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http://issues.apache.org/jira/browse/DERBY-1876?page=comments#action_12436700 ]
Daniel John Debrunner commented on DERBY-1876:
----------------------------------------------
JDBC requires that each execution of ps.executeQuery() returns a new ResultSet
object, thus looking at the code within EmbedResultSet() constructor is worth
while.
There are at least four sub-optimal pieces of code:
1) (long)stmt.getQueryTimeout() * 1000L;
Each creation a multiplication by 1000 is executed, could be avoided by
having the
value in ms calculated once and stored in EmbedStatement when
setQueryTimeout is called.
2) stmt.getResultSetConcurrency()
This call checks the Statement object to see if it is open, but it must be
open since it is creating a ResultSet. Can be avoided by having EmbedResultSet
use the final field that holds the concurrency, if iw was made package
protected.
3) final int columnCount = getMetaData().getColumnCount();
This creates a ResultSetMetaData object that will not be used in the
typical case (at least I think it will not be used). Using
resultDescription.getColumnCount() would get the count with no object creation.
4) this.currentRow = factory.getValueRow(columnCount);
currentRow.setRowArray(null);
The call to getValueRow() creates a ValueRow with a new DataValueDescriptor
array within it, the next line nulls out the refrence to the array. Thus this
creates a short lived object for no value. Possibly work around is to have
currentRow use the array directly, or create a ValueRow with no array within it.
> Investigate overhead of JDBC layer and compiled activation code for simple
> embedded read-only, forward ResultSets
> -----------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-1876
> URL: http://issues.apache.org/jira/browse/DERBY-1876
> Project: Derby
> Issue Type: Improvement
> Components: JDBC, Performance
> Reporter: Daniel John Debrunner
> Priority: Minor
> Attachments: derby1876.java
>
>
> For simple ResultSet usage like:
> ResultSet rs = ps.executeQuery();
> while (rs.next()) {
> rs.getInt(1);
> rs.getInt(2);
> rs.getInt(3);
> }
> rs.close();
> it would be interesting to see how much overhead could be removed with simple
> changes, or possibly removed if there was a simple ResultSet implementation
> for forward only, read-only ResultSet, and the more complete implementation
> for all other ResultSet types such as updateable and/or scrollable. Has
> introducing updateable ResultSets, for example, degraded the performance of
> read-only ResultSets? Could code be changed so that a typical read-only
> Resultset is not affected by the code required for richer ResultSets?
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