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The Basics
Id: 109244
Status: rejected
Priority: 0/
Queue: DBD-Pg

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Owner: Nobody in particular
Requestors: skaurus [...] gmail.com
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Severity: (no value)
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Fixed in: (no value)



Subject: BEGIN READ ONLY
Date: Fri, 20 Nov 2015 21:41:12 +0300
To: bug-DBD-Pg [...] rt.cpan.org
From: Дмитрий Шалашов <skaurus [...] gmail.com>
Hi, could you expose BEGIN READ ONLY functionality? Why do we need this. We have following setup: * PostgreSQL 9.4 master + slave * pgpool-II 3.4.3 as connection pooler and load balancer * pgpool set up in a way that almost all read queries are balanced to slave. Problem lies within pgpool detection whether query writes or not (former ones can't be routed to slave). This query routes to slave: BEGIN; SELECT pg_sleep(15); -- pg_sleep used so it is easy to check where query is running COMMIT; But this query routes to master: BEGIN; SET TRANSACTION TO READ ONLY; -- we need this to don't grow XIDs on readonly queries SELECT pg_sleep(15); COMMIT; And this query routes correctly (to slave) again: BEGIN READ ONLY; SELECT pg_sleep(15); COMMIT; I hesitate calling DB directly like this: $dbh->do('BEGIN READ ONLY'); $dbh->do('SELECT pg_sleep(15)); $dbh->do('COMMIT'); because DBD::Pg have a lot going under its hood and I feel kinda insecure missing all this. Maybe I'm wrong here? Dmitry Shalashov, surfingbird.ru & relap.io
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> I hesitate calling DB directly like this: > $dbh->do('BEGIN READ ONLY'); > $dbh->do('SELECT pg_sleep(15)); > $dbh->do('COMMIT'); > because DBD::Pg have a lot going under its hood and I feel kinda insecure > missing all this. Maybe I'm wrong here?
I think you should be fine using do() like that. It is difficult to see how we would extend $dbh->begin_work() anyway, as it's a DBI method.
Subject: Re: [rt.cpan.org #109244] BEGIN READ ONLY
Date: Mon, 3 Apr 2017 13:02:47 +0300
To: bug-DBD-Pg [...] rt.cpan.org
From: Dmitry Shalashov <skaurus [...] gmail.com>
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Thanks, Greg! Dmitry Shalashov, surfingbird.ru & relap.io 2017-04-03 5:17 GMT+03:00 Greg Sabino Mullane via RT <bug-DBD-Pg@rt.cpan.org Show quoted text
>:
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> <URL: https://rt.cpan.org/Ticket/Display.html?id=109244 > > >
> > I hesitate calling DB directly like this: > > $dbh->do('BEGIN READ ONLY'); > > $dbh->do('SELECT pg_sleep(15)); > > $dbh->do('COMMIT'); > > because DBD::Pg have a lot going under its hood and I feel kinda insecure > > missing all this. Maybe I'm wrong here?
> > I think you should be fine using do() like that. It is difficult to see > how we would extend $dbh->begin_work() anyway, as it's a DBI method. > > > >


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