Avoid unnecessary use of getStream and getStreamWithDescriptor
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Key: DERBY-4563
URL: https://issues.apache.org/jira/browse/DERBY-4563
Project: Derby
Issue Type: Improvement
Components: JDBC
Affects Versions: 10.6.0.0
Reporter: Kristian Waagan
Assignee: Kristian Waagan
Priority: Minor
Fix For: 10.6.0.0
A pattern in Derby is to use the following piece of code to determine if the
data value has a stream or not:
if (dvd.getStream() != null) ...
Since the stream has mutable state, obtaining a reference to it just to check
if it is not null is sub-optimal for several reasons:
- it may throw an exception (data types not supporting streams)
- the stream reference is leaked, which is unfortunately if we are / will be
required to guarantee something about the stream state (for instance that the
descriptor is in sync with the stream).
- in cases where we have to investigate the state of the stream, we're doing
unnecessary work
- makes it harder to write debug code (i.e., is a stream reference obtained
from the data value descriptor more than once?)
I plan to introduce the method DataValueDescriptor.hasStream, returning a
boolean.
In addition to the obvious check if the stream variable is non-null, it can
also be used to instruct Derby to treat certain data values as non-streams even
though the underlying value is currently a stream. One example is CHAR and
VARCHAR, whose maximum lengths are so small that they should always be
materialized to avoid the added complexity coming with streams (stream state,
isolation levels - extra lock to keep stream stable?, cloning).
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