| From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Reviewing freeze map code |
| Date: | 2016-06-23 22:59:57 |
| Message-ID: | 20160623225957.GA230122@alvherre.pgsql |
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| Lists: | pgsql-hackers |
Andres Freund wrote:
> I'm looking into three approaches right now:
>
> 3) Use WAL logging for the already_marked = true case.
> 3) This approach so far seems the best. It's possible to reuse the
> xl_heap_lock record (in an afaics backwards compatible manner), and in
> most cases the overhead isn't that large. It's of course annoying to
> emit more WAL, but it's not that big an overhead compared to extending a
> file, or to toasting. It's also by far the simplest fix.
I suppose it's fine if we crash midway from emitting this wal record and
the actual heap_update one, since the xmax will appear to come from an
aborted xid, right?
I agree that the overhead is probably negligible, considering that this
only happens when toast is invoked. It's probably not as great when the
new tuple goes to another page, though.
--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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