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Commit30ba0d0

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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 parentf1d7516 commit30ba0d0

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5 files changed

+160
-1
lines changed

5 files changed

+160
-1
lines changed

‎src/backend/access/transam/xlog.c

Lines changed: 41 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -628,6 +628,7 @@ static bool read_backup_label(XLogRecPtr *checkPointLoc);
628628
staticvoidrm_redo_error_callback(void*arg);
629629
staticintget_sync_bit(intmethod);
630630

631+
staticvoidfsync_pgdata(char*datadir);
631632

632633
/*
633634
* Insert an XLOG record having the specified RMID and info bytes,
@@ -5924,6 +5925,18 @@ StartupXLOG(void)
59245925
(errmsg("database system was interrupted; last known up at %s",
59255926
str_time(ControlFile->time))));
59265927

5928+
/*
5929+
* If we previously crashed, there might be data which we had written,
5930+
* intending to fsync it, but which we had not actually fsync'd yet.
5931+
* Therefore, a power failure in the near future might cause earlier
5932+
* unflushed writes to be lost, even though more recent data written to
5933+
* disk from here on would be persisted. To avoid that, fsync the entire
5934+
* data directory.
5935+
*/
5936+
if (ControlFile->state!=DB_SHUTDOWNED&&
5937+
ControlFile->state!=DB_SHUTDOWNED_IN_RECOVERY)
5938+
fsync_pgdata(data_directory);
5939+
59275940
/* This is just to allow attaching to startup process with a debugger */
59285941
#ifdefXLOG_REPLAY_DELAY
59295942
if (ControlFile->state!=DB_SHUTDOWNED)
@@ -9967,3 +9980,31 @@ CheckForStandbyTrigger(void)
99679980
}
99689981
return false;
99699982
}
9983+
9984+
/*
9985+
* Issue fsync recursively on PGDATA and all its contents.
9986+
*/
9987+
staticvoid
9988+
fsync_pgdata(char*datadir)
9989+
{
9990+
if (!enableFsync)
9991+
return;
9992+
9993+
/*
9994+
* If possible, hint to the kernel that we're soon going to fsync
9995+
* the data directory and its contents.
9996+
*/
9997+
#if defined(HAVE_SYNC_FILE_RANGE)|| \
9998+
(defined(USE_POSIX_FADVISE)&& defined(POSIX_FADV_DONTNEED))
9999+
walkdir(datadir,pre_sync_fname);
10000+
#endif
10001+
10002+
/*
10003+
* Now we do the fsync()s in the same order.
10004+
*
10005+
* It's important to fsync the destination directory itself as individual
10006+
* file fsyncs don't guarantee that the directory entry for the file is
10007+
* synced.
10008+
*/
10009+
walkdir(datadir,fsync_fname);
10010+
}

‎src/backend/storage/file/fd.c

Lines changed: 115 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2004,3 +2004,118 @@ fsync_fname(char *fname, bool isdir)
20042004

