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https://issues.apache.org/jira/browse/DERBY-3354?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12563539#action_12563539
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Knut Anders Hatlen commented on DERBY-3354:
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> I believe this is because EmbedConnection.addLobMapping is called for every
> lob creation but is never cleared until commit or rollback, even if the lob
> is freed.
I believe your analysis is correct. free() should remove the mapping.
Unfortunately, the lob doesn't know about its locator value, but it seems like
your about to change that by adding a getLocator() method in DERBY-3243.
On DERBY-3243 I wrote:
> Another thing I came to think about: Would it be better to remove
> addLOBMapping() from the constructors in EmbedBlob/EmbedClob and instead call
> it lazily from getLocator()? (...) Then we'd also remove the overhead of
> maintaining the lob mapping in embedded mode.
I think that change would fix the OOME (on embedded, but we'd probably still
see it in a client/server environment).
Now, it seems like DERBY-2787 added the call to addLOBMapping() intentionally
to ensure that free() was called on commit/rollback and temporary files would
be deleted. Moving addLOBMapping() out of the constructors would probably
reintroduce the problem with temporary files not being deleted. However, the
lobs only create temporary files when they are modified and the new size of the
lob is greater than the buffer in LOBStreamControl, so it shouldn't be
necessary to have commit/rollback call free() on all lobs to delete the
temporary files. It would probably be enough if each lob added itself to a list
in the connection each time a temporary file was created in
LOBStreamControl.init(). (addLOBMapping() is probably OK, but it feels a bit
strange to piggyback on a locator mechanism to do this cleanup when we don't
actually care about the locators.)
> Select from large lob table with embedded gives OutOfMemoryError
> ----------------------------------------------------------------
>
> Key: DERBY-3354
> URL: https://issues.apache.org/jira/browse/DERBY-3354
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Reporter: Kathey Marsden
> Attachments: LocLeak.java
>
>
> Retrieving from a large table with lobs gives an OutOfMemoryException, even
> if free() is explictly called on the lob. I believe this is because
> EmbedConnection.addLobMapping is called for every lob creation but is never
> cleared until commit or rollback, even if the lob is freed.
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