2011-07-16Planning with Actual Bind Values
PostgreSQL does not have a shared query plan cache, but it has an optional query plan cache for prepared statements. That means that the developer has the choice to use a prepared statement with or without cached query plan. But note that the cache is dropped when the prepared statement is closed.
The following samples show how to use this functionality in various languages.
- C
The native C API provides the function
PQexecParams, which allows to use bind parameters during prepare (as opposed toPQprepare).- Java
The PostgreSQL JDBC driver controls server-side prepare via the non-standard method
setPrepareThresholdon PGStatement and PGConnection.Note that the default setting is five, which means that the first four executions will actually use the bind parameters during prepare, the later ones not. That counter starts fresh for each
PreparedStatementinstance.Warning
There are many frameworks that use a
PreparedStatementcache—configured viaprepared-statement-cache-sizein the data source setup. That means you can hit limit at any time.- Ruby
Ruby’s PGconn.exec accepts bind parameters as optional argument. The values will be used during planning if provided. Jeff Davis has an example.
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