Re: serializable transaction: exclude constraint violation (backed by GIST index) instead of ssi conflict

On Thu, Apr 11, 2019 at 10:54 AM Thomas Munro <thomas(dot)munro(at)gmail(dot)com> wrote:
> On Thu, Apr 11, 2019 at 9:43 AM Peter Billen <peter(dot)billen(at)gmail(dot)com> wrote:
> > I kinda expected/hoped that transaction t2 would get aborted by a serialization error, and not an exclude constraint violation. This makes the application session bound to transaction t2 failing, as only serialization errors are retried.

> Yeah, I agree, the behaviour you are expecting is desirable and we
> should figure out how to do that. The basic trick for btree unique
> constraints was to figure out where the index *would* have written, to
> give the SSI machinery a chance to object to that before raising the
> UCV. I wonder if we can use the same technique here... at first
> glance, check_exclusion_or_unique_constraint() is raising the error,
> but is not index AM specific code, and it is somewhat removed from the
> GIST code that would do the equivalent
> CheckForSerializableConflictIn() call. I haven't looked into it
> properly, but that certainly complicates matters somewhat... Perhaps
> the index AM would actually need a new entrypoint that could be called
> before the error is raised, or perhaps there is an easier way.

Adding Kevin (architect of SSI and reviewer/committer of my UCV
interception patch) and Shubham (author of GIST SSI support) to the CC
list in case they have thoughts on this.

--
Thomas Munro
https://enterprisedb.com