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From: Tom Lane <tgl@sss.pgh.pa.us>
To: ldh@laurent-hasson.com <ldh@laurent-hasson.com>
Cc: pgsql-performance@postgresql.org <pgsql-performance@postgresql.org>
Subject: Re: Zero throughput on a query on a very large table.
Date: Fri, 25 Jan 2019 15:04:37 -0500
Message-ID: <31319.1548446677@sss.pgh.pa.us> (raw)
In-Reply-To: <BN6PR15MB1185CC28C1DF4B94A6FAD2CC859B0@BN6PR15MB1185.namprd15.prod.outlook.com>
References: <BN6PR15MB1185DB9366CD57353DDD22C4859B0@BN6PR15MB1185.namprd15.prod.outlook.com>
	<29285.1548397485@sss.pgh.pa.us>
	<BN6PR15MB11858B89B18A47FAB8430A34859B0@BN6PR15MB1185.namprd15.prod.outlook.com>
	<2201.1548439855@sss.pgh.pa.us>
	<BN6PR15MB1185AA2A1C14BBF83AE9C69B859B0@BN6PR15MB1185.namprd15.prod.outlook.com>
	<3630.1548441241@sss.pgh.pa.us>
	<BN6PR15MB1185E4664C980E40D1450B06859B0@BN6PR15MB1185.namprd15.prod.outlook.com>
	<BN6PR15MB1185CC28C1DF4B94A6FAD2CC859B0@BN6PR15MB1185.namprd15.prod.outlook.com>

"ldh@laurent-hasson.com" <ldh@laurent-hasson.com> writes:
> Second, here is what i found and what messed us up.

>     select current_setting('random_page_cost'); --> 4
>     alter database "CMS_TMP" set random_page_cost=0.00000001;
>     select current_setting('random_page_cost'); --> 4 ????

ALTER DATABASE only affects subsequently-started sessions.

> I also tried:
>     select current_setting('random_page_cost'); --> 4
>     select set_config('random_page_cost', '0.000001', true);
>     select current_setting('random_page_cost'); --> 4 ????

That "true" means "local to the current transaction", which is
just the one statement if you don't have a BEGIN.

			regards, tom lane




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