Re: WIP Patch: Pgbench Serialization and deadlock errors

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Marina Polyakova <m(dot)polyakova(at)postgrespro(dot)ru>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgresql(dot)org>, Kevin Grittner <kgrittn(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>
Subject: Re: WIP Patch: Pgbench Serialization and deadlock errors
Date: 2017-07-14 11:58:21
Message-ID: alpine.DEB.2.20.1707141344070.20175@lancre
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Hello Marina,

>> Not necessarily? It depends on where the locks triggering the issue
>> are set, if they are all set after the savepoint it could work on a
>> second attempt.
> Don't you mean the deadlock failures where can really help rollback to

Yes, I mean deadlock failures can rollback to a savepoint and work on a
second attempt.

> And could you, please, give an example where a rollback to savepoint can
> help to end its subtransaction successfully after a serialization
> failure?

I do not know whether this is possible with about serialization failures.
It might be if the stuff before and after the savepoint are somehow

> [...] I mean that the sum of transactions with serialization failure and
> transactions with deadlock failure can be greater then the totally sum
> of transactions with failures.

Hmmm. Ok.

A "failure" is a transaction (in the sense of pgbench) that could not made
it to the end, even after retries. If there is a rollback and the a retry
which works, it is not a failure.

Now deadlock or serialization errors, which trigger retries, are worth
counting as well, although they are not "failures". So my format proposal
was over optimistic, and the number of deadlocks and serializations should
better be on a retry count line.

Maybe something like:
number of failures: 12 (0.004%)
number of retries: 64 (deadlocks: 29, serialization: 35)


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