Examples of com.persistit.Tree$TreeVersion

com.persistit.Tree

Cached meta-data about a single B-Tree within a {@link Volume}. A Tree object keeps track of the Volume, the index root page, the index depth, various other statistics and the {@link Accumulator}s for a B-Tree.

As of Persistit 3.3, this class supports version within transactions. A new Tree created within the cope of a {@link Transaction} is notvisible within the other transactions until it commits. Similarly, if a Tree is removed within the scope of a transaction, other transactions that started before the current transaction commits will continue to be able to read and write the Tree. As a side-effect, the physical storage for a Tree is not deallocated until there are no remaining active transactions that started before the commit timestamp of the current transaction. Concurrent transactions that attempt to create or remove the same Tree instance are subject to a a write-write dependency (see {@link Transaction}); all but one such transaction must roll back.

Tree instances are created by {@link Volume#getTree(String,boolean)}. If the Volume already has a B-Tree with the specified name, then the Tree object returned by getTree reflects the stored information. Otherwise, getTree can create a new B-Tree. In either case, the Tree is merely a transient in-memory cache for the B-Tree information ultimately stored on disk.

Persistit ensures that Tree instances are unique, that is, for a given Volume and name, there is only one Tree. if multiple threads call {@link Volume#getTree(String,boolean)} for the samename on the same volume, the first such call will create a new Tree instance and subsequent calls will return the same instance.

Each Tree may have up to 64 {@link Accumulator} instances thatmay be used to aggregate statistical information such as counters. Accumulators work within the MVCC transaction scheme to provide highly concurrent access to a small number of variables that would otherwise cause a significant performance degradation.

    }


    @Override
    public Exchange getExchange(final Session session, final TreeLink link) {
        try {
            final Tree tree = populateTreeCache(link);
            if(!tree.isValid()) {
                throw new IllegalArgumentException("Tree is not valid: " + tree);
            }
            final Exchange exchange = getExchange(session, tree);
            exchange.setAppCache(link);
            return exchange;

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            final String treeName) throws PersistitException {
        Persistit db = getDb();
        final Volume sysVol = db.getSystemVolume();
        for (final Volume volume : db.getVolumes()) {
            if (volume != sysVol) {
                final Tree tree = volume.getTree(treeName, false);
                if (tree != null) {
                    final Exchange exchange = getExchange(session, tree);
                    try {
                        visitor.visit(exchange);
                    } finally {

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        }
    }


    @Override
    public Tree populateTreeCache(final TreeLink link) throws PersistitException {
        Tree tree = link.getTreeCache();
        if (tree == null || !tree.isValid()) {
            tree = dataVolume.getTree(link.getTreeName(), true);
            link.setTreeCache(tree);
        }
        return tree;
    }

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    }


    @Override
    public boolean treeExists(String treeName) {
        try {
            final Tree tree = dataVolume.getTree(treeName, false);
            return tree != null;
        } catch (PersistitException e) {
            throw new PersistitAdapterException(e);
        }
    }

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     * However, Trees aren't normally removed as they are non-transactional in < Persistit 3.3.0.
     */
    @Test
    public void invalidTreeClearsCache() throws Exception {
        final Exchange ex1 = treeService.getExchange(session(), new TestLink("schema", "someTree"));
        final Tree tree = ex1.getTree();
        treeService.releaseExchange(session(), ex1);
        assertFalse(treeService.exchangeQueue(session(), ex1.getTree()).isEmpty());
        final Exchange ex2 = treeService.getExchange(session(), new TestLink("schema", "someTree"));
        final Exchange ex3 = treeService.getExchange(session(), new TestLink("schema", "someTree"));
        treeService.releaseExchange(session(), ex3);

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        PersistitStorageDescription desc = createDescription("tree");
        List<Exchange> exchanges = new ArrayList<>();
        for(int i = 0; i < (MAX_EXCHANGE_CACHE * 5); ++i) {
            exchanges.add(treeService.getExchange(session(), desc));
        }
        Tree tree = exchanges.get(0).getTree();
        for(Exchange ex : exchanges) {
            treeService.releaseExchange(session(), ex);
        }
        assertEquals("cached exchange count", MAX_EXCHANGE_CACHE, getCachedExchangeCount(tree));
    }

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        public void setRowDef(RowDef rowDef) {
            if(rowDef == null) {
                rowCount = autoIncrement = null;
            } else {
                checkExpectedRowDefID(expectedID, rowDef);
                Tree tree = getTreeForRowDef(rowDef);
                rowCount = new AccumulatorAdapter(AccumulatorAdapter.AccumInfo.ROW_COUNT, tree);
                autoIncrement = new AccumulatorAdapter(AccumulatorAdapter.AccumInfo.AUTO_INC, tree);
            }
        }

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