Re: Feature: triggers on materialized views

Hi!

False alarm. It just looks like updating patches takes longer than
updating e-mails.


Mitar

On Fri, Dec 28, 2018 at 12:11 AM Mitar <mmitar@gmail.com> wrote:
>
> Hi!
>
> Hm, why in commitfest it does not display the latest patch?
>
> https://commitfest.postgresql.org/21/1953/
>
> It does display correctly the latest e-mail, but not the link to the patch. :-(
>
>
> Mitar
>
> On Thu, Dec 27, 2018 at 11:51 PM Mitar <mmitar@gmail.com> wrote:
> >
> > Hi!
> >
> > One more version of the patch with slightly more deterministic tests.
> >
> >
> > Mitar
> >
> > On Thu, Dec 27, 2018 at 11:43 PM Mitar <mmitar@gmail.com> wrote:
> > >
> > > Hi!
> > >
> > > I have made an updated version of the patch, added tests and
> > > documentation changes. This is my view now a complete patch. Please
> > > provide any feedback or comments you might have for me to improve the
> > > patch. I will also add it to commitfest.
> > >
> > > A summary of the patch: This patch enables adding AFTER triggers (both
> > > ROW and STATEMENT) on materialized views. They are fired when doing
> > > REFRESH MATERIALIZED VIEW CONCURRENTLY for rows which have changed.
> > > Triggers are not fired if you call REFRESH without CONCURRENTLY. This
> > > is based on some discussion on the mailing list because implementing
> > > it for without CONCURRENTLY would require us to add logic for firing
> > > triggers where there was none before (and is just an efficient heap
> > > swap).
> > >
> > > To be able to create a materialized view without data, specify
> > > triggers, and REFRESH CONCURRENTLY so that those triggers would be
> > > called also for initial data, I have tested and determined that there
> > > is no reason why REFRESH CONCURRENTLY could not be run on
> > > uninitialized materialized view. So I removed that check and things
> > > seem to just work. Including triggers being called for initial data. I
> > > think this makes REFRESH CONCURRENTLY have one less special case which
> > > is in general nicer.
> > >
> > > I have run tests and all old tests still succeed. I have added more
> > > tests for the new feature.
> > >
> > > I have run benchmark to evaluate the impact of me changing
> > > refresh_by_match_merge to do UPDATE instead of DELETE and INSERT for
> > > rows which were just updated. In fact it seems this improves
> > > performance slightly (4% in my benchmark, mean over 10 runs). I guess
> > > that this is because it is cheaper to just change one column's values
> > > (what benchmark is doing when changing rows) instead of removing and
> > > inserting the whole row. Because REFRESH MATERIALIZED VIEW
> > > CONCURRENTLY is meant to be used when not a lot of data has been
> > > changed anyway, I find this a pleasantly surprising additional
> > > improvement in this patch. I am attaching the benchmark script I have
> > > used. I compared the time of the final refresh query in the script. (I
> > > would love if pgbench could take a custom init script to run before
> > > the timed part of the script.)
> > >
> > >
> > > Mitar
> > >
> > > On Mon, Dec 24, 2018 at 12:59 PM Mitar <mmitar@gmail.com> wrote:
> > > >
> > > > Hi!
> > > >
> > > > Based on discussion about observing changes on an open query in a
> > > > reactive manner (to support reactive web applications) [1], I
> > > > identified that one critical feature is missing to fully implement
> > > > discussed design of having reactive queries be represented as
> > > > materialized views, and changes to these materialized views would then
> > > > be observed and pushed to the client through LISTEN/NOTIFY.
> > > >
> > > > This is my first time contributing to PostgreSQL, so I hope I am
> > > > starting this process well.
> > > >
> > > > I would like to propose that support for AFTER triggers are added to
> > > > materialized views. I experimented a bit and it seems this is mostly
> > > > just a question of enabling/exposing them. See attached patch. This
> > > > enabled me to add trigger to a material view which mostly worked. Here
> > > > are my findings.
> > > >
> > > > Running REFRESH MATERIALIZED VIEW CONCURRENTLY calls triggers. Both
> > > > per statement and per row. There are few improvements which could be
> > > > done:
> > > >
> > > > - Currently only insert and remove operations are done on the
> > > > materialized view. This is because the current logic just removes
> > > > changed rows and inserts new rows.
> > > > - In current concurrently refresh logic those insert and remove
> > > > operations are made even if there are no changes to be done. Which
> > > > triggers a statement trigger unnecessary. A small improvement could be
> > > > to skip the statement in that case, but looking at the code this seems
> > > > maybe tricky because both each of inserts and deletions are done
> > > > inside one query each.
> > > > - Current concurrently refresh logic does never do updates on existing
> > > > rows. It would be nicer to have that so that triggers are more aligned
> > > > with real changes to the data. So current two queries could be changed
> > > > to three, each doing one of the insert, update, and delete.
> > > >
> > > > Non-concurrent refresh does not trigger any trigger. But it seems all
> > > > data to do so is there (previous table, new table), at least for the
> > > > statement-level trigger. Row-level triggers could also be simulated
> > > > probably (with TRUNCATE and INSERT triggers).
> > > >
> > > > [1]
https://www.postgresql.org/message-id/flat/CAKLmikP%2BPPB49z8rEEvRjFOD0D2DV72KdqYN7s9fjh9sM_32ZA%40mail.gmail.com
> > > >
> > > >
> > > > Mitar
> > > >
> > > > --
> > > > http://mitar.tnode.com/
> > > > https://twitter.com/mitar_m
> > >
> > >
> > >
> > > --
> > > http://mitar.tnode.com/
> > > https://twitter.com/mitar_m
> >
> >
> >
> > --
> > http://mitar.tnode.com/
> > https://twitter.com/mitar_m
>
>
>
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