[Db-derby Wiki] Update of "MetadataUpgrade" by KnutAndersHatlen

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The following page has been changed by KnutAndersHatlen:
http://wiki.apache.org/db-derby/MetadataUpgrade

New page:
= Metadata and Upgrade =

See [http://db.apache.org/derby/papers/versionupgrade.html] for a
description of Derby's versioning scheme and upgrade mechanisms.

== Background ==

Some of the methods in java.sql.!DatabaseMetaData return a !ResultSet
value. In Derby, these methods execute a stored prepared statement
(SPS) which performs a query and returns a !ResultSet. An SPS is a
compiled query that is stored in SYS.SYSSTATEMENTS. The stored
prepared statements for metadata queries are created when the database
is created. At that point, the queries are read from two property
files, java/engine/org/apache/derby/impl/jdbc/metadata.properties and
java/engine/org/apache/derby/impl/sql/catalog/metadata_net.properties,
compiled and stored in the database.

When moving to another version of Derby, the metadata queries might
have changed due to bug fixes or new features. If one performs a
metadata query against a database created with an older version, the
stored prepared statements from the old version might give incorrect
results. Therefore, Derby needs to have a way to make the metadata
calls use the new queries instead of the old ones.

== Soft Upgrade ==

...

== Full Upgrade ==

...

== Maintenance and Point Releases ==

...