Re: parallel pg_restore - WIP patch

On Fri, 26 Sep 2008 17:10:44 -0400
Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:

> Yes, there are several funny things going on, including some stuff
> with dependencies. I'll have a new patch tomorrow with luck. Thanks
> for testing.

O.k. I took at look at the patch itself and although I don't understand
all of it there were a couple of red flags to me:

+ if (ropt->create)
+ die_horribly(AH,modulename,
+ "parallel restore is
incompatible with --create\n");
+

This seems like an odd limitation. In my mind, the schema would not be
restored in parallel. The schema before data would restore as a single
thread. Even the largest schemas would only take minutes (if that).
Thus something like --create should never be a problem.

I also noticed you check if we have zlib? Is it even possible to use
the c format without it? (that would be new to me).

I noticed this line:

+ while((next_work_item = get_next_work_item(AH)) != NULL)
+ {
+ /* XXX need to improve this test in case there is no
table data */
+ /* need to test for indexes, FKs, PK, Unique, etc */
+ if(strcmp(next_work_item->desc,"TABLE DATA") == 0)
+ break;
+ (void) _restore_one_te(AH, next_work_item, ropt,
false);
+
+ next_work_item->prestored = true;
+
+ _reduce_dependencies(AH,next_work_item);
+ }

Intead of the TABLE DATA compare, perhaps it makes sense to back patch
pg_dump to have a line delimiter in the TOC? That way even if there is
no TABLE DATA there would be a delimiter that says:

--- BEGIN TABLE DATA
--- END TABLE DATA

Thus if nothing is there... nothing is there?

+ /* delay just long enough betweek forks to
give the catalog some
+ * breathing space. Without this sleep I got
+ * "tuple concurrently updated" errors.
+ */
+ pg_usleep(500000);
+ continue; /* in case the slots are not yet
full */
+ }

Could that be solved with a lock instead? Once the lock is released....

Anyway... just some thoughts. I apologize if I misunderstood the patch.

Sincerely,

Joshua D. Drake

>
> cheers
>
> andrew
>

--
The PostgreSQL Company since 1997: http://www.commandprompt.com/
PostgreSQL Community Conference: http://www.postgresqlconference.org/
United States PostgreSQL Association: http://www.postgresql.us/