Recursively fsync() the data directory after a crash.

Otherwise, if there's another crash, some writes from after the first
crash might make it to disk while writes from before the crash fail
to 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 revised
by me.

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 7bba264b5d69b89823b3ca12fa38b9cca3fc2bfd..2ef9a94cc09171e96abd9c7fae51c48d8b741f10 100644 (file)
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -826,6 +826,8 @@ static void WALInsertLockAcquireExclusive(void);
 static void WALInsertLockRelease(void);
 static void WALInsertLockUpdateInsertingAt(XLogRecPtr insertingAt);
 
+static void fsync_pgdata(char *datadir);
+
 /*
  * Insert an XLOG record having the specified RMID and info bytes,
  * with the body of the record being the data chunk(s) described by
@@ -6116,6 +6118,18 @@ StartupXLOG(void)
                          (errmsg("database system was interrupted; last known up at %s",
                                          str_time(ControlFile->time))));
 
+       /*
+        * If we previously crashed, there might be data which we had written,
+        * intending to fsync it, but which we had not actually fsync'd yet.
+        * Therefore, a power failure in the near future might cause earlier
+        * unflushed writes to be lost, even though more recent data written to
+        * disk from here on would be persisted.  To avoid that, fsync the entire
+        * data directory.
+        */
+       if (ControlFile->state != DB_SHUTDOWNED &&
+               ControlFile->state != DB_SHUTDOWNED_IN_RECOVERY)
+               fsync_pgdata(data_directory);
+
        /* This is just to allow attaching to startup process with a debugger */
 #ifdef XLOG_REPLAY_DELAY
        if (ControlFile->state != DB_SHUTDOWNED)
@@ -11338,3 +11352,31 @@ SetWalWriterSleeping(bool sleeping)
        xlogctl->WalWriterSleeping = sleeping;
        SpinLockRelease(&xlogctl->info_lck);
 }
+
+/*
+ * Issue fsync recursively on PGDATA and all its contents.
+ */
+static void
+fsync_pgdata(char *datadir)
+{
+       if (!enableFsync)
+               return;
+
+       /*
+        * If possible, hint to the kernel that we're soon going to fsync
+        * the data directory and its contents.
+        */
+#if defined(HAVE_SYNC_FILE_RANGE) || \
+       (defined(USE_POSIX_FADVISE) && defined(POSIX_FADV_DONTNEED))
+       walkdir(datadir, pre_sync_fname);
+#endif
+
+       /*
+        * Now we do the fsync()s in the same order.
+        *
+        * It's important to fsync the destination directory itself as individual
+        * file fsyncs don't guarantee that the directory entry for the file is
+        * synced.
+        */
+       walkdir(datadir, fsync_fname);
+}

diff --git a/src/backend/storage/file/fd.c b/src/backend/storage/file/fd.c
index 1f69c9e03c918130abc63fa9daa903d998bc29c1..f34e618ac5a8cb94d3d094e5d96781555bd12173 100644 (file)
--- a/src/backend/storage/file/fd.c
+++ b/src/backend/storage/file/fd.c
@@ -2438,3 +2438,118 @@ looks_like_temp_rel_name(const char *name)
                return false;
        return true;
 }
+
+/*
+ * Hint to the OS that it should get ready to fsync() this file.
+ *
+ * Adapted from pre_sync_fname in initdb.c
+ */
+void
+pre_sync_fname(char *fname, bool isdir)
+{
+       int                     fd;
+
+       fd = open(fname, O_RDONLY | PG_BINARY);
+
+       /*
+        * Some OSs don't allow us to open directories at all (Windows returns
+        * EACCES)
+        */
+       if (fd < 0 && isdir && (errno == EISDIR || errno == EACCES))
+               return;
+
+       if (fd < 0)
+               ereport(FATAL,
+                               (errmsg("could not open file \"%s\" before fsync",
+                                               fname)));
+
+       pg_flush_data(fd, 0, 0);
+
+       close(fd);
+}
+
+/*
+ * walkdir: recursively walk a directory, applying the action to each
+ * regular file and directory (including the named directory itself)
+ * and following symbolic links.
+ *
+ * NB: There is another version of walkdir in initdb.c, but that version
+ * behaves differently with respect to symbolic links.  Caveat emptor!
+ */
+void
+walkdir(char *path, void (*action) (char *fname, bool isdir))
+{
+       DIR                *dir;
+       struct dirent *de;
+
+       dir = AllocateDir(path);
+       while ((de = ReadDir(dir, path)) != NULL)
+       {
+               char            subpath[MAXPGPATH];
+               struct stat fst;
+
+               CHECK_FOR_INTERRUPTS();
+
+               if (strcmp(de->d_name, ".") == 0 ||
+                       strcmp(de->d_name, "..") == 0)
+                       continue;
+
+               snprintf(subpath, MAXPGPATH, "%s/%s", path, de->d_name);
+
+               if (lstat(subpath, &fst) < 0)
+                       ereport(ERROR,
+                                       (errcode_for_file_access(),
+                                        errmsg("could not stat file \"%s\": %m", subpath)));
+
+               if (S_ISREG(fst.st_mode))
+                       (*action) (subpath, false);
+               else if (S_ISDIR(fst.st_mode))
+                       walkdir(subpath, action);
+#ifndef WIN32
+               else if (S_ISLNK(fst.st_mode))
+#else
+               else if (pg_win32_is_junction(subpath))
+#endif
+               {
+#if defined(HAVE_READLINK) || defined(WIN32)
+                       char            linkpath[MAXPGPATH];
+                       int                     len;
+                       struct stat lst;
+
+                       len = readlink(subpath, linkpath, sizeof(linkpath)-1);
+                       if (len < 0)
+                               ereport(ERROR,
+                                               (errcode_for_file_access(),
+                                                errmsg("could not read symbolic link \"%s\": %m",
+                                                               subpath)));
+
+                       if (len >= sizeof(linkpath)-1)
+                               ereport(ERROR,
+                                               (errmsg("symbolic link \"%s\" target is too long",
+                                                               subpath)));
+
+                       linkpath[len] = '\0';
+
+                       if (lstat(linkpath, &lst) == 0)
+                       {
+                               if (S_ISREG(lst.st_mode))
+                                       (*action) (linkpath, false);
+                               else if (S_ISDIR(lst.st_mode))
+                                       walkdir(subpath, action);
+                       }
+                       else if (errno != ENOENT)
+                               ereport(ERROR,
+                                               (errcode_for_file_access(),
+                                                errmsg("could not stat file \"%s\": %m", linkpath)));
+#else
+                       ereport(WARNING,
+                                       (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+                                        errmsg("this platform does not support symbolic links; ignoring \"%s\"",
+                                                       subpath)));
+#endif
+               }
+       }
+       FreeDir(dir);
+
+       (*action) (path, true);
+}

diff --git a/src/include/storage/fd.h b/src/include/storage/fd.h
index a6df8fb5a3a092a01f67e0498335c5532d9df394..435c37964f9092592706d3d86257c4b48ad30330 100644 (file)
--- a/src/include/storage/fd.h
+++ b/src/include/storage/fd.h
@@ -114,6 +114,8 @@ 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));
 
 /* Filename components for OpenTemporaryFile */
 #define PG_TEMP_FILES_DIR "pgsql_tmp"