From: | Kevin Grittner <kgrittn(at)gmail(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Ian Jackson <ian(dot)jackson(at)eu(dot)citrix(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, xen-devel(at)lists(dot)xenproject(dot)org, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: [OSSTEST PATCH 0/1] PostgreSQL db: Retry on constraint violation [and 2 more messages] |
Date: | 2016-12-14 14:40:32 |
Message-ID: | CACjxUsM_GXTFwMGRhDKCUCxeSqk4jrhRM7aMt7QRoY5mPegbzg@mail.gmail.com |
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On Wed, Dec 14, 2016 at 8:27 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> But even after that fix, at the least, you'll still be able to
> demonstrate the same problem by trapping serialization_failure rather
> than unique_constraint.
I hope not; the "doomed" flag associated with a serializable
transaction should cause another attempt to cancel the transaction
at every subsequent opportunity, including commit. While we're
digging into bugs in this area it wouldn't hurt (as I said in my
prior post) to confirm that this is being handled everywhere it
should be, but I'd be kinda surprised if it wasn't.
> imagine a transaction that queries pg_stat_activity or
> pg_locks and then makes decisions based on the contents thereof. That
> transaction is determined to behave different under concurrency than
> it does on an idle system, and even the ineluctable triumvirate of
> Kevin Grittner, Dan Ports, and Michael Cahill will not be able to
> prevent it from doing so. That's not a bug.
OK, I'll agree that it may be theoretically possible to create some
sort of "side channel" for seeing data which subverts
serializability in some arcane way. I would agree that's not a bug
any more than limited data that is unavoidably leaked through
security barriers is. I don't think that subtransactions should
rise to that level, though.
--
Kevin Grittner
EDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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