Extend Sequoia controller to handle differences in backend driver handling of
setFetchSize() hints
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Key: SEQUOIA-1001
URL: https://forge.continuent.org/jira/browse/SEQUOIA-1001
Project: Sequoia
Type: New Feature
Versions: Sequoia 2.10.9
Environment: All
Reporter: Robert Hodges
Fix For: sequoia 2.10.10
JDBC setFetchSize() calls allow users to request that results be streamed back
from backends into clients. Sequoia handles setFetchSize calls (for example
Statement.setFetchSize() consistently, but underlying drivers may reject hints,
which means that the result set, however large, is just streamed into memory.
This is a problem because it is necessary to fetch subsets of rows for large
result sets. Testing with Bristlecone shows that even result sets of 100K
rows quickly cause the controller to run out of Java heap space.
For example MySQL Connector/J only accepts Integer.MIN_VALUE as a fetch size
hint and ignores all other settings (i.e., they are the same as 0). Other JDBC
drivers may have similar behavior. This is a problem because Sequoia generally
follows the JDBC specification, so we need the ability to map fetch size values
to what ever wierdness the driver accepts.
This feature extends the Sequoia ControllerFactory to add a
DriverComplianceFactory. The factory in turn returns DriverCompliance
instances, thereby making it possible to extend them. Finally, the
DriverCompliance class has a new method DriverCompliance.convertFetchSize()
which converts requested fetch values to a reasonable value for the underlying
driver. The default implementation simply hands back the requested value but
other implementations can perform different conversions if desired.
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