;
+		need_to_close = true;
+	}
+
+	/* Sync the file. */
+	pgstat_report_wait_start(WAIT_EVENT_DATA_FILE_SYNC);
+	result = pg_fsync(fd);
+	save_errno = errno;
+	pgstat_report_wait_end();
+
+	if (need_to_close && CloseTransientFile(fd) != 0)
+		ereport(WARNING,
+				(errcode_for_file_access(),
+				 errmsg("could not close file \"%s\": %m", path)));
+	errno = save_errno;
 
-	/* Try to open the requested segment. */
-	v = _mdfd_getseg(reln,
-					 ftag->forknum,
-					 ftag->segno * (BlockNumber) RELSEG_SIZE,
-					 false,
-					 EXTENSION_RETURN_NULL | EXTENSION_DONT_CHECK_SIZE);
-	if (v == NULL)
-		return -1;
-
-	/* Try to fsync the file. */
-	return FileSync(v->mdfd_vfd, WAIT_EVENT_DATA_FILE_SYNC);
+	return result;
 }
 
 /*


[parent: a7ee7c851322]