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Commit2ce439f

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Recursively fsync() the data directory after a crash.
Otherwise, if there's another crash, some writes from after the firstcrash might make it to disk while writes from before the crash failto make it to disk. This could lead to data corruption.Back-patch to all supported versions.Abhijit Menon-Sen, reviewed by Andres Freund and slightly revisedby me.
1 parentec3d976 commit2ce439f

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3 files changed

+159
-0
lines changed

3 files changed

+159
-0
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 42 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -845,6 +845,8 @@ static void WALInsertLockAcquireExclusive(void);
845845
staticvoidWALInsertLockRelease(void);
846846
staticvoidWALInsertLockUpdateInsertingAt(XLogRecPtrinsertingAt);
847847

848+
staticvoidfsync_pgdata(char*datadir);
849+
848850
/*
849851
* Insert an XLOG record represented by an already-constructed chain of data
850852
* chunks. This is a low-level routine; to construct the WAL record header
@@ -5910,6 +5912,18 @@ StartupXLOG(void)
59105912
(errmsg("database system was interrupted; last known up at %s",
59115913
str_time(ControlFile->time))));
59125914

5915+
/*
5916+
* If we previously crashed, there might be data which we had written,
5917+
* intending to fsync it, but which we had not actually fsync'd yet.
5918+
* Therefore, a power failure in the near future might cause earlier
5919+
* unflushed writes to be lost, even though more recent data written to
5920+
* disk from here on would be persisted. To avoid that, fsync the entire
5921+
* data directory.
5922+
*/
5923+
if (ControlFile->state!=DB_SHUTDOWNED&&
5924+
ControlFile->state!=DB_SHUTDOWNED_IN_RECOVERY)
5925+
fsync_pgdata(data_directory);
5926+
59135927
/* This is just to allow attaching to startup process with a debugger */
59145928
#ifdefXLOG_REPLAY_DELAY
59155929
if (ControlFile->state!=DB_SHUTDOWNED)
@@ -11123,3 +11137,31 @@ SetWalWriterSleeping(bool sleeping)
1112311137
XLogCtl->WalWriterSleeping=sleeping;
1112411138
SpinLockRelease(&XLogCtl->info_lck);
1112511139
}
11140+
11141+
/*
11142+
* Issue fsync recursively on PGDATA and all its contents.
11143+
*/
11144+
staticvoid
11145+
fsync_pgdata(char*datadir)
11146+
{
11147+
if (!enableFsync)
11148+
return;
11149+
11150+
/*
11151+
* If possible, hint to the kernel that we're soon going to fsync
11152+
* the data directory and its contents.
11153+
*/
11154+
#if defined(HAVE_SYNC_FILE_RANGE)|| \
11155+
(defined(USE_POSIX_FADVISE)&& defined(POSIX_FADV_DONTNEED))
11156+
walkdir(datadir,pre_sync_fname);
11157+
#endif
11158+
11159+
/*
11160+
* Now we do the fsync()s in the same order.
11161+
*
11162+
* It's important to fsync the destination directory itself as individual
11163+
* file fsyncs don't guarantee that the directory entry for the file is
11164+
* synced.
11165+
*/
11166+
walkdir(datadir,fsync_fname);
11167+
}

