On 9/6/07, Tom Lane <[EMAIL PROTECTED]> wrote: > > "Heikki Linnakangas" <[EMAIL PROTECTED]> writes: > > When I suggested that we get rid of the LP_DELETE flag for heap tuples, > > the tuple-level fragmentation and all that, and just take the vacuum > > lock and call PageRepairFragmentation, I was thinking that we'd do it in > > heap_update and only when we run out of space on the page. But as Greg > > said, it doesn't work because you're already holding a reference to at > > least one tuple on the page, the one you're updating, by the time you > > get to heap_update. That's why I put the pruning code to heap_fetch > > instead. Yes, though the amortized cost is the same, it does push the > > pruning work to the foreground query path. > > The amortized cost is only "the same" if every heap_fetch is associated > with a heap update. I feel pretty urgently unhappy about this choice. > Have you tested the impact of the patch on read-mostly workloads? > > For read-mostly workloads, only the first SELECT after an UPDATE would trigger pruning/defragmentation. heap_page_prune_defrag() would be a no-op for subsequent SELECTs (PageIsPrunable() would be false until the next UPDATE)
I think Heikki's recent test confirms this. Thanks, Pavan -- Pavan Deolasee EnterpriseDB http://www.enterprisedb.com
