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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3571) LOB locators are not released if the LOB columns are not accessed by the client
Date Mon, 31 Mar 2008 21:30:24 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3571?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12583882#action_12583882
] 

Knut Anders Hatlen commented on DERBY-3571:
-------------------------------------------

All elements of SingleReleaseLOBTracker.trackColumn[] are false until checkCurrentRow() is
called (normally on ResultSet.next()). Doesn't this mean that the LOBs in the first row returned
from the query won't be released until the transaction is completed?

In SingleReleaseLOBTracker.checkCurrentRow(), should trackColumn[i] be set to true unconditionally
rather than in the else block? Whether or not column i were accessed in row n shouldn't affect
whether we release the locator in row n+1, should it?

Nit: SingleReleaseLOBTracker.noRelease() doesn't need the sanity check variable (indexFound)
if "break" is replaced with "return", and "ASSERT" is replaced with "THROWASSERT". Actually,
since columns[] is a sorted int array (isn't it?), it should be possible to simplify this
method further by using Arrays.binarySearch().

Typo in ResultSet.createLOBColumnTracker(): "simply" -> "simplify"

> 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,
derby-3571-1e-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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