‎src/backend/storage/file/fd.c

Lines changed: 115 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2439,3 +2439,118 @@ looks_like_temp_rel_name(const char *name)
24392439
return false;
24402440
return true;
24412441
}
2442+
2443+
/*
2444+
* Hint to the OS that it should get ready to fsync() this file.
2445+
*
2446+
* Adapted from pre_sync_fname in initdb.c
2447+
*/
2448+
void
2449+
pre_sync_fname(char*fname,boolisdir)
2450+
{
2451+
intfd;
2452+
2453+
fd=open(fname,O_RDONLY |PG_BINARY);
2454+
2455+
/*
2456+
* Some OSs don't allow us to open directories at all (Windows returns
2457+
* EACCES)
2458+
*/
2459+
if (fd<0&&isdir&& (errno==EISDIR||errno==EACCES))
2460+
return;
2461+
2462+
if (fd<0)
2463+
ereport(FATAL,
2464+
(errmsg("could not open file \"%s\" before fsync",
2465+
fname)));
2466+
2467+
pg_flush_data(fd,0,0);
2468+
2469+
close(fd);
2470+
}
2471+
2472+
/*
2473+
* walkdir: recursively walk a directory, applying the action to each
2474+
* regular file and directory (including the named directory itself)
2475+
* and following symbolic links.
2476+
*
2477+
* NB: There is another version of walkdir in initdb.c, but that version
2478+
* behaves differently with respect to symbolic links. Caveat emptor!
2479+
*/
2480+
void
2481+
walkdir(char*path,void (*action) (char*fname,boolisdir))
2482+
{
2483+
DIR*dir;
2484+
structdirent*de;
2485+
2486+
dir=AllocateDir(path);
2487+
while ((de=ReadDir(dir,path))!=NULL)
2488+
{
2489+
charsubpath[MAXPGPATH];
2490+
structstatfst;
2491+
2492+
CHECK_FOR_INTERRUPTS();
2493+
2494+
if (strcmp(de->d_name,".")==0||
2495+
strcmp(de->d_name,"..")==0)
2496+
continue;
2497+
2498+
snprintf(subpath,MAXPGPATH,"%s/%s",path,de->d_name);
2499+
2500+
if (lstat(subpath,&fst)<0)
2501+
ereport(ERROR,
2502+
(errcode_for_file_access(),
2503+
errmsg("could not stat file \"%s\": %m",subpath)));
2504+
2505+
if (S_ISREG(fst.st_mode))
2506+
(*action) (subpath, false);
2507+
elseif (S_ISDIR(fst.st_mode))
2508+
walkdir(subpath,action);
2509+
#ifndefWIN32
2510+
elseif (S_ISLNK(fst.st_mode))
2511+
#else
2512+
elseif (pg_win32_is_junction(subpath))
2513+
#endif
2514+
{
2515+
#if defined(HAVE_READLINK)|| defined(WIN32)
2516+
charlinkpath[MAXPGPATH];
2517+
intlen;
2518+
structstatlst;
2519+
2520+
len=readlink(subpath,linkpath,sizeof(linkpath)-1);
2521+
if (len<0)
2522+
ereport(ERROR,
2523+
(errcode_for_file_access(),
2524+
errmsg("could not read symbolic link \"%s\": %m",
2525+
subpath)));
2526+
2527+
if (len >=sizeof(linkpath)-1)
2528+
ereport(ERROR,
2529+
(errmsg("symbolic link \"%s\" target is too long",
2530+
subpath)));
2531+
2532+
linkpath[len]='\0';
2533+
2534+
if (lstat(linkpath,&lst)==0)
2535+
{
2536+
if (S_ISREG(lst.st_mode))
2537+
(*action) (linkpath, false);
2538+
elseif (S_ISDIR(lst.st_mode))
2539+
walkdir(subpath,action);
2540+
}
2541+
elseif (errno!=ENOENT)
2542+
ereport(ERROR,
2543+
(errcode_for_file_access(),
2544+
errmsg("could not stat file \"%s\": %m",linkpath)));
2545+
#else
2546+
ereport(WARNING,
2547+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2548+
errmsg("this platform does not support symbolic links; ignoring \"%s\"",
2549+
subpath)));
2550+
#endif
2551+
}
2552+
}
2553+
FreeDir(dir);
2554+
2555+
(*action) (path, true);
2556+
}

‎src/include/storage/fd.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -114,6 +114,8 @@ extern intpg_fsync_writethrough(int fd);
114114
externintpg_fdatasync(intfd);
115115
externintpg_flush_data(intfd,off_toffset,off_tamount);
116116
externvoidfsync_fname(char*fname,boolisdir);
117+
externvoidpre_sync_fname(char*fname,boolisdir);
118+
externvoidwalkdir(char*path,void (*action) (char*fname,boolisdir));
117119

118120
/* Filename components for OpenTemporaryFile */
119121
#definePG_TEMP_FILES_DIR "pgsql_tmp"

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