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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-3571) LOB locators are not released if the LOB columns are not accessed by the client
Date Mon, 31 Mar 2008 11:04:24 GMT

     [ https://issues.apache.org/jira/browse/DERBY-3571?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kristian Waagan updated DERBY-3571:
-----------------------------------

    Attachment: derby-3571-1d-client_track_lob_fix.diff

'derby-3571-1d-client_track_lob_fix.diff' introduces a LOBStateTracker interface and two implementations
of it: SingleReleaseLOBTracker and NoOpLOBTracker. As a follow-up patch for DERBY-3575, I
plan to add MultipleReleaseLOBTracker.

The trackers will use different mechanisms to release the locators. A final step, which I
don't plan to implement for 10.4, is to piggy-back locators to release to the server on other
requests. This approach is why I chose to add the locatorsForRelease method.

To sum of the mechanism used by the trackers:
 * NoOpLOBTracker: no release
 * SingleReleaseLOBTracker: a stored procedure call for each locator to release, invoked at
every result set navigational methods and rs.close.
 * MultipleReleaseLOBTracker: a stored procedure call for a set of locators to release, invocation
time not yet decided.

I'm running tests, and if they pass I plan to commit this patch later today.

> LOB locators are not released if the LOB columns are not accessed by the client
> -------------------------------------------------------------------------------
>
>                 Key: DERBY-3571
>                 URL: https://issues.apache.org/jira/browse/DERBY-3571
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC, Network Client
>    Affects Versions: 10.3.2.1, 10.4.0.0, 10.5.0.0
>            Reporter: Kristian Waagan
>            Assignee: Kristian Waagan
>         Attachments: derby-3571-1a-client_track_lob_fix.diff, derby-3571-1a-client_track_lob_fix.stat,
derby-3571-1b-client_track_lob_fix.diff, derby-3571-1c-client_track_lob_fix.diff, derby-3571-1d-client_track_lob_fix.diff
>
>
> If the client creates a result set containing LOB locator columns and iterates through
it without actually accessing the LOB columns, the locators are not released.
> The amount of locators and their associated LOB objects causes the server to consume
large amounts of memory and it eventually gets an OOME.
> There are a few workarounds for this bug:
>  a) Access and/or properly close the LOBs (i.e. Blob.free).
>     This is partly dependent on DERBY-2892.
>  b) Invoke Connection.commit (or rollback) periodically, which causes all locators on
the connection to be released.

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