Re: [PROPOSAL] VACUUM Progress Checker.

From: Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
To: vinpokale(at)gmail(dot)com
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: [PROPOSAL] VACUUM Progress Checker.
Date: 2015-12-01 07:25:57
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At Mon, 30 Nov 2015 19:10:44 -0700 (MST), Vinayak <vinpokale(at)gmail(dot)com> wrote in <1448935844520-5875614(dot)post(at)n5(dot)nabble(dot)com>
> Thanks for the v7.
> Please check the comment below.
> -Table name in the vacuum progress
> + snprintf(progress_message[0], PROGRESS_MESSAGE_LENGTH, "%s.%s",
> schemaname,relname);
> In the vacuum progress, column table_name is showing first 30 characters of
> table name.

Yeah, it is actually restricted in that length. But if we allow
the buffer to store whole the qualified names, it will need 64 *
2 + 1 +1 = 130 bytes * 10 1300 bytes for each beentry... It might
be acceptable by others, but I don't think that is preferable..

Separating namespace and relation name as below reduces the
required length of the field but 62 bytes is still too long for
most of the information and in turn too short for longer messages
in some cases.

As a more dractic change in design, since these fields are
written/read in sequential manner, providing one free buffer of
the size of.. so.. about 128 bytes for each beentry and storing
strings delimiting with '\0' and numbers in binary format, as an
example, would do. Additional functions to write into/read from
this buffer safely would be needed but this gives both the
ability to store longer messages and relatively short total
buffer size, and allows arbitrary number of parameters limited
only by the length of the free buffer.

What do you think about this?

By the way, how about giving separate columns for relname and
namespace? I think it is more usual way to designate a relation
in this kind of view and it makes the snprintf to concatenate
name and schema unnecessary(it's not significant, though). (The
following example is after pg_stat_all_tables)

> postgres=# create table test_vacuum_progress_in_postgresql(c1 int,c2 text);
> postgres=# select * from pg_stat_vacuum_progress ;
> pid | 12284
> schemaname | public
> relname | test_vacuum_progress_i...
> phase | Scanning Heap
> total_heap_pages | 41667

And I have some comments about code.


Kyotaro Horiguchi
NTT Open Source Software Center

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