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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Created: (DERBY-4563) Avoid unnecessary use of getStream and getStreamWithDescriptor
Date Tue, 23 Feb 2010 12:42:27 GMT
Avoid unnecessary use of getStream and getStreamWithDescriptor
--------------------------------------------------------------

                 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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