From: Ron Mayer <rm_pg@cheapcomplexdevices.com>
Subject: Multiple insert performance trick or performance misunderstanding?
Date: Sat, 24 Sep 2005 13:51:16 -0700
Organization: Hub.Org Networking Services
Lines: 32
Message-ID: <dh4e88$25qe$1@news.hub.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
User-Agent: Mozilla Thunderbird 1.0 (Windows/20041206)
To: pgsql-performance@postgresql.org

When I need to insert a few hundred or thousand things in
a table from a 3-tier application, it seems I'm much better
off creating a big string of semicolon separated insert
statements rather than sending them one at a time - even
when I use the obvious things like wrapping the statements
in a transaction and using the library's prepared statements.


I tried both Ruby/DBI and C#/Npgsql; and in both cases
sets of inserts that took 3 seconds when run individually
took about 0.7 seconds when concatenated together.

Is it expected that I'd be better off sending big
concatenated strings like
   "insert into tbl (c1,c2) values (v1,v2);insert into tbl (c1,c2) values (v3,v4);..."
instead of sending them one at a time?


db.ExecuteSQL("BEGIN");
sql = new System.Text.StringBulder(10000);
for ([a lot of data elements]) {
   sql.Append(
      "insert into user_point_features (col1,col2)"+
      " values ("                      +obj.val1 +","+obj.val2+");"
   );
}
db.ExecuteSQL(sql.ToString());
db.ExecuteSQL("COMMIT");