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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Closed: (DERBY-3882) Expensive cursor name lookup in network server
Date Fri, 25 Sep 2009 10:10:16 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3882?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Knut Anders Hatlen closed DERBY-3882.
-------------------------------------

          Resolution: Fixed
       Fix Version/s: 10.6.0.0
    Issue & fix info:   (was: [Patch Available])

Committed revision 818807.

> Expensive cursor name lookup in network server
> ----------------------------------------------
>
>                 Key: DERBY-3882
>                 URL: https://issues.apache.org/jira/browse/DERBY-3882
>             Project: Derby
>          Issue Type: Improvement
>          Components: Network Server, SQL
>    Affects Versions: 10.4.2.0
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>            Priority: Minor
>             Fix For: 10.6.0.0
>
>         Attachments: check_hash.diff, Cursors.java
>
>
> 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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