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https://issues.apache.org/jira/browse/DERBY-5367?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Kristian Waagan updated DERBY-5367:
-----------------------------------
Attachment: derby-5367-4a-fix_with_optimization_improved.diff
Attaching patch 4a, which takes another approach when it comes to optimizing
the code. The old/current code will be run on indexes which don't have collated
types, whereas the for indexes with collated types all fields will be updated
(one by one).
Hopefully, one should see identical performance in the normal case with this
patch.
With collated types performance will drop as indicated in the performance
results I posted above (worst case). It might be possible to trade CPU for IO,
i.e. to compare the values before deciding to update the field. One can also
avoid updating fields that aren't collated (only relevant for composite keys).
Patch ready for review.
> 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,
> derby-5367-3a-update_field_by_field_preview.diff,
> derby-5367-4a-fix_with_optimization_improved.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.
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