Re: Two issues with REFRESH MATERIALIZED VIEW CONCURRENTLY

Hi All,

Also, for issue 1, additional test case should be added.
>
Sure, I will add test cases for issue 1.

For issue 2, it would be helpful if you may share some performance numbers
> to confirm if this solution is only improving the performance and not
> causing any regressions.
>
I ran check, check-world and didn't see any regressions.

Here is the output and performance improvement:
>>
>> postgres=# \timing on
>>
>> Timing is on.
>>
>> postgres=# DROP MATERIALIZED VIEW IF EXISTS s CASCADE;
>>
>> NOTICE: materialized view "s" does not exist, skipping
>>
>> DROP MATERIALIZED VIEW
>>
>> Time: 0.858 ms
>>
>> postgres=#
>>
>> postgres=# CREATE MATERIALIZED VIEW s AS SELECT generate_series as x,
>> null as y FROM generate_series(1, 1000000);
>>
>> SELECT 1000000
>>
>> Time: 1076.254 ms (00:01.076)
>>
>> postgres=#
>>
>> postgres=# CREATE UNIQUE INDEX ON s(x);
>>
>> CREATE INDEX
>>
>> Time: 375.026 ms
>>
>> postgres=# REFRESH MATERIALIZED VIEW CONCURRENTLY s;
>>
>> REFRESH MATERIALIZED VIEW
>>
>> Time: 3807.143 ms (00:03.807)
>>
>> postgres=# CREATE UNIQUE INDEX ON s(y);
>>
>> CREATE INDEX
>>
>> Time: 331.382 ms
>>
>> postgres=# REFRESH MATERIALIZED VIEW CONCURRENTLY s;
>>
>> REFRESH MATERIALIZED VIEW
>>
>> Time: 3636.049 ms (00:03.636)
>> postgres=#
>>
>> As we can see the REFRESH MATERIALIZED VIEW CONCURRENTLY now takes 3636.049
>> ms
>>
> Regrading the performance, (quoting the output from my previous message)
with unique index having NULL values we see that both "REFRESH MATERIALIZED
VIEW CONCURRENTLY s;" operations (operation 1 was after CREATE UNIQUE INDEX
ON s(x); and operation 2 was after CREATE UNIQUE INDEX ON s(x);) take about
the same time. Without the patch, operation 2 was taking around ~11000
ms, due to NULL = NULL comparison checks and this was causing the
degradation.

Regarding different commits to each issue, I don't have any
particular opinion but since both the issues are related to the same
function and NULL comparison, I feel we can have a single commit, but open
to create 2 commits too.

Regards,
Surya Poondla