20052005
close(fd);
20062006
}
2007+
2008+
/*
2009+
* Hint to the OS that it should get ready to fsync() this file.
2010+
*
2011+
* Adapted from pre_sync_fname in initdb.c
2012+
*/
2013+
void
2014+
pre_sync_fname(char*fname,boolisdir)
2015+
{
2016+
intfd;
2017+
2018+
fd=open(fname,O_RDONLY |PG_BINARY);
2019+
2020+
/*
2021+
* Some OSs don't allow us to open directories at all (Windows returns
2022+
* EACCES)
2023+
*/
2024+
if (fd<0&&isdir&& (errno==EISDIR||errno==EACCES))
2025+
return;
2026+
2027+
if (fd<0)
2028+
ereport(FATAL,
2029+
(errmsg("could not open file \"%s\" before fsync",
2030+
fname)));
2031+
2032+
pg_flush_data(fd,0,0);
2033+
2034+
close(fd);
2035+
}
2036+
2037+
/*
2038+
* walkdir: recursively walk a directory, applying the action to each
2039+
* regular file and directory (including the named directory itself)
2040+
* and following symbolic links.
2041+
*
2042+
* NB: There is another version of walkdir in initdb.c, but that version
2043+
* behaves differently with respect to symbolic links. Caveat emptor!
2044+
*/
2045+
void
2046+
walkdir(char*path,void (*action) (char*fname,boolisdir))
2047+
{
2048+
DIR*dir;
2049+
structdirent*de;
2050+
2051+
dir=AllocateDir(path);
2052+
while ((de=ReadDir(dir,path))!=NULL)
2053+
{
2054+
charsubpath[MAXPGPATH];
2055+
structstatfst;
2056+
2057+
CHECK_FOR_INTERRUPTS();
2058+
2059+
if (strcmp(de->d_name,".")==0||
2060+
strcmp(de->d_name,"..")==0)
2061+
continue;
2062+
2063+
snprintf(subpath,MAXPGPATH,"%s/%s",path,de->d_name);
2064+
2065+
if (lstat(subpath,&fst)<0)
2066+
ereport(ERROR,
2067+
(errcode_for_file_access(),
2068+
errmsg("could not stat file \"%s\": %m",subpath)));
2069+
2070+
if (S_ISREG(fst.st_mode))
2071+
(*action) (subpath, false);
2072+
elseif (S_ISDIR(fst.st_mode))
2073+
walkdir(subpath,action);
2074+
#ifndefWIN32
2075+
elseif (S_ISLNK(fst.st_mode))
2076+
#else
2077+
elseif (pg_win32_is_junction(subpath))
2078+
#endif
2079+
{
2080+
#if defined(HAVE_READLINK)|| defined(WIN32)
2081+
charlinkpath[MAXPGPATH];
2082+
intlen;
2083+
structstatlst;
2084+
2085+
len=readlink(subpath,linkpath,sizeof(linkpath)-1);
2086+
if (len<0)
2087+
ereport(ERROR,
2088+
(errcode_for_file_access(),
2089+
errmsg("could not read symbolic link \"%s\": %m",
2090+
subpath)));
2091+
2092+
if (len >=sizeof(linkpath)-1)
2093+
ereport(ERROR,
2094+
(errmsg("symbolic link \"%s\" target is too long",
2095+
subpath)));
2096+
2097+
linkpath[len]='\0';
2098+
2099+
if (lstat(linkpath,&lst)==0)
2100+
{
2101+
if (S_ISREG(lst.st_mode))
2102+
(*action) (linkpath, false);
2103+
elseif (S_ISDIR(lst.st_mode))
2104+
walkdir(subpath,action);
2105+
}
2106+
elseif (errno!=ENOENT)
2107+
ereport(ERROR,
2108+
(errcode_for_file_access(),
2109+
errmsg("could not stat file \"%s\": %m",linkpath)));
2110+
#else
2111+
ereport(WARNING,
2112+
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
2113+
errmsg("this platform does not support symbolic links; ignoring \"%s\"",
2114+
subpath)));
2115+
#endif
2116+
}
2117+
}
2118+
FreeDir(dir);
2119+
2120+
(*action) (path, true);
2121+
}

‎src/backend/utils/misc/guc.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -377,6 +377,7 @@ inttrace_recovery_messages = LOG;
377377

378378
intnum_temp_buffers=1000;
379379

380+
char*data_directory;
380381
char*ConfigFileName;
381382
char*HbaFileName;
382383
char*IdentFileName;
@@ -414,7 +415,6 @@ static char *timezone_string;
414415
staticchar*log_timezone_string;
415416
staticchar*timezone_abbreviations_string;
416417
staticchar*XactIsoLevel_string;
417-
staticchar*data_directory;
418418
staticchar*custom_variable_classes;
419419
staticintmax_function_args;
420420
staticintmax_index_keys;

‎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"

‎src/include/utils/guc.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -176,6 +176,7 @@ extern intlog_temp_files;
176176

177177
externintnum_temp_buffers;
178178

179+
externchar*data_directory;
179180
externchar*ConfigFileName;
180181
externchar*HbaFileName;
181182
externchar*IdentFileName;

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