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https://issues.apache.org/jira/browse/DERBY-1482?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali updated DERBY-1482:
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ReadExternal should never need to access anything about "soft/hard upgrade".
The state of the object is defined by whatever it is reading from disk. How to
build the object is all determined by the first int you read from disk.
After thinking about it I agree there should not be "soft/hard upgrade"
references in the writeExternal. Somehow the object itself should know whether
it should write the old or
new format out. I think you may be describing some tricky ways to do this. I
think if I were
doing this I would just add a new field to the object, something like
version_id. If version_id = 0 then write old format, if version_id=1 then
write new version. Read external will need to change to set this
appropriately. And the code that is called by create trigger will also need to
change to set this correctly based on database version, this probably is in the
constructor somewhere.
Do add more comments to the read and write external describing better the old
and new formats. What you are proposing is a little tricky, so best to have
some block of code that describes "version 0" format and "version 1" format.
If you get this right from bottom up then I think all the hard/soft upgrade
stuff will just work correctly. I would leave how you get the old format
converted to new format as a
last step, as you need to make sure old format in new db's yields correct
results (while maybe not optimized results).
> 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
> Attachments: derby1482_patch1_diff.txt, derby1482_patch1_stat.txt,
> derby1482_patch2_diff.txt, derby1482_patch2_stat.txt,
> derby1482DeepCopyAfterTriggerOnLobColumn.java, derby1482Repro.java,
> derby1482ReproVersion2.java, junitUpgradeTestFailureWithPatch1.out,
> TriggerTests_ver1_diff.txt, TriggerTests_ver1_stat.txt
>
>
> 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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