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Re: Help with bulk read performance

From: "Pierre C" <lists(at)peufeu(dot)com>
To: "Andy Colson" <andy(at)squeakycode(dot)net>, "Dan Schaffer" <Daniel(dot)S(dot)Schaffer(at)noaa(dot)gov>
Cc: "Jim Nasby" <jim(at)nasby(dot)net>, pgsql-performance(at)postgresql(dot)org, "Nick Matheson" <Nick(dot)D(dot)Matheson(at)noaa(dot)gov>
Subject: Re: Help with bulk read performance
Date: 2010-12-16 15:22:40
Message-ID: op.vntbn2ujeorkce@apollo13 (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
> If the data are stored as a byte array but retrieve into a ResultSet,  
> the unpacking time goes up by an order of magnitude and the
> observed total throughput is 25 MB/s.  If the data are stored in a  
> Postgres float array and unpacked into a byte stream, the
> observed throughput is 20 MB/s.

float <-> text conversions are very slow, this is in fact due to the  
mismatch between base-2 (IEEE754) and base-10 (text) floating point  
representation, which needs very very complex calculations.

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