On 3 December 2012 17:37, Pavan Deolasee <pavan.deolasee@gmail.com> wrote:
> I was looking at the code when the following tiny bit caught my attention.
> In vacuumlazy.c, we release the pin on the final VM page at line number 972.
>
> 954 if (vacrelstats->num_dead_tuples > 0)
> 955 {
> 956 /* Log cleanup info before we touch indexes */
> 957 vacuum_log_cleanup_info(onerel, vacrelstats);
> 958
> 959 /* Remove index entries */
> 960 for (i = 0; i < nindexes; i++)
> 961 lazy_vacuum_index(Irel[i],
> 962 &indstats[i],
> 963 vacrelstats);
> 964 /* Remove tuples from heap */
> 965 lazy_vacuum_heap(onerel, vacrelstats);
> 966 vacrelstats->num_index_scans++;
> 967 }
> 968
> 969 /* Release the pin on the visibility map page */
> 970 if (BufferIsValid(vmbuffer))
> 971 {
> 972 ReleaseBuffer(vmbuffer);
> 973 vmbuffer = InvalidBuffer;
> 974 }
>
> So we are holding the pin right through the index vacuuming and the second
> pass over the heap; both can take a very long time. We can and should really
> be releasing the pin *before* those steps. In fact, it would be appropriate
> to do it right after the preceding big for-loop.
>
> While it may or may not matter from the performance or correctness
> perspective, I think we should fix that.
Yes, its a clear bug. Patched.
-- Simon Riggs http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services
