Re: Performance degradation of REFRESH MATERIALIZED VIEW

On Fri, Mar 12, 2021 at 3:13 AM Andres Freund <andres(at)anarazel(dot)de> wrote:
>
> Hi,
>
> On 2021-03-11 17:44:37 +0900, Masahiko Sawada wrote:
> > The execution time of REFRESH MATERIALIZED VIEW are:
> >
> > w/ HEAP_INSERT_FROZEN flag : 42 sec
> > w/o HEAP_INSERT_FROZEN flag : 33 sec
> >
> > After investigation, I found that such performance degradation happens
> > on only HEAD code. It seems to me that commit 39b66a91b (and
> > 7db0cd2145) is relevant that has heap_insert() set VM bits and
> > PD_ALL_VISIBLE if HEAP_INSERT_FROZEN is specified (so CCing Tomas
> > Vondra and authors). Since heap_insert() sets PD_ALL_VISIBLE to the
> > page when inserting a tuple for the first time on the page (around
> > L2133 in heapam.c), every subsequent heap_insert() on the page reads
> > and pins a VM buffer (see RelationGetBufferForTuple()). Reading and
> > pinning a VM buffer for every insertion is a very high cost. This
> > doesn't happen in heap_multi_insert() since it sets VM buffer after
> > filling the heap page with tuples. Therefore, there is no such
> > performance degradation between COPY and COPY FREEZE if they use
> > heap_multi_insert() (i.g., CIM_MULTI). Paul also reported it in that
> > thread.
>
> Probably worth adding as an open item for 14.

I've added it to PostgreSQL 14 Open Items.

Regards,

--
Masahiko Sawada
EDB: https://www.enterprisedb.com/