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Date: Wed, 08 Aug 2018 11:02:01 +0300
From: Marina Polyakova <m.polyakova@postgrespro.ru>
To: Fabien COELHO <coelho@cri.ensmp.fr>
Cc: pgsql-hackers@postgresql.org, Alvaro Herrera <alvherre@2ndquadrant.com>,
 Ildus Kurbangaliev <i.kurbangaliev@postgrespro.ru>, Teodor Sigaev
 <teodor@sigaev.ru>
Subject: Re: [HACKERS] WIP Patch: Pgbench Serialization and deadlock errors
Organization: Postgres Professional
In-Reply-To: <alpine.DEB.2.21.1808071814380.13466@lancre>
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On 07-08-2018 19:21, Fabien COELHO wrote:
> Hello Marina,

Hello, Fabien!

>> v10-0001-Pgbench-errors-use-the-RandomState-structure-for.patch
>> - a patch for the RandomState structure (this is used to reset a 
>> client's random seed during the repeating of transactions after 
>> serialization/deadlock failures).
> 
> About this v10 part 1:
> 
> Patch applies cleanly, compile, global & local make check both ok.
> 
> The random state is cleanly separated so that it will be easy to reset
> it on client error handling ISTM that the pgbench side is
> deterministic with
> the separation of the seeds for different uses.
> 
> Code is clean, comments are clear.

:-)

> I'm wondering what is the rational for the "xseed" field name? In
> particular, what does the "x" stands for?

I called it "...seed" instead of "data" because perhaps the "data" is 
too general a name for use here (but I'm not entirely sure what Alvaro 
Herrera meant in [1], see my answer in [2]). I called it "xseed" to 
combine it with the arguments of the functions _dorand48 / pg_erand48 / 
pg_jrand48 in the file erand48.c. IIUC they use a linear congruential 
generator and perhaps "xseed" means the sequence with the name X of 
pseudorandom values of size 48 bits (X_0, X_1, ... X_n) where X_0 is the 
seed / the start value.

[1] 
https://www.postgresql.org/message-id/20180711180417.3ytmmwmonsr5lra7@alvherre.pgsql

> LGTM, though I'd rename the random_state struct members so that it
> wouldn't look as confusing.  Maybe that's just me.

[2] 
https://www.postgresql.org/message-id/cb2cde10e4e7a10a38b48e9cae8fbd28%40postgrespro.ru

-- 
Marina Polyakova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company