Re: regression, deadlock in high frequency single-row UPDATE

On 12/12/14 06:22, Alvaro Herrera wrote:

> Before this can be committed I need an isolationtester spec file that
> reproduces the problem. Now that I understand why it happens it should
> be easy to produce: just have a transaction that does BEGIN, then the
> insert, and keeps the transaction open; enough other sessions run the
> UPDATE until the problem pops up. (Also, comments on
> Would_MultiXactIdWait_Block need work.)
>

FWIW - I was having a look at the isolationtester spec. Playing with the
pgbench setup to see the minimal number of session I needed to provoke
the deadlock (unpatched 9.5 code) seemed to converge to about 4. I
managed to still see 1 deadlock with each session only doing 1
transaction - i.e:

$ pgbench -c 4 -C -n -t 1 -f query.sql deadlock

...which resulted in 1 deadlock. So we may be able to get a reasonable
test case that shows this up! I'll take a look at setting up a test case
later - but don't let that stop you doing it 1st :-)

Cheers

Mark