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Fix fsync-at-startup code to not treat errors as fatal.

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Commit 2ce439f337 introduced a rather serious
regression, namely that if its scan of the data directory came across any
un-fsync-able files, it would fail and thereby prevent database startup.
Worse yet, symlinks to such files also caused the problem, which meant that
crash restart was guaranteed to fail on certain common installations such
as older Debian.

After discussion, we agreed that (1) failure to start is worse than any
consequence of not fsync'ing is likely to be, therefore treat all errors
in this code as nonfatal; (2) we should not chase symlinks other than
those that are expected to exist, namely pg_xlog/ and tablespace links
under pg_tblspc/.  The latter restriction avoids possibly fsync'ing a
much larger part of the filesystem than intended, if the user has left
random symlinks hanging about in the data directory.

This commit takes care of that and also does some code beautification,
mainly moving the relevant code into fd.c, which seems a much better place
for it than xlog.c, and making sure that the conditional compilation for
the pre_sync_fname pass has something to do with whether pg_flush_data
works.

I also relocated the call site in xlog.c down a few lines; it seems a
bit silly to be doing this before ValidateXLOGDirectoryStructure().

The similar logic in initdb.c ought to be made to match this, but that
change is noncritical and will be dealt with separately.

Back-patch to all active branches, like the prior commit.

Abhijit Menon-Sen and Tom Lane
This commit is contained in:
Tom Lane
2015-05-28 17:33:03 -04:00
parent d5442cb243
commit d8179b001a
3 changed files with 262 additions and 118 deletions
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3
src/include/storage/fd.h
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@@ -114,8 +114,7 @@ extern int pg_fsync_writethrough(int fd);
extern int pg_fdatasync(int fd);
extern int pg_flush_data(int fd, off_t offset, off_t amount);
extern void fsync_fname(char *fname, bool isdir);
extern void pre_sync_fname(char *fname, bool isdir);
extern void walkdir(char *path, void (*action) (char *fname, bool isdir));
extern void SyncDataDirectory(void);
/* Filename components for OpenTemporaryFile */
#define PG_TEMP_FILES_DIR "pgsql_tmp"