| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com> |
| Cc: | Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Jason Petersen <jason(at)citusdata(dot)com>, PostgreSQL mailing lists <pgsql-bugs(at)postgresql(dot)org> |
| Subject: | Re: Concurrent ALTER SEQUENCE RESTART Regression |
| Date: | 2017-05-02 15:41:48 |
| Message-ID: | 20170502154148.scik2utyqtkyfinb@alap3.anarazel.de |
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| Lists: | pgsql-bugs pgsql-hackers |
On 2017-05-02 11:05:38 -0400, Peter Eisentraut wrote:
> On 4/27/17 01:52, Andres Freund wrote:
> > In contrast to <v10, the actual change of the tuple is *not* happening
> > with the page lock held. But now we do log XLOG_SEQ_LOG, then unlock
> > the buffer, and then do a CatalogTupleUpdate(). How is that correct?
>
> The change to the sequence data and the change to the catalog are two
> separate operations. There is no need AFAICT for the latter to be done
> while the former is locked or vice versa.
You snipped the salient part of my response:
> Imagine two of these running concurrently - you might end up with
> A:XLogInsert B:XLogInsert B:CatalogTupleUpdate A:CatalogTupleUpdate
Which'll lead, yet another avenue, to sequence states that aren't in
sync with the catalog.
- Andres
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