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Commit2bc3397

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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 parent7c2ccb4 commit2bc3397

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3 files changed

+158
-0
lines changed

3 files changed

+158
-0
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 41 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -701,6 +701,7 @@ static bool read_backup_label(XLogRecPtr *checkPointLoc,
701701
staticvoidrm_redo_error_callback(void*arg);
702702
staticintget_sync_bit(intmethod);
703703

704+
staticvoidfsync_pgdata(char*datadir);
704705

705706
/*
706707
* Insert an XLOG record having the specified RMID and info bytes,
@@ -6417,6 +6418,18 @@ StartupXLOG(void)
64176418
(errmsg("database system was interrupted; last known up at %s",
64186419
str_time(ControlFile->time))));
64196420

6421+
/*
6422+
* If we previously crashed, there might be data which we had written,
6423+
* intending to fsync it, but which we had not actually fsync'd yet.
6424+
* Therefore, a power failure in the near future might cause earlier
6425+
* unflushed writes to be lost, even though more recent data written to
6426+
* disk from here on would be persisted. To avoid that, fsync the entire
6427+
* data directory.
6428+
*/
6429+
if (ControlFile->state!=DB_SHUTDOWNED&&
6430+
ControlFile->state!=DB_SHUTDOWNED_IN_RECOVERY)
6431+
fsync_pgdata(data_directory);
6432+
64206433
/* This is just to allow attaching to startup process with a debugger */
64216434
#ifdefXLOG_REPLAY_DELAY
64226435
if (ControlFile->state!=DB_SHUTDOWNED)
@@ -11014,3 +11027,31 @@ SetWalWriterSleeping(bool sleeping)
1101411027
xlogctl->WalWriterSleeping=sleeping;
1101511028
SpinLockRelease(&xlogctl->info_lck);
1101611029
}
11030+
11031+
/*
11032+
* Issue fsync recursively on PGDATA and all its contents.
11033+
*/
11034+
staticvoid
11035+
fsync_pgdata(char*datadir)
11036+
{
11037+
if (!enableFsync)
11038+
return;
11039+
11040+
/*
11041+
* If possible, hint to the kernel that we're soon going to fsync
11042+
* the data directory and its contents.
11043+
*/
11044+
#if defined(HAVE_SYNC_FILE_RANGE)|| \
11045+
(defined(USE_POSIX_FADVISE)&& defined(POSIX_FADV_DONTNEED))
11046+
walkdir(datadir,pre_sync_fname);
11047+
#endif
11048+
11049+
/*
11050+
* Now we do the fsync()s in the same order.
11051+
*
11052+
* It's important to fsync the destination directory itself as individual
11053+
* file fsyncs don't guarantee that the directory entry for the file is
11054+
* synced.
11055+
*/
11056+
walkdir(datadir,fsync_fname);
11057+
}

