Fix race condition if a file is removed while pg_basebackup is running.

If a relation file was removed when the server-side counterpart of
pg_basebackup was just about to open it to send it to the client, you'd
get a "could not open file" error. Fix that.

Backpatch to 9.1, this goes back to when pg_basebackup was introduced.

diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 41cab5b0ffa55201319e879b3ae27fd6cfb240ae..610a799400c43b614cd4e65449783c68b3fcf188 100644 (file)
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -43,8 +43,8 @@ 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);
@@ -692,11 +692,18 @@ 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,
@@ -756,9 +763,17 @@ _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];
@@ -768,9 +783,13 @@ 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
@@ -824,6 +843,8 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf)
    }
 
    FreeFile(fp);
+
+   return true;
 }