[Mondrian] Re: VirtualCubeTest.testCalculatedMemberAcrossCubesfailing on SMP

michael bienstein mbienstein at yahoo.fr
Tue Jan 23 07:51:50 EST 2007

Just two thoughts on this:
1) Currently I think that a HashMap is used for the global cache.  HashMap is not safely synchronized.  There is a synchronize block that is too large probably - the whole aggregations data.  
2) Two-tier using threadlocal sounds good.  Can we do this idea:
interface QueryContext {
    Connection getConnection(DataSource ds);
    some sort of common filter for aggregation cache and hierarchy caches
    void dispose();

class QueryContextImpl {
    private HashMap<DataSource, Connection> openConnections = new HashMap<DataSource,Connection>();
    public Connection getConnection(DataSource ds) {
        Connection c = openConnections.get(ds);
        if (c != null) {
            return c;
        try {
            c = ds.getConnection();
            openConnections.put(ds, c);
            return c;
        } catch (SQLException ex) {
            throw new MondrianExceptionOrSomething(ex);
    //TODO some filtering to the global aggregation and hierarchy caches
    public void dispose() {
        for (Connection c : openConnections.valueSet()) {
            try {
            } catch (SQLException ex) {
                log it ...

    private static ThreadLocal<QueryContext> qContext = new ThreadLocal<QueryContext>();
    public static QueryContext getQueryContext() {
        return qContext.get();
    public RolapResult(...) {
        if (!execute) {
            //Going to execute
        QueryContext qc = createQueryContext();
        try {
            //Do execute stuff here
        } finally {
    //Use a property to override the class used?  That way we can configure each Connection specifically?
    public QueryContext createQueryContext() {
        return new QueryContextImpl();
//All places in the code base that use DataSource to obtain a Connection in the context of a query should use:
Connection c = RolapResult.getQueryContext().getConnection(ds);

That way we only open one connection per query and we use the database's transaction system.

I found this hard to do because of the RolapConnection/RolapCube constructors calling each other somehow (can't remember the details).

----- Message d'origine ----
De : Julian Hyde <julianhyde at speakeasy.net>
À : Mondrian developer mailing list <mondrian at pentaho.org>
Envoyé le : Mardi, 23 Janvier 2007, 11h57mn 24s
Objet : RE: [Mondrian] Re: VirtualCubeTest.testCalculatedMemberAcrossCubesfailing on SMP

I think the problem is with how mondrian evaluates members using multiple passes. When the measures are coming from a virtual cube, of course there are multiple real cubes, and each of those has a cell reader. But the code in RolapResult assumes there is only one cell reader.
Mondrian should check the cell readers for all applicable cubes, and only emit a result when all cell readers have been populated.
I haven't implemented the fix yet, but this cause seems very plausible to me.
I'm not exactly sure why this problem surfaced after Bart's change - maybe thread-local caches increased the chances of one cache being populated and another not - or why it appears on SMP machines.
By the way, in an effort to get this working, I removed Bart's RolapStarAggregationKey (a compound key of BitKey and thread id) and moved to a two-tier hashing scheme. The first tier is a ThreadLocal of maps, and the second tier is a map. Threads which want access to the global map just skip the first tier. Given the difficulties obtaining a unique id for a thread, using a ThreadLocal seemed cleaner. So, even though this didn't fix the bug, I'm going to check in.


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