small parallel restore optimization

Here's a little optimization for the parallel restore code, that 
inhibits reopening the archive file unless the worker will actually need 
to read from the file (i.e. a data member). It seems to work OK on both 
Linux and Windows, and I propose to apply it in a day or two.

I've seen a recent error that suggests we are clobbering memory 
somewhere in the parallel code, as well as Olivier Prennant's reported 
error that suggests the same thing, although I'm blessed if I can see 
where it might be. Maybe some more eyeballs on the code would help.


cheers

andrew





Index: pg_backup_archiver.c
===================================================================
RCS file: /cvsroot/pgsql/src/bin/pg_dump/pg_backup_archiver.c,v
retrieving revision 1.165
diff -c -u -r1.165 pg_backup_archiver.c
cvs diff: conflicting specifications of output style
--- pg_backup_archiver.c        5 Mar 2009 14:51:10 -0000       1.165
+++ pg_backup_archiver.c        6 Mar 2009 16:51:41 -0000
@@ -3471,8 +3471,11 @@
         *
         * Note: on Windows, since we are using threads not processes, this
         * *doesn't* close the original file pointer but just open a new 
one.
+        *
+        * Only do this if we actually need to read the file for data.
         */
-       (AH->ReopenPtr) (AH);
+       if ( te->section == SECTION_DATA )
+          (AH->ReopenPtr) (AH);
 
        /*
         * We need our own database connection, too
@@ -3490,7 +3493,9 @@
        PQfinish(AH->connection);
        AH->connection = NULL;
 
-       (AH->ClosePtr) (AH);
+       /* close the file if we reopened it */
+       if ( te->section == SECTION_DATA )
+          (AH->ClosePtr) (AH);
 
        if (retval == 0 && AH->public.n_errors)
           retval = WORKER_IGNORED_ERRORS;