Fetch size hints result in null pointer exception for autocommit reads
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Key: SEQUOIA-1003
URL: https://forge.continuent.org/jira/browse/SEQUOIA-1003
Project: Sequoia
Type: Bug
Versions: Sequoia 2.9
Environment: All, confirmed using MySQL.
Reporter: Robert Hodges
Assigned to: Robert Hodges
Fix For: sequoia 2.10.10
Sequoia set fetch size processing does not work properly for autocommit reads.
The problem is that when using set fetch size you must hold onto the
connection until all results have been read out. However, the current
behavior of Sequoia is that for autocommit requests the connection is freed
after doing a select. This means that either the connection will be logged
out or reused if it takes a while to fetch back results.
To illustrate the problem approximately, ensure the VDB has a table with at
least 10 rows. Login using the console and enter the following commands:
> fetchsize 5
> select * from yourtable
The console will ask you to press enter to see more results. Go away for a
few minutes before presssing enter so that the connection pool will drop or
reuse the connection. You should now get a null pointer exception.
For an example of misbehaving code, see RAIDb1.executeRequestOnBackend(), which
invokes code to run a select then immediately gives up the connection:
rs = executeStatementExecuteQueryOnBackend(request, backend, null, c
.getConnection(), metadataCache);
cm.releaseConnectionInAutoCommit(request, c);
The fix for this problem is to cache the connection in the ControllerResult set
and release it when finished reading the underlying result set.
NOTE: There is no problem when running reads within transactions. In this
case the connection will be held until there is a commit or rollback statement.
Unfortunately this problem is quite serious for native applications
especially once it is possible to set the fetch size using a connection
property.
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