[
https://issues.apache.org/jira/browse/DERBY-5367?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13100756#comment-13100756
]
Mike Matrigali commented on DERBY-5367:
---------------------------------------
For benchmarks it seems like we would like to know results for 2 different
types of benchmarks. The worst case for this code would be primary key insert
and delete repeated using the same key. I think that is what you are doing.
Then also just a normal mix of insert/delete. The question I would be trying
to understand is it worth the overhead to the "normal" path to know if we can
then optimize for the worst case path. Basically 3.6% degredation for that
worst case which I don't think is a normal usage pattern may be ok. What I
don't want to see is
slowdown is "normal" case which I think we might have seen with patch 1 that
did work in normal path to optimize the worst case path.
I think option 2 is a reasonable approach for a bug fix to existing codelines.
Seems safe to me, and a good first step. And doing it not
special cased gets us full testing that caught the previous problem with the
patch.
With more thought I don't think we should do option 1. I think it might make
sense to log a future project for the trunk to look into just going ahead a
purging the deleted row and then retrying the insert. Whie we have the latch
we may just want to purge all committed deleted rows
in a similar fashion to what we do previous to splitting the page.
The problem is that purge is tricky in that it has to be committed while
holding the latch on the page, you can't just call it in-line in the current
code. And you have to make sure that if you fork a transaction that parent is
not conflicting with child to do the purge, otherwise might loop
forever. The purge will also address the RESOLVE in the code right now (since
that comment was written HeapRowLocations are now variable in size based on
CompressedNumber) . And with the specific issue that is causing this issue it
is also
possible that updating "equal" fields might need more space given that
different characters and chacter sequences can be "equal". So the
problem is even possibly worse for the collation problem.
> Stale data retrieved when using new collation=TERRITORY_BASED:PRIMARY feature
> -----------------------------------------------------------------------------
>
> Key: DERBY-5367
> URL: https://issues.apache.org/jira/browse/DERBY-5367
> Project: Derby
> Issue Type: Bug
> Components: Store
> Affects Versions: 10.8.1.2, 10.9.0.0
> Environment: Mac OS X, Windows
> Reporter: Brett Wooldridge
> Assignee: Kristian Waagan
> Priority: Critical
> Attachments: derby-5367-1a-update_row_fully.diff,
> derby-5367-1b-update_row_fully.diff, derby-5367-1b-update_row_fully.stat,
> derby-5367-2a-minimal_fix.diff
>
>
> Our product recently upgraded to version 10.8.1.2 in order to take advantage
> of the new 'case-insensitive' mode offered by Derby in the form of the
> "collation=TERRITORY_BASED:PRIMARY" connection parameter.
> Unfortunately, we have run into an issue whereby stale data appears to be
> retrieved from an index, even though the data in the table itself has changed.
> You can see this issue in the IJ session below. The database in question was
> created using this Java parameter when invoking IJ:
> -Dij.database=jdbc:derby:test;create=true;collation=TERRITORY_BASED:PRIMARY
> Here is the IJ session:
> CONNECTION0* - jdbc:derby:test
> * = current connection
> ij> CREATE TABLE tag (
> tag_id INTEGER GENERATED BY DEFAULT AS IDENTITY NOT NULL,
> tag VARCHAR(255) NOT NULL,
> CONSTRAINT tag_pk PRIMARY KEY (tag_id),
> CONSTRAINT tag_tag_unique UNIQUE (tag)
> );
> 0 rows inserted/updated/deleted
> ij> -- first insert a value 'Test', note the upper-case 'T' in 'Test'
> ij> INSERT INTO tag (tag) VALUES ('Test');
> 1 row inserted/updated/deleted
> ij> SELECT * FROM tag;
> TAG_ID |TAG
>
> --------------------------------------------------------------------------------------------------------------------------------------------
> 1 |Test
>
> 1 row selected
> ij> -- Now delete the row
> ij> DELETE FROM tag WHERE tag='Test';
> 1 row inserted/updated/deleted
> ij> -- You could run another SELECT here to verify it is gone, but it is.
> ij> -- Now insert a new value 'test', note the lower-case 't' in 'test'
> ij> INSERT INTO tag (tag) VALUES ('test');
> 1 row inserted/updated/deleted
> ij> -- Now verify that the table contains only the lower-case version: 'test'
> ij> SELECT * FROM tag;
> TAG_ID |TAG
>
> --------------------------------------------------------------------------------------------------------------------------------------------
> 2 |test
>
> 1 row selected
> ij> -- Now, here is the bug.
> ij> SELECT tag FROM tag;
> TAG
>
> --------------------------------------------------------------------------------------------------------------------------------
> Test
>
> 1 row selected
> ij>
> Note in the last SELECT we specify the 'tag' column specifically. When we
> 'SELECT *', Derby performs a table-scan and the result is correct. However,
> when we 'SELECT tag', Derby appears to use the index created for the
> 'tag_tag_unique' unique constraint. As an optimization Derby, like many
> databases, will use values directly from the index in the case where the
> index covers all requested columns.
> The bigger question is, why doesn't the DELETE action cause the entry in the
> tag_tag_unique index to be deleted? Is this a further optimization? If so,
> it is imperative that the index at least be updated when the new value is
> inserted.
> This is rather a severe bug for us that causes stale data to be returned.
--
This message is automatically generated by JIRA.
For more information on JIRA, see: http://www.atlassian.com/software/jira
