[ http://issues.apache.org/jira/browse/DERBY-424?page=all ]
Mamta A. Satoor resolved DERBY-424:
-----------------------------------
Fix Version: 10.2.0.0
10.1.2.0
Resolution: Fixed
The fix went into both 10.2 and 10.1.2.
Some additional comments on the fix
1)The reason for adding a new method referencesSessionSchema(QueryTreeNode qt)
in GenericPreparedStatement----
If you look at the GenericStatement's prepMinion method, towards the
beginning(line 167 onwards in the review package), we look for the statement in
the cache. If it is found there, we set foundInCache to true. After that, we
check if the statement found in the cache might be referencing SESSION schema
object and if yes, then we do not want to use the statement plan from the
cache, instead we want to build it again. The check to see if statement
references SESSION schema is done by following code in GenericStatement's
prepMinion method
if (foundInCache) {
if (preparedStmt.referencesSessionSchema()) {
// cannot use this state since it is private to a connection.
// switch to a new statement.
foundInCache = false;
preparedStmt = new GenericPreparedStatement(this);
break;
}
}
GenericPreparedStatement or GenericStatement at the time of the check above
donot have the query tree object and hence we can't simply call
qt.referencesSessionSchema. For this reason, I had to add
public boolean referencesSessionSchema(QueryTreeNode qt) to
GenericPreparedStatement(which gets called by the compile phase after the qt
object is constructed) and the method saves the qt object's
referencesSessionSchema() status in it's own local variable
referencesSessionSchema. This local information is what will be used by the
other referencesSessionSchema method to determine if statement found in cache
should be discarded and compile phase should be re-executed.
So, to summarize, the new method after the bind phase, extracts the
referencesSessionSchema information from the passed qt object and saves it in
the local variable.
public boolean referencesSessionSchema(QueryTreeNode qt)
throws StandardException {
//If the query references a SESSION schema table (temporary or permanent),
then mark so in this statement
referencesSessionSchema = qt.referencesSessionSchema();
return(referencesSessionSchema);
}
And, the existing referencesSessionSchema() method as shown below, uses the
local variable (which was filled correctly last time the statement was
compiled) to let the compile phase know if it should ignore the plan found in
the cache and reconstruct the plan because the old plan had references to
SESSION schema objects.
public boolean referencesSessionSchema()
{
return referencesSessionSchema;
}
3)How information about SESSION schema object reference gets lost during
optimization phase-----
At the end of the bind phase for select * from session.st1; GenericStatement's
qt (QueryTreeNode object which in this case is CursorNode) object has it's
resultSet object as a SelectNode which has a fromList object with
referencesSessionSchema field set to true because it was referencing an object
from SESSION schema.
When the optimize code is called on this bound qt object, the optimizer
replaces the SelectNode resultSet object with a ProjectRestrictNode and in that
process, we loose the referencesSessionSchema information which was part of the
SelectNode's FromList object. Rather than trying to have that information some
how be transferred to the new ResultSet object, it is more efficient to use the
information right after bind phase and remove the plan from the statement
cache.
> Queryplan for a query using SESSION schema view is incorrectly put in
> statement cache. This could cause incorrect plan getting executed later if a
> temp. table is created with that name.
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: DERBY-424
> URL: http://issues.apache.org/jira/browse/DERBY-424
> Project: Derby
> Type: Bug
> Components: SQL
> Versions: 10.1.1.0, 10.2.0.0
> Environment: generic
> Reporter: Satheesh Bandaram
> Assignee: Mamta A. Satoor
> Priority: Minor
> Fix For: 10.2.0.0, 10.1.2.0
> Attachments: Derby424SessionSchemaCaching.txt
>
> See DERBY-405 for some discussion related this issue. I suspect this is
> because of statement caching. Derby doesn't seem to recognise we have a
> temporary table that just overloaded an existing physical table.
> It would have been good to avoid permanent tables/views/synonyms in SESSION
> schema. Not sure what we should do now about this, though.
> ij> create view session.st1 as select * from t;
> 0 rows inserted/updated/deleted
> ij> select * from session.st1;
> I |J |K
> -----------------------------------
> 1 |1 |NULL
> 2 |2 |NULL
> 3 |3 |NULL
> 4 |4 |NULL
> 4 rows selected
> ij> select * from t;
> I |J |K
> -----------------------------------
> 1 |1 |NULL
> 2 |2 |NULL
> 3 |3 |NULL
> 4 |4 |NULL
> 4 rows selected
> ij> declare global temporary table st1(c11 int, c12 int) on commit preserve
> rows
> not logged;
> 0 rows inserted/updated/deleted
> ij> select * from session.st1;
> I |J |K
> -----------------------------------
> 1 |1 |NULL
> 2 |2 |NULL
> 3 |3 |NULL
> 4 |4 |NULL
> 4 rows selected
> ij> select * from session.st1; <==== This statement has an extra space
> between FROM and session.st1
> C11 |C12
> -----------------------
> 0 rows selected
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