Mamta Satoor wrote:
Hi,
The patch for optimizer overrides includes changes in metadata.properties.
I think this change in metadata.properties is going to require some form of
upgrade code so that the sql text stored in the systems tables can be
replaced with new sql text which uses this new form of optimizer overrides.
If I'm following the metadata codepath correctly, I don't _think_ the SQL text
for metadata.properties is actually stored in the system tables. Rather, Derby
reads the "metadata.properties" file (which is part of the classes directory and
is included in the build jars) directly at run time.
To explain why I think this is the case, take "getProcedures()" (which is part
of the Java DatabaseMetaData class) as an example. In the EmbedDatabaseMetaData
class, the getProcedures() call ends up being:
PreparedStatement s = getPreparedQuery(queryName);
s.setString(1, swapNull(catalog));
s.setString(2, swapNull(schemaPattern));
s.setString(3, swapNull(procedureNamePattern));
return s.executeQuery();
"getPreparedQuery()" includes the following line:
String queryText = getQueryDescriptions().getProperty(nameKey);
Then "getQueryDescriptions()" calls "loadQueryDescriptions()", which does some
security checking and ultimately calls "PBloadQueryDescriptions()", which
(finally) calls:
InputStream is = getClass().getResourceAsStream("metadata.properties");
p.load(is);
As a quick (but not by any means exhaustive) check of this, I went and renamed
the "metadata.properties" file in my classes directory to something else, then
tried to call "getProcedures" from a Derby DatabaseMetaData instance after
connecting to (an already created) database. The call failed with an NPE
because the InputStream was not able to find metadata.properties. I then put
the metadata.properties file back and deleted the "getProcedures" statement, to
see what would happen if the file was there but didn't have the query in it.
That failed, too, with an error saying:
Feature not implemented: getProcedures.
So that leads me to believe that the queries are not actually stored in the
database.
As for the stored procedures that Kathey mentioned, those are used for
client-server communication. The client calls these stored procedures, which
are then mapped to the appropriate methods in EmbedDatabaseMetaData (the mapping
occurs in SystemProcedures.java, which is where the stored procedures are
implemented), and thus the same codepath shown above is used.
I wondered if anyone can give me some pointers on how to get started with
upgrade code to achieve this. In the mean time, I will start looking into it
too.
All of that said, I'm not entirely sure what that means for your upgrade
question. But here's my theory:
Even if metadata.properties is different from one version to another, the engine
will only read the metadata.properties file that it has in its build. So as
long as your changes don't modify the stored procedure signatures in any way
(they only change the metadata.properties file), I don't _think_ upgrade is an
issue because nothing in the system table has actually changed.
As for soft upgrade...umm, I tend to lean toward this being a non-issue, as
well, because nothing in the database is actually _changed_ when a metadata
procedure is called. If you soft upgrade to a later version, execute a bunch of
metadata queries, then revert back to an older version and execute a bunch more
metadata queries, everything should still be fine...I think.
But all of that is based on my examination of the metadata codepath; if I've
overlooked or oversimplified, people should feel free to correct me.
Hopefully that's more helpful than confusing,
Army
