db-derby-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] [Issue Comment Edited] (DERBY-1482) Update triggers on tables with blob columns stream blobs into memory even when the blobs are not referenced/accessed.
Date Tue, 10 May 2011 04:47:03 GMT

    [ https://issues.apache.org/jira/browse/DERBY-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13030999#comment-13030999
] 

Mamta A. Satoor edited comment on DERBY-1482 at 5/10/11 4:47 AM:
-----------------------------------------------------------------

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 the underlying trigger table.
This column mismatch is not recognized by 10.7 released jars. I am making changes that when
in soft upgrade mode, 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.

      was (Author: mamtas):
    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)... 

--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira

Mime
View raw message