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Message-ID: <468D57F3.7030405@Yahoo.com>
Date: Thu, 05 Jul 2007 16:43:31 -0400
From: Jan Wieck <JanWieck@Yahoo.com>
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To: Tom Lane <tgl@sss.pgh.pa.us>
CC: PostgreSQL Development <pgsql-hackers@postgresql.org>
Subject: Re: usleep feature for pgbench
References: <468D42B3.4010701@Yahoo.com> <20905.1183664046@sss.pgh.pa.us>
In-Reply-To: <20905.1183664046@sss.pgh.pa.us>
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On 7/5/2007 3:34 PM, Tom Lane wrote:
> Jan Wieck <JanWieck@Yahoo.com> writes:
>> To test some changes in Slony I needed a
>>      \usleep [microseconds|:variable]
>> in pgbench's scripting language to be able to have hundreds of 
>> concurrent running transactions without totally swamping the system. I 
>> was wondering if anyone would object to permanently adding this to the 
>> pgbench code?
> 
> How's it implemented?  Does the whole pgbench app freeze up for the
> duration of the sleep, or does it just delay that one client script?

Only that one client script.

The \usleep command itself calculates a "struct timeval until" that sits 
in the state struct and sets a "sleeping" flag also in the state struct. 
  So both are per client script/connection and multiple clients can be 
sleeping in an overlapping fashion. The loop in main() then picks the 
lowest timeval (if there is anyone sleeping) and uses that to calculate 
the timeout for select(). doCustom() resets the sleeping flag for those 
scheduled for wakeup and advances the client to the next scripted command.

I think I've coded it in a way that if one doesn't use the \usleep 
command at all, it will never even call gettimeofday() and use a NULL 
timeout in select() as it used to.


Jan

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