Re: WIP: Avoid creation of the free space map for small tables

From: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
To: John Naylor <john(dot)naylor(at)2ndquadrant(dot)com>
Cc: Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: WIP: Avoid creation of the free space map for small tables
Date: 2019-01-29 10:55:52
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On Tue, Jan 29, 2019 at 5:59 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> On Tue, Jan 29, 2019 at 12:37 AM John Naylor
> <john(dot)naylor(at)2ndquadrant(dot)com> wrote:
> > > I think here you need to clear the map if it exists or clear it
> > > unconditionally, the earlier one would be better.
> >
> > Ok, maybe all callers should call it unconditonally, but within the
> > function, check "if (FSM_LOCAL_MAP_EXISTS)"?
> >
> Sounds sensible. I think we should try to reproduce these failures,
> for ex. for pgbench failure, we can try the same test with more
> clients.

I am able to reproduce this by changing pgbench test as below:

--- a/src/bin/pgbench/t/
+++ b/src/bin/pgbench/t/
@@ -56,9 +56,9 @@ $node->safe_psql('postgres',
'CREATE UNLOGGED TABLE insert_tbl (id serial primary key); ');

- '--no-vacuum --client=5 --protocol=prepared --transactions=25',
+ '--no-vacuum --client=10 --protocol=prepared --transactions=25',
- [qr{processed: 125/125}],
+ [qr{processed: 250/250}],

You can find this change in attached patch. Then, I ran the make
check in src/bin/pgbench multiple times using
You can vary the number of times the test should run, if you are not
able to reproduce it with this.

The attached patch (clear_local_map_if_exists_1.patch) atop the main
patch fixes the issue for me. Kindly verify the same.

With Regards,
Amit Kapila.

Attachment Content-Type Size
change_pgbench_test_1.patch application/octet-stream 607 bytes text/x-sh 49 bytes
clear_local_map_if_exists_1.patch application/octet-stream 1.4 KB

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