Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

On Sun, Dec 29, 2019 at 1:34 PM Dilip Kumar <dilipbalaut(at)gmail(dot)com> wrote:
> On Sat, Dec 28, 2019 at 9:33 PM Tomas Vondra
> <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
> >
> >
> > Yeah, the "is_schema_sent" flag in ReorderBufferTXN does not work - it
> > needs to be in the RelationSyncEntry. In fact, I already have code for
> > that in my private repository - I thought the patches I sent here do
> > include this, but apparently I forgot to include this bit :-(
> >
> > Attached is a rebased patch series, fixing this. It's essentially v2
> > with a couple of patches (0003, 0008, 0009 and 0012) replacing the
> > is_schema_sent with correct handling.
> >
> >
> > 0003 - removes an is_schema_sent reference added prematurely (it's added
> > by a later patch, causing compile failure)
> >
> > 0008 - adds the is_schema_sent back (essentially reverting 0003)
> >
> > 0009 - removes is_schema_sent entirely
> >
> > 0012 - adds the correct handling of schema flags in pgoutput
> >

Thanks for splitting the changes. They are quite clear.

> >
> > I don't know what other changes you've made since v2, so this way it
> > should be possible to just take 0003, 0008, 0009 and 0012 and slip them
> > in with minimal hassle.
> >
> > FWIW thanks to everyone (and Amit and Dilip in particular) working on
> > this patch series. There's been a lot of great reviews and improvements
> > since I abandoned this thread for a while. I expect to be able to spend
> > more time working on this in January.
> >
> +static void
> +set_schema_sent_in_streamed_txn(RelationSyncEntry *entry, TransactionId xid)
> +{
> + MemoryContext oldctx;
> +
> + oldctx = MemoryContextSwitchTo(CacheMemoryContext);
> +
> + entry->streamed_txns = lappend_int(entry->streamed_txns, xid);
> +
> + MemoryContextSwitchTo(oldctx);
> +}
> I was looking into the schema tracking solution and I have one
> question, Shouldn't we remove the topxid from the list if the
> (sub)transaction is aborted? because once it is aborted we need to
> resent the schema.
>

I think you are right because, at abort, the subscriber would remove
the changes (for a subtransaction) including the schema changes sent
and then it won't be able to understand the subsequent changes sent by
the publisher. Won't we need to remove xid from the list at commit
time as well, otherwise, the list will keep on growing. One more
thing, we need to search the list of all the relations in the local
map to find xid being aborted/committed, right? If so, won't it be
costly doing at each transaction abort/commit?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com