Re: [Xen-devel] [HACKERS] [OSSTEST PATCH 0/1] PostgreSQL db: Retry on constraint violation [and 2 more messages]

[Kevin Grittner <kgrittn@xxxxxxxxx>]

On Wed, Dec 14, 2016 at 8:27 AM, Robert Haas <robertmhaas@xxxxxxxxx> 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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