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Re: Re: new patch of MERGE (merge_204) & a question about duplicated ctid

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>,Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>,Greg Smith <greg(at)2ndquadrant(dot)com>,Marko Tiikkaja <marko(dot)tiikkaja(at)cs(dot)helsinki(dot)fi>,Boxuan Zhai <bxzhai2010(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Re: new patch of MERGE (merge_204) & a question about duplicated ctid
Date: 2011-01-03 15:56:27
Message-ID: 20110103155627.GI4933@tamriel.snowman.net (view raw or flat)
Thread:
Lists: pgsql-hackers
* Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
> Like Heikki, I'd rather have the feature without a workaround for the
> concurrency issues than no feature.

I'm still trying to figure out the problem with having the table-level
lock, unless we really think people will be doing concurrent MERGE's
where they won't overlap..?  I'm also a bit nervous about if the result
of concurrent MERGE's would actually be correct if we're not taking a
bigger lock than row-level (I assume we're taking row-level locks as it
goes through..).

In general, I also thought/expected to have some kind of UPSERT type
capability with our initial MERGE support, even if it requires a big
lock and won't operate concurrently, etc.

> But I have to admit that the
> discussion we've had thus far gives me very little confidence that
> this code is anywhere close to bug-free.  So I think we're going to
> end up punting it to 9.2 not so much because it's not concurrency-safe
> as because it doesn't work.

That's certainly a concern. :/

	Stephen

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Next:From: Heikki LinnakangasDate: 2011-01-03 15:58:44
Subject: Re: Re: new patch of MERGE (merge_204) & a question about duplicated ctid
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Subject: Re: Scanning pg_tablespace from walsender

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