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Commit4b71d28

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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 parent1dadd36 commit4b71d28

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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
@@ -678,6 +678,7 @@ static bool read_backup_label(XLogRecPtr *checkPointLoc,
678678
staticvoidrm_redo_error_callback(void*arg);
679679
staticintget_sync_bit(intmethod);
680680

681+
staticvoidfsync_pgdata(char*datadir);
681682

682683
/*
683684
* Insert an XLOG record having the specified RMID and info bytes,
@@ -6229,6 +6230,18 @@ StartupXLOG(void)
62296230
(errmsg("database system was interrupted; last known up at %s",
62306231
str_time(ControlFile->time))));
62316232

6233+
/*
6234+
* If we previously crashed, there might be data which we had written,
6235+
* intending to fsync it, but which we had not actually fsync'd yet.
6236+
* Therefore, a power failure in the near future might cause earlier
6237+
* unflushed writes to be lost, even though more recent data written to
6238+
* disk from here on would be persisted. To avoid that, fsync the entire
6239+
* data directory.
6240+
*/
6241+
if (ControlFile->state!=DB_SHUTDOWNED&&
6242+
ControlFile->state!=DB_SHUTDOWNED_IN_RECOVERY)
6243+
fsync_pgdata(data_directory);
6244+
62326245
/* This is just to allow attaching to startup process with a debugger */
62336246
#ifdefXLOG_REPLAY_DELAY
62346247
if (ControlFile->state!=DB_SHUTDOWNED)
@@ -10825,3 +10838,31 @@ WakeupRecovery(void)
1082510838
{
1082610839
SetLatch(&XLogCtl->recoveryWakeupLatch);
1082710840
}
10841+
10842+
/*
10843+
* Issue fsync recursively on PGDATA and all its contents.
10844+
*/
10845+
staticvoid
10846+
fsync_pgdata(char*datadir)
10847+
{
10848+
if (!enableFsync)
10849+
return;
10850+
10851+
/*
10852+
* If possible, hint to the kernel that we're soon going to fsync
10853+
* the data directory and its contents.
10854+
*/
10855+
#if defined(HAVE_SYNC_FILE_RANGE)|| \
10856+
(defined(USE_POSIX_FADVISE)&& defined(POSIX_FADV_DONTNEED))
10857+
walkdir(datadir,pre_sync_fname);
10858+
#endif
10859+
10860+
/*
10861+
* Now we do the fsync()s in the same order.
10862+
*
10863+
* It's important to fsync the destination directory itself as individual
10864+
* file fsyncs don't guarantee that the directory entry for the file is
10865+
* synced.
10866+
*/
10867+
walkdir(datadir,fsync_fname);
10868+
}

‎src/backend/storage/file/fd.c

Lines changed: 115 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2206,3 +2206,118 @@ looks_like_temp_rel_name(const char *name)
22062206
return false;
22072207
return true;
22082208
}
2209+
2210+
/*
2211+
* Hint to the OS that it should get ready to fsync() this file.
2212+
*
2213+
* Adapted from pre_sync_fname in initdb.c
2214+
*/
2215+
void
2216+
pre_sync_fname(char*fname,boolisdir)
2217+
{
2218+
intfd;
2219+
2220+
fd=open(fname,O_RDONLY |PG_BINARY);
2221+
2222+
/*
2223+
* Some OSs don't allow us to open directories at all (Windows returns
2224+
* EACCES)
2225+
*/
2226+
if (fd<0&&isdir&& (errno==EISDIR||errno==EACCES))
2227+
return;
2228+
2229+
if (fd<0)
2230+
ereport(FATAL,
2231+
(errmsg("could not open file \"%s\" before fsync",
2232+
fname)));
2233+
2234+
pg_flush_data(fd,0,0);
2235+
2236+
close(fd);
2237+
}
2238+
2239+
/*
2240+
* walkdir: recursively walk a directory, applying the action to each
2241+
* regular file and directory (including the named directory itself)
2242+
* and following symbolic links.
2243+
*
2244+
* NB: There is another version of walkdir in initdb.c, but that version
2245+
* behaves differently with respect to symbolic links. Caveat emptor!
2246+
*/
2247+
void
2248+
walkdir(char*path,void (*action) (char*fname,boolisdir))
2249+
{
2250+
DIR*dir;
2251+
structdirent*de;
2252+
2253+
dir=AllocateDir(path);
2254+
while ((de=ReadDir(dir,path))!=NULL)
2255+
{
2256+
charsubpath[MAXPGPATH];
2257+
structstatfst;
2258+
2259+
CHECK_FOR_INTERRUPTS();
2260+
2261+
if (strcmp(de->d_name,".")==0||
2262+
strcmp(de->d_name,"..")==0)
2263+
continue;
2264+
2265+
snprintf(subpath,MAXPGPATH,"%s/%s",path,de->d_name);
2266+
2267+
if (lstat(subpath,&fst)<0)
2268+
ereport(ERROR,
2269+
(errcode_for_file_access(),
2270+
errmsg("could not stat file \"%s\": %m",subpath)));
2271+
2272+
if (S_ISREG(fst.st_mode))
2273+
(*action) (subpath, false);
2274+
elseif (S_ISDIR(fst.st_mode))
2275+
walkdir(subpath,action);
2276+
#ifndefWIN32
2277+
elseif (S_ISLNK(fst.st_mode))
2278+
#else
2279+
elseif (pg_win32_is_junction(subpath))
2280+
#endif
2281+
{
2282+
#if defined(HAVE_READLINK)|| defined(WIN32)
2283+
charlinkpath[MAXPGPATH];
2284+
intlen;
2285+
structstatlst;
2286+
2287+
len=readlink(subpath,linkpath,sizeof(linkpath)-1);
2288+
if (len<0)
2289+
ereport(ERROR,
2290+
(errcode_for_file_access(),
2291+
errmsg("could not read symbolic link \"%s\": %m",
2292+
subpath)));
2293+
2294+
if (len >=sizeof(linkpath)-1)
2295+
ereport(ERROR,
2296+
(errmsg("symbolic link \"%s\" target is too long",
2297+
subpath)));
2298+
2299+
linkpath[len]='\0';
2300+
2301+
if (lstat(linkpath,&lst)==0)
2302+
{
2303+
if (S_ISREG(lst.st_mode))
2304+
(*action) (linkpath, false);
2305+
elseif (S_ISDIR(lst.st_mode))
2306+
walkdir(subpath,action);
2307+
}
2308+
elseif (errno!=ENOENT)
2309+
ereport(ERROR,
2310+
(errcode_for_file_access(),
2311+
errmsg("could not stat file \"%s\": %m",linkpath)));
2312+
#else
2313+
ereport(WARNING,
2314+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2315+
errmsg("this platform does not support symbolic links; ignoring \"%s\"",
2316+
subpath)));
2317+
#endif
2318+
}
2319+
}
2320+
FreeDir(dir);
2321+
2322+
(*action) (path, true);
2323+
}

‎src/include/storage/fd.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -100,6 +100,8 @@ extern intpg_fsync_writethrough(int fd);
100100
externintpg_fdatasync(intfd);
101101
externintpg_flush_data(intfd,off_toffset,off_tamount);
102102
externvoidfsync_fname(char*fname,boolisdir);
103+
externvoidpre_sync_fname(char*fname,boolisdir);
104+
externvoidwalkdir(char*path,void (*action) (char*fname,boolisdir));
103105

104106
/* Filename components for OpenTemporaryFile */
105107
#definePG_TEMP_FILES_DIR "pgsql_tmp"

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