> On Mon, 29 Oct 2018 at 05:56, Haribabu Kommi <kommi.haribabu@gmail.com> wrote:
>
>> This problem couldn't be reproduced on the master branch, so I've tried to
>> investigate it. It comes from nodeModifyTable.c:1267, when we've got
>> HeapTupleInvisible as a result, and this value in turn comes from
>> table_lock_tuple. Everything points to the new way of handling HeapTupleUpdated
>> result from heap_update, when table_lock_tuple call was introduced. Since I
>> don't see anything similar in the master branch, can anyone clarify why is this
>> lock necessary here?
>
>
> In the master branch code also, there is a tuple lock that is happening in
> EvalPlanQual() function, but pluggable-storage code, the lock is kept outside
> and also function call rearrangements, to make it easier for the table access
> methods to provide their own MVCC implementation.
Yes, now I see it, thanks. Also I can confirm that the attached patch solves
this issue.
Thanks for the testing and confirmation.
FYI, alongside with reviewing the code changes I've ran few performance tests
(that's why I hit this issue with pgbench in the first place). In case of high
concurrecy so far I see small performance degradation in comparison with the
master branch (about 2-5% of average latency, depending on the level of
concurrency), but can't really say why exactly (perf just shows barely
noticeable overhead there and there, maybe what I see is actually a cumulative
impact).
Thanks for sharing your observation, I will also analyze and try to find out performance
bottlenecks that are causing the overhead.
Here I attached the cumulative fixes of the patches, new API additions for zheap and
basic outline of the documentation.
Regards,
Haribabu Kommi
Fujitsu Australia