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https://issues.apache.org/jira/browse/DERBY-6300?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Mike Matrigali resolved DERBY-6300.
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Resolution: Unresolved
While not optimal the behavior described in DERBY-6300 is expected behavior.
Some plans chosen by the optimizer will result in row qualification above
store, and under some isolation levels in those cases locks on rows that do not
qualify may be kept until end of transaction. 2 other JIRA's improvement
requests have been filed driven by this issue and work will take place under
those issues. Those issues are DERBY-6301 and DERBY-6784.
User agreed that this issue could be resolved and that their requirements were
covered in the other JIRA's.
> row locks incorrectly taken for rows that do not match SELECT predicate
> -----------------------------------------------------------------------
>
> Key: DERBY-6300
> URL: https://issues.apache.org/jira/browse/DERBY-6300
> Project: Derby
> Issue Type: Bug
> Components: SQL, Store
> Affects Versions: 10.8.3.0, 10.10.1.1
> Environment: Windows, Linux
> Reporter: H Zhang
> Attachments: RowLocksIssue.java, derby.log
>
>
> Derby seems to be taking S-locks on all the rows in a table after a SELECT
> query, even when none of the rows match the query predicate. For example,
> after running a query like
> SELECT col1, col2 FROM table1 WHERE col1 IN (?, ?, ?...) WITH RS
> and the query returns 0 rows, we still see S-locks being taken on all rows in
> the table.
> This issue seems to be dependent on which exact query plan gets chosen to be
> executed, as changing some combination of the following factors seems to
> avoid the issue:
> 1) The number of total rows in the table is small. In the test case, we're
> using 10 rows.
> 2) There is an explicitly created composite index on the table that covers
> all the rows.
> 3) The number of values in the IN clause of the SELECT query is sufficiently
> large.
> What plan the optimizer chooses seems to be a factor. For example, in our
> actual database, we've found we need about 5 or 6 parameters in the IN clause
> to reproduce the issue. In the attached test case, it seems the issue can be
> seen with 3 or more parameters.
> The attached test results in a database deadlock if the row locking issue
> occurs. It basically does the following:
> a) Have a table with 10 rows. The values are basically A0, A1, ...
> b) Have a transaction selecting for values C0, C1, ...
> c) Have a 2nd transaction selecting for values D0, D1, ...
> d) Execute SQL deletes from both transactions
> The test fails in (d) with a deadlock because after (b) and (c), both
> transactions have S-locks on all the rows in the table.
> We've tested on 10.8.3 and 10.10.1.1, and both seem to exhibit the issue.
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