On Mon, Oct 28, 2019 at 6:08 PM Dilip Kumar <dilipbal...@gmail.com> wrote: > > On Fri, Oct 25, 2019 at 9:19 PM Masahiko Sawada <sawada.m...@gmail.com> wrote: > > > > On Fri, Oct 25, 2019 at 2:06 PM Dilip Kumar <dilipbal...@gmail.com> wrote: > > > > > > On Fri, Oct 25, 2019 at 10:22 AM Masahiko Sawada <sawada.m...@gmail.com> > > > wrote: > > > > > > > > For more detail of my idea it is that the first worker who entered to > > > > vacuum_delay_point adds its local value to shared value and reset the > > > > local value to 0. And then the worker sleeps if it exceeds > > > > VacuumCostLimit but before sleeping it can subtract VacuumCostLimit > > > > from the shared value. Since vacuum_delay_point are typically called > > > > per page processed I expect there will not such problem. Thoughts? > > > > > > Oh right, I assumed that when the local balance is exceeding the > > > VacuumCostLimit that time you are adding it to the shared value but > > > you are adding it to to shared value every time in vacuum_delay_point. > > > So I think your idea is correct. > > > > I've attached the updated patch set. > > > > First three patches add new variables and a callback to index AM. > > > > Next two patches are the main part to support parallel vacuum. I've > > incorporated all review comments I got so far. The memory layout of > > variable-length index statistics might be complex a bit. It's similar > > to the format of heap tuple header, having a null bitmap. And both the > > size of index statistics and actual data for each indexes follows. > > > > Last patch is a PoC patch that implements the shared vacuum cost > > balance. For now it's separated but after testing both approaches it > > will be merged to 0004 patch. I'll test both next week. > > > > This patch set can be applied on top of the patch[1] that improves > > gist index bulk-deletion. So canparallelvacuum of gist index is true. > > > > + /* Get the space for IndexBulkDeleteResult */ > + bulkdelete_res = GetIndexBulkDeleteResult(shared_indstats); > + > + /* > + * Update the pointer to the corresponding bulk-deletion result > + * if someone has already updated it. > + */ > + if (shared_indstats->updated && stats[idx] == NULL) > + stats[idx] = bulkdelete_res; > + > > I have a doubt in this hunk, I do not understand when this condition > will be hit? Because whenever we are setting shared_indstats->updated > to true at the same time we are setting stats[idx] to shared stat. So > I am not sure in what case the shared_indstats->updated will be true > but stats[idx] is still pointing to NULL? >
I think it can be true in the case where one parallel vacuum worker vacuums the index that was vacuumed by other workers in previous index vacuum cycle. Suppose that worker-A and worker-B vacuumed index-A and index-B respectively. After that worker-A vacuum index-B in the next index vacuum cycle. In this case, shared_indstats->updated is true because worker-B already vacuumed in the previous vacuum cycle. On the other hand stats[idx] on worker-A is NULL because it's first time for worker-A to vacuum index-B. Therefore worker-A updates its stats[idx] to the bulk-deletion result on DSM in order to pass it to the index AM. Regards, -- Masahiko Sawada
