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  1. pg_stat_statements: track number of rows processed by REFRESH MATERIALIZED VIEW.

  1. REFRESH MATERIALIZED VIEW and completion tag output

    Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-11-05T16:20:04Z

    Hi,

The patch that makes pg_stat_statements track the number of rows that
REFRESH MATERIALIZED VIEW command processes was proposed at [1].
When reviewing the patch, I just wondered why the completion tag output
for REFRESH MATERIALIZED VIEW doesn't include the row count. Is this
an intentional behavior? I've not found the past discussion about this yet.

OTOH, CREATE MATERIALIZED VIEW reports something like "SELECT NNN"
(NNN is the row count) as the completion tag output. If WITH NO DATA is
specified, "CREATE MATERIALIZED VIEW" is reported instead. Is it better
to make REFRESH MATERIALIZED VIEW do the similar thing? Or we should
not do that, for example, since changing the completion tag output may
break the client app?

[1] https://postgr.es/m/71f6bc72f8bbaa06e701f8bd2562c347@oss.nttdata.com

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

  2. Re: REFRESH MATERIALIZED VIEW and completion tag output

    Mark Dilger <mark.dilger@enterprisedb.com> — 2020-11-05T16:56:43Z

    
> On Nov 5, 2020, at 8:20 AM, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> 
> The patch that makes pg_stat_statements track the number of rows that
> REFRESH MATERIALIZED VIEW command processes was proposed at [1].
> When reviewing the patch, I just wondered why the completion tag output
> for REFRESH MATERIALIZED VIEW doesn't include the row count. Is this
> an intentional behavior? I've not found the past discussion about this yet.

Of 191 command tags, only 7 return the number of rows.  See src/include/tcop/cmdtaglist.h.  REFRESH MATERIALIZED VIEW is similar to CREATE MATERIALIZED VIEW and also CREATE TABLE AS, which also do not return the row count.  I think this behavior is historical, and preserved for compatibility.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

  3. Re: REFRESH MATERIALIZED VIEW and completion tag output

    Fujii Masao <masao.fujii@oss.nttdata.com> — 2020-11-06T00:45:07Z

    
On 2020/11/06 1:56, Mark Dilger wrote:
> 
> 
>> On Nov 5, 2020, at 8:20 AM, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>
>> The patch that makes pg_stat_statements track the number of rows that
>> REFRESH MATERIALIZED VIEW command processes was proposed at [1].
>> When reviewing the patch, I just wondered why the completion tag output
>> for REFRESH MATERIALIZED VIEW doesn't include the row count. Is this
>> an intentional behavior? I've not found the past discussion about this yet.
> 
> Of 191 command tags, only 7 return the number of rows.  See src/include/tcop/cmdtaglist.h.  REFRESH MATERIALIZED VIEW is similar to CREATE MATERIALIZED VIEW and also CREATE TABLE AS, which also do not return the row count.

Yes, so I was wondering if REFRESH MATERIALIZED VIEW also should use
CMDTAG_SELECT like CREATE MATERIALIZED VIEW does.

>  I think this behavior is historical, and preserved for compatibility.

Maybe true. The patch that I mentioned upthread tries to change
REFRESH MATERIALIZED VIEW so that it register the rowcount into
its query completion so that pg_stat_statements can track
the number of processed rows. But display_rowcount for
CMDTAG_REFRESH_MATERIALIZED_VIEW still should be false
in cmdtaglist.h to avoid the change of the completion tag output.

Regards,

-- 
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION

  4. Re: REFRESH MATERIALIZED VIEW and completion tag output

    Mark Dilger <mark.dilger@enterprisedb.com> — 2020-11-06T05:07:27Z

    
> On Nov 5, 2020, at 4:45 PM, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
> 
> 
> 
> On 2020/11/06 1:56, Mark Dilger wrote:
>>> On Nov 5, 2020, at 8:20 AM, Fujii Masao <masao.fujii@oss.nttdata.com> wrote:
>>> 
>>> The patch that makes pg_stat_statements track the number of rows that
>>> REFRESH MATERIALIZED VIEW command processes was proposed at [1].
>>> When reviewing the patch, I just wondered why the completion tag output
>>> for REFRESH MATERIALIZED VIEW doesn't include the row count. Is this
>>> an intentional behavior? I've not found the past discussion about this yet.
>> Of 191 command tags, only 7 return the number of rows.  See src/include/tcop/cmdtaglist.h.  REFRESH MATERIALIZED VIEW is similar to CREATE MATERIALIZED VIEW and also CREATE TABLE AS, which also do not return the row count.
> 
> Yes, so I was wondering if REFRESH MATERIALIZED VIEW also should use
> CMDTAG_SELECT like CREATE MATERIALIZED VIEW does.

For both CREATE MATERIALIZED VIEW and CREATE TABLE AS, ExecCreateTableAs() does:

  SetQueryCompletion(qc, CMDTAG_SELECT, queryDesc->estate->es_processed);

but ExecRefreshMatView() does nothing with it's QueryCompletion parameter.   I don't know why this case should behave differently than the other two.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company