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From "Kristian Waagan (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-4563) Avoid unnecessary use of getStream and getStreamWithDescriptor
Date Tue, 23 Feb 2010 12:54:27 GMT

     [ https://issues.apache.org/jira/browse/DERBY-4563?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kristian Waagan updated DERBY-4563:
-----------------------------------

    Attachment: derby-4563-1a-dvd_hasStream.stat
                derby-4563-1a-dvd_hasStream.diff

Attached patch 1a.

The most notable change is that Derby will thrown an exception if a call to getStream or getStreamWithDescriptor
is made on a data type that supports streams (i.e. SQLClob) but that doesn't have a stream.
This indicates that hasStream wasn't called up front to see if the value should be represented
as a stream or not.
Note that streams for values going in to Derby (inserts) will be obtained through the Resetable-interface,
not DataValueDescriptor.

Regression tests passed, patch ready for review.

> 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
>
>         Attachments: derby-4563-1a-dvd_hasStream.diff, derby-4563-1a-dvd_hasStream.stat
>
>
> 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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