‎src/backend/storage/file/fd.c

Lines changed: 115 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2265,3 +2265,118 @@ looks_like_temp_rel_name(const char *name)
22652265
return false;
22662266
return true;
22672267
}
2268+
2269+
/*
2270+
* Hint to the OS that it should get ready to fsync() this file.
2271+
*
2272+
* Adapted from pre_sync_fname in initdb.c
2273+
*/
2274+
void
2275+
pre_sync_fname(char*fname,boolisdir)
2276+
{
2277+
intfd;
2278+
2279+
fd=open(fname,O_RDONLY |PG_BINARY);
2280+
2281+
/*
2282+
* Some OSs don't allow us to open directories at all (Windows returns
2283+
* EACCES)
2284+
*/
2285+
if (fd<0&&isdir&& (errno==EISDIR||errno==EACCES))
2286+
return;
2287+
2288+
if (fd<0)
2289+
ereport(FATAL,
2290+
(errmsg("could not open file \"%s\" before fsync",
2291+
fname)));
2292+
2293+
pg_flush_data(fd,0,0);
2294+
2295+
close(fd);
2296+
}
2297+
2298+
/*
2299+
* walkdir: recursively walk a directory, applying the action to each
2300+
* regular file and directory (including the named directory itself)
2301+
* and following symbolic links.
2302+
*
2303+
* NB: There is another version of walkdir in initdb.c, but that version
2304+
* behaves differently with respect to symbolic links. Caveat emptor!
2305+
*/
2306+
void
2307+
walkdir(char*path,void (*action) (char*fname,boolisdir))
2308+
{
2309+
DIR*dir;
2310+
structdirent*de;
2311+
2312+
dir=AllocateDir(path);
2313+
while ((de=ReadDir(dir,path))!=NULL)
2314+
{
2315+
charsubpath[MAXPGPATH];
2316+
structstatfst;
2317+
2318+
CHECK_FOR_INTERRUPTS();
2319+
2320+
if (strcmp(de->d_name,".")==0||
2321+
strcmp(de->d_name,"..")==0)
2322+
continue;
2323+
2324+
snprintf(subpath,MAXPGPATH,"%s/%s",path,de->d_name);
2325+
2326+
if (lstat(subpath,&fst)<0)
2327+
ereport(ERROR,
2328+
(errcode_for_file_access(),
2329+
errmsg("could not stat file \"%s\": %m",subpath)));
2330+
2331+
if (S_ISREG(fst.st_mode))
2332+
(*action) (subpath, false);
2333+
elseif (S_ISDIR(fst.st_mode))
2334+
walkdir(subpath,action);
2335+
#ifndefWIN32
2336+
elseif (S_ISLNK(fst.st_mode))
2337+
#else
2338+
elseif (pg_win32_is_junction(subpath))
2339+
#endif
2340+
{
2341+
#if defined(HAVE_READLINK)|| defined(WIN32)
2342+
charlinkpath[MAXPGPATH];
2343+
intlen;
2344+
structstatlst;
2345+
2346+
len=readlink(subpath,linkpath,sizeof(linkpath)-1);
2347+
if (len<0)
2348+
ereport(ERROR,
2349+
(errcode_for_file_access(),
2350+
errmsg("could not read symbolic link \"%s\": %m",
2351+
subpath)));
2352+
2353+
if (len >=sizeof(linkpath)-1)
2354+
ereport(ERROR,
2355+
(errmsg("symbolic link \"%s\" target is too long",
2356+
subpath)));
2357+
2358+
linkpath[len]='\0';
2359+
2360+
if (lstat(linkpath,&lst)==0)
2361+
{
2362+
if (S_ISREG(lst.st_mode))
2363+
(*action) (linkpath, false);
2364+
elseif (S_ISDIR(lst.st_mode))
2365+
walkdir(subpath,action);
2366+
}
2367+
elseif (errno!=ENOENT)
2368+
ereport(ERROR,
2369+
(errcode_for_file_access(),
2370+
errmsg("could not stat file \"%s\": %m",linkpath)));
2371+
#else
2372+
ereport(WARNING,
2373+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2374+
errmsg("this platform does not support symbolic links; ignoring \"%s\"",
2375+
subpath)));
2376+
#endif
2377+
}
2378+
}
2379+
FreeDir(dir);
2380+
2381+
(*action) (path, true);
2382+
}

‎src/include/storage/fd.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -105,6 +105,8 @@ extern intpg_fsync_writethrough(int fd);
105105
externintpg_fdatasync(intfd);
106106
externintpg_flush_data(intfd,off_toffset,off_tamount);
107107
externvoidfsync_fname(char*fname,boolisdir);
108+
externvoidpre_sync_fname(char*fname,boolisdir);
109+
externvoidwalkdir(char*path,void (*action) (char*fname,boolisdir));
108110

109111
/* Filename components for OpenTemporaryFile */
110112
#definePG_TEMP_FILES_DIR "pgsql_tmp"

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