Message-ID: <1115268106.4279a40a7481a@webmail.telus.net>
Date: Wed,  4 May 2005 21:41:46 -0700
From: Mischa Sandberg <mischa.sandberg@telus.net>
To: pgsql-performance@postgresql.org
Subject: Re: COPY vs INSERT
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Quoting Kris Jurka <books@ejurka.com>: 
 
> On Wed, 4 May 2005, Mischa Sandberg wrote: 
>  
> > Copy makes better use of the TCP connection for transmission. COPY 
> uses 
> > the TCP connection like a one-way pipe. INSERT is like an RPC: the 
> > sender has to wait until the insert's return status roundtrips. 
>  
> Not true.  A client may send any number of Bind/Execute messages on 
a 
> prepared statement before a Sync message.  So multiple inserts may 
be 
> sent  
> in one network roundtrip.  This is exactly how the JDBC driver  
> implements batch statements.  There is some limit to the number of 
> queries  
> in flight at any given moment because there is the potential to 
> deadlock  
> if both sides of network buffers are filled up and each side is 
> blocked  
> waiting on a write.  The JDBC driver has conservatively selected 256 
> as  
> the maximum number of queries to send at once. 
 
Hunh. Interesting optimization in the JDBC driver. I gather it is 
sending a string of (;)-separated inserts. Sounds like 
efficient-but-risky stuff we did for ODBC drivers at Simba ... gets 
interesting when one of the insert statements in the middle fails. 
Good to know. Hope that the batch size is parametric, given that you 
can have inserts with rather large strings bound to 'text' columns in 
PG --- harder to identify BLOBs when talking to PG, than when talking 
to MSSQL/Oracle/Sybase. 
 
-- 
Engineers think equations approximate reality. 
Physicists think reality approximates the equations. 
Mathematicians never make the connection.