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https://issues.apache.org/jira/browse/DERBY-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030999#comment-13030999
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Mamta A. Satoor commented on DERBY-1482:
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I ran derbyall and junit suite with this patch and found that handful of
upgrade tests are failing. After debugging, I have found the reason to be that
my patch does optimization of reading only required columns and hence the
trigger action column positions in that selective list of read columns may not
be same as their column positions in this underlying trigger table. This column
mismatch is not recognized by 10,7 released jars. I am making changes that when
in soft upgrademode, do not do the column reading optimization so the generated
trigger action sql will still work when it is taken back to the older release
which does not do any column reading optimization.
> Update triggers on tables with blob columns stream blobs into memory even
> when the blobs are not referenced/accessed.
> ---------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-1482
> URL: https://issues.apache.org/jira/browse/DERBY-1482
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.2.1.6
> Reporter: Daniel John Debrunner
> Assignee: Mamta A. Satoor
> Priority: Minor
> Labels: LOB
> Fix For: 10.7.1.1
>
> Attachments: DERBY_1482_patch4_diff.txt, DERBY_1482_patch4_stat.txt,
> TriggerTests_ver1_diff.txt, TriggerTests_ver1_stat.txt,
> derby1482DeepCopyAfterTriggerOnLobColumn.java, derby1482Repro.java,
> derby1482ReproVersion2.java, derby1482_patch1_diff.txt,
> derby1482_patch1_stat.txt, derby1482_patch2_diff.txt,
> derby1482_patch2_stat.txt, derby1482_patch3_diff.txt,
> derby1482_patch3_stat.txt, junitUpgradeTestFailureWithPatch1.out
>
>
> Suppose I have 1) a table "t1" with blob data in it, and 2) an UPDATE trigger
> "tr1" defined on that table, where the triggered-SQL-action for "tr1" does
> NOT reference any of the blob columns in the table. [ Note that this is
> different from DERBY-438 because DERBY-438 deals with triggers that _do_
> reference the blob column(s), whereas this issue deals with triggers that do
> _not_ reference the blob columns--but I think they're related, so I'm
> creating this as subtask to 438 ]. In such a case, if the trigger is fired,
> the blob data will be streamed into memory and thus consume JVM heap, even
> though it (the blob data) is never actually referenced/accessed by the
> trigger statement.
> For example, suppose we have the following DDL:
> create table t1 (id int, status smallint, bl blob(2G));
> create table t2 (id int, updated int default 0);
> create trigger tr1 after update of status on t1 referencing new as n_row
> for each row mode db2sql update t2 set updated = updated + 1 where t2.id =
> n_row.id;
> Then if t1 and t2 both have data and we make a call to:
> update t1 set status = 3;
> the trigger tr1 will fire, which will cause the blob column in t1 to be
> streamed into memory for each row affected by the trigger. The result is
> that, if the blob data is large, we end up using a lot of JVM memory when we
> really shouldn't have to (at least, in _theory_ we shouldn't have to...).
> Ideally, Derby could figure out whether or not the blob column is referenced,
> and avoid streaming the lob into memory whenever possible (hence this is
> probably more of an "enhancement" request than a bug)...
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