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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-3882) Expensive cursor name lookup in network server
Date Thu, 25 Sep 2008 20:09:46 GMT
Expensive cursor name lookup in network server
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                 Key: DERBY-3882
                 URL: https://issues.apache.org/jira/browse/DERBY-3882
             Project: Derby
          Issue Type: Improvement
          Components: Network Server, Performance, SQL
    Affects Versions: 10.4.2.0
            Reporter: Knut Anders Hatlen
            Priority: Minor


I have sometimes seen in a profiler that an unreasonably high amount of the CPU time is spent
in GenericLanguageConnectionContext.lookupCursorActivation() when the network server is running.
That method is used to check that there is no active statement in the current transaction
with the same cursor name as the statement currently being executed, and it is normally only
used if the executing statement has a cursor name. None of the client-side statements had
a cursor name when I saw this.

The method is always called when the network server executes a statement because the network
server assigns a cursor name to each statement even if no cursor name has been set on the
client side. If the list of open statements is short, the method is relatively cheap. If one
uses ClientConnectionPoolDataSource with the JDBC statement cache, the list of open statements
can however be quite long, and lookupCursorActivation() needs to spend a fair amount of time
iterating over the list and comparing strings.

The time spent looking for duplicate names in lookupCursorActivation() is actually wasted
time when it is called from the network server, since the network server assigns unique names
to the statements it executes, even when there are duplicate names on the client. It would
be good if we could reduce the cost of this operation, or perhaps eliminate it completely
when the client doesn't use cursor names.

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