From: Robert Klemme <shortcutter@googlemail.com>
To: pgsql-performance@postgresql.org
Subject: Re: Postgres for a "data warehouse", 5-10 TB
Date: Mon, 12 Sep 2011 19:15:35 +0200
Message-ID: <j4lens$hp0$1@dough.gmane.org> (raw)
In-Reply-To: <CABRT9RB-etP-K-0u0y-Wv+BysSd9ToZm71BqcY7hFQZC2tmjYQ@mail.gmail.com>
References: <CAMhtkAbK7saRO_Tayb1nS3YLWN=Wns=Ci47qs-3YbX0T2+hkpA@mail.gmail.com>
<CAOR=d=0zmw-EGRJyYmwCTxR5g6osbFLS5i-3kzjG05j7S=1JaA@mail.gmail.com>
<CAMhtkAah2c4XfSec=OtgL1V51wpD=jygbZnBVBRYCV02MscebQ@mail.gmail.com>
<4E6CC458.4010206@squeakycode.net>
<CABRT9RB-etP-K-0u0y-Wv+BysSd9ToZm71BqcY7hFQZC2tmjYQ@mail.gmail.com>
On 11.09.2011 19:02, Marti Raudsepp wrote:
> On Sun, Sep 11, 2011 at 17:23, Andy Colson<andy@squeakycode.net> wrote:
>> On 09/11/2011 08:59 AM, Igor Chudov wrote:
>>> By the way, does that INSERT UPDATE functionality or something like this exist in Postgres?
>> You have two options:
>> 1) write a function like:
>> create function doinsert(_id integer, _value text) returns void as
>> 2) use two sql statements:
>
> Unfortunately both of these options have caveats. Depending on your
> I/O speed, you might need to use multiple loader threads to saturate
> the write bandwidth.
>
> However, neither option is safe from race conditions. If you need to
> load data from multiple threads at the same time, they won't see each
> other's inserts (until commit) and thus cause unique violations. If
> you could somehow partition their operation by some key, so threads
> are guaranteed not to conflict each other, then that would be perfect.
> The 2nd option given by Andy is probably faster.
>
> You *could* code a race-condition-safe function, but that would be a
> no-go on a data warehouse, since each call needs a separate
> subtransaction which involves allocating a transaction ID.
Wouldn't it be sufficient to reverse order for race condition safety?
Pseudo code:
begin
insert ...
catch
update ...
if not found error
end
Speed is another matter though...
Kind regards
robert
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To: pgsql-performance@postgresql.org
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Subject: Re: Postgres for a "data warehouse", 5-10 TB
In-Reply-To: <j4lens$hp0$1@dough.gmane.org>
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