Multi Inserts in CREATE TABLE AS - revived patch

Hi,

I would like to propose an updated patch on multi/bulk inserts in CTAS [1]
that tries to address the review comments that came up in [1]. One of the
main review comments was to calculate/estimate the tuple size to decide on
when to flush. I tried to solve this point with a new function
GetTupleSize()(see the patch for implementation).

I did some testing with custom configuration[2].

Use case 1- 100mn tuples, 2 integer columns, exec time in sec:
HEAD: *131.507* when the select part is not parallel, 128.832 when the
select part is parallel
Patch: 98.925 when the select part is not parallel, *52.901* when the
select part is parallel

Use case 2- 10mn tuples, 4 integer and 6 text columns, exec time in sec:
HEAD: *76.801* when the select part is not parallel, 66.074 when the select
part is parallel
Patch: 74.083 when the select part is not parallel, *57.739* when the
select part is parallel

Thoughts?

If the approach followed in the patch looks okay, I can work on a separate
patch for multi inserts in refresh materialized view cases.

I thank Simon Riggs for the offlist discussion.

PS: I chose to start a new thread as the previous thread [1] was closed in
the CF. I hope that's not a problem.

[1] -
https://www.postgresql.org/message-id/CAEET0ZHRWxbRUgwzUK_tOFDWx7VE2-P%3DxMBT6-N%2BgAa9WQ%3DxxA%40mail.gmail.com
[2] - The postgresql.conf used:
shared_buffers = 40GB
synchronous_commit = off
checkpoint_timeout = 1d
max_wal_size = 24GB
min_wal_size = 15GB
autovacuum = off

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com