1. Derby
  2. DERBY-4563

Avoid unnecessary use of getStream and getStreamWithDescriptor


    • Type: Improvement Improvement
    • Status: Closed
    • Priority: Minor Minor
    • Resolution: Fixed
    • Affects Version/s:
    • Fix Version/s:
    • Component/s: JDBC
    • Labels:


      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).

      1. derby-4563-1a-dvd_hasStream.diff
        21 kB
        Kristian Waagan
      2. derby-4563-1a-dvd_hasStream.stat
        1.0 kB
        Kristian Waagan
      3. derby-4563-1b-dvd_hasStream.diff
        21 kB
        Kristian Waagan
      4. derby-4563-2a-replace_streamstorable_in_jdbclayer.diff
        2 kB
        Kristian Waagan



          • Assignee:
            Kristian Waagan
            Kristian Waagan
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