When pg_basebackup copies data files, it does basically this:
if (lstat(pathbuf, &statbuf) != 0)
{
if (errno != ENOENT)
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not stat file or directory \"%s\":
%m",
pathbuf)));
/* If the file went away while scanning, it's no error. */
continue;
}
> ...
> sendFile(pathbuf, pathbuf + basepathlen + 1, &statbuf);
There's a race condition there. If the file is removed after the lstat
call, and before sendFile opens the file, the backup fails with an
error. It's a fairly tight window, so it's difficult to run into by
accident, but by putting a breakpoint with a debugger there it's quite
easy to reproduce, by e.g doing a VACUUM FULL on the table about to be
copied.
A straightforward fix is to allow sendFile() to ignore ENOENT. Patch
attached.
- Heikki
diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 1b234c6..bc95215 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -44,8 +44,8 @@ typedef struct
static int64 sendDir(char *path, int basepathlen, bool sizeonly);
-static void sendFile(char *readfilename, char *tarfilename,
- struct stat * statbuf);
+static bool sendFile(char *readfilename, char *tarfilename,
+ struct stat * statbuf, bool missing_ok);
static void sendFileWithContent(const char *filename, const char *content);
static void _tarWriteHeader(const char *filename, const char *linktarget,
struct stat * statbuf);
@@ -194,7 +194,7 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
XLOG_CONTROL_FILE)));
}
- sendFile(XLOG_CONTROL_FILE, XLOG_CONTROL_FILE, &statbuf);
+ sendFile(XLOG_CONTROL_FILE, XLOG_CONTROL_FILE, &statbuf, false);
}
/*
@@ -715,11 +715,18 @@ sendDir(char *path, int basepathlen, bool sizeonly)
}
else if (S_ISREG(statbuf.st_mode))
{
- /* Add size, rounded up to 512byte block */
- size += ((statbuf.st_size + 511) & ~511);
+ bool sent = false;
+
if (!sizeonly)
- sendFile(pathbuf, pathbuf + basepathlen + 1, &statbuf);
- size += 512; /* Size of the header of the file */
+ sent = sendFile(pathbuf, pathbuf + basepathlen + 1, &statbuf,
+ true);
+
+ if (sent || sizeonly)
+ {
+ /* Add size, rounded up to 512byte block */
+ size += ((statbuf.st_size + 511) & ~511);
+ size += 512; /* Size of the header of the file */
+ }
}
else
ereport(WARNING,
@@ -779,9 +786,17 @@ _tarChecksum(char *header)
return sum;
}
-/* Given the member, write the TAR header & send the file */
-static void
-sendFile(char *readfilename, char *tarfilename, struct stat * statbuf)
+/*
+ * Given the member, write the TAR header & send the file.
+ *
+ * If 'missing_ok' is true, will not throw an error if the file is not found.
+ *
+ * Returns true if the file was successfully sent, false if 'missing_ok',
+ * and the file did not exist.
+ */
+static bool
+sendFile(char *readfilename, char *tarfilename, struct stat *statbuf,
+ bool missing_ok)
{
FILE *fp;
char buf[TAR_SEND_SIZE];
@@ -791,9 +806,13 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf)
fp = AllocateFile(readfilename, "rb");
if (fp == NULL)
+ {
+ if (errno == ENOENT && missing_ok)
+ return false;
ereport(ERROR,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m", readfilename)));
+ }
/*
* Some compilers will throw a warning knowing this test can never be true
@@ -847,6 +866,8 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf)
}
FreeFile(fp);
+
+ return true;
}
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