Re: incorrect docs for pgbench / skipped transactions

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
Cc: PostgreSQL Developers <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: incorrect docs for pgbench / skipped transactions
Date: 2016-03-19 07:29:15
Message-ID: alpine.DEB.2.10.1603190805170.7678@sto
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Hello Tomas,

> while learning about format of the transaction log produced by pgbench, I've
> noticed this sentence in the section describing format of the per-transaction
> log:
>
> The last field skipped_transactions reports the number of
> transactions skipped because they were too far behind schedule.
> It is only present when both options --rate and --latency-limit
> are used.
>
> Which is wrong, because this field is only added in the aggregated log, not
> in the per-transaction one. So we should delete this.

Indeed.

Several builtin scripts can be specified with -b as well, and -b and -f
can be mixed, the file_no should be renamed script_no and refer to both -b
and -f.

> It also does not explicitly explain that with --latency-limit the latency
> column will contain "skipped" for transactions exceeding the limit latency
> (it's only mentioned in the example output).

Ok.

> So I think we should apply the attached patch (and also backpatch it to 9.5,
> where the --latency-limit got introduced).

Here is an updated version of your proposal:
- use <literal> instead of "
- use script_no and mention -b as well
- spell out skipped explanation after the sample output

Also, while reading the doc, I really think that the timestamp should be
made explicit milliseconds, i.e. "123.004567" instead of "123 4567", but
that is another question not relevant to this patch.

--
Fabien.

Attachment Content-Type Size
pgbench-skipped-doc-fix-2.patch text/x-diff 2.3 KB

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