Examples of com.persistit.Exchange

com.persistit.Exchange
The main facade for fetching, storing and removing records from a Persistit™ database.

Applications interact with Persistit through instances of this class. A Exchange has two important associated member objects, a {@link com.persistit.Key} and a {@link com.persistit.Value}. A Key is a mutable representation of a key, and a Value is a mutable representation of a value. Applications manipulate these objects and interact with the database through one of the following four general patterns:
1. Modify the Key, perform a {@link com.persistit.Exchange#fetch fetch} operation, and query the Value.
2. Modify the Key, modify the Value, and then perform a {@link com.persistit.Exchange#store store} operation to insert or replacedata in the database.
3. Modify the Key, and then perform a {@link com.persistit.Exchange#remove remove} to remove one or more key/valuepairs.
4. Optionally modify the Key, perform a {@link com.persistit.Exchange#traverse traverse} operation, then query theresulting state of Key and/or Value to enumerate key/value pairs currently stored in the database.
Additional methods of Exchange include {@link #fetchAndStore fetchAndStore} and {@link #fetchAndRemove fetchAndRemove} which atomicallymodify the database and return the former value associated with the current Key.

Exchange is Not Threadsafe
Important: an Exchange and its associated Key and Value instances are not thread-safe. Generally each Thread should allocate and use its own Exchange instances. Were it to occur, modification of the Key or Value objects associated with an Exchange by another thread could cause severe and unpredictable errors, including possible corruption of the underlying data storage. While the methods of one Exchange instance are not threadsafe, Persistit is designed to allow multiple threads, using multiple Exchange instances, to access and update the underlying database in a highly concurrent fashion.

Exchange Pools
Normally each thread should allocate its own Exchange instances. However, depending on the garbage collection performance characteristics of a particular JVM it may be desirable to maintain a pool of Exchanges available for reuse, thereby reducing the frequency with which Exchanges need to be constructed and then garbage collected. An application may get an Exchange using {@link Persistit#getExchange(String,String,boolean)} or{@link Persistit#getExchange(Volume,String,boolean)}. These methods reuse a previously constructed Exchange if one is available in a pool; otherwise they construct methods construct a new one. Applications using the Exchange pool should call {@link Persistit#releaseExchange(Exchange,boolean)} to relinquish anExchange once it is no longer needed, thereby placing it in the pool for subsequent reuse.
@version 1.0


        }


        for (String treeName : treeNames) {
            try {
                Exchange ex = new Exchange(db, volume, treeName, false);
                ex.removeTree();
            } catch (PersistitException ex) {
                throw new PermanentStorageException(ex);
            }


        }

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        return getExchange(treeName, true);
    }


    public Exchange getExchange(String treeName, Boolean create) throws StorageException {
        synchronized (this) {
            Exchange exchange;
            try {
                assign();
                exchange = db.getExchange(VOLUME_NAME, treeName, create);
                return exchange;
            } catch (PersistitException ex) {

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        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;
        } catch (PersistitException e) {
            throw PersistitAdapter.wrapPersistitException(session, e);
        }
    }

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    }


    @Override
    public Exchange getExchange(final Session session, final Tree tree) {
        Queue<Exchange> queue = exchangeQueue(session, tree);
        Exchange ex = queue.poll();
        if(ex == null) {
            ex = new Exchange(tree);
        }
        return ex;
    }

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        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 {
                        releaseExchange(session, exchange);
                    }

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    @Override
    public void removeStatistics(Session session, Index index) {
        try {
            RowDef indexStatisticsRowDef = getIndexStatsRowDef(session);
            Exchange exchange = getStore().getExchange(session, indexStatisticsRowDef);
            removeStatisticsInternal(session, index, exchange);
        } catch(PersistitException | RollbackException e) {
            throw PersistitAdapter.wrapPersistitException(session, e);
        }
    }

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    private IndexStatistics loadIndexStatisticsInternal(Session session, Index index) throws PersistitException {
        RowDef indexRowDef = index.leafMostTable().rowDef();
        RowDef indexStatisticsRowDef = getIndexStatsRowDef(session);
        RowDef indexStatisticsEntryRowDef = getIndexStatsEntryRowDef(session);


        Exchange exchange = getStore().getExchange(session, indexStatisticsRowDef);
        exchange.clear()
            .append(indexStatisticsRowDef.table().getOrdinal())
            .append((long)indexRowDef.getRowDefId())
            .append((long)index.getIndexId());
        if (!exchange.fetch().getValue().isDefined()) {
            return null;
        }
        IndexStatistics result = decodeHeader(session, exchange, indexStatisticsRowDef, index);
        while (exchange.traverse(Key.GT, true)) {
            if (exchange.getKey().getDepth() <= indexStatisticsRowDef.getHKeyDepth()) {
                break;          // End of children.
            }
            decodeEntry(session, exchange, indexStatisticsEntryRowDef, result);
        }
        if (logger.isDebugEnabled()) {

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            }
            tempVolumeState.acquire();
            if(injectIOException) {
                throw new PersistitIOException(new IOException());
            }
            Exchange ex = new Exchange(persistit, tempVolumeState.volume(), treeName, true);
            success = true;
            return ex;
        } catch (PersistitException | RollbackException e) {
            if (!PersistitAdapter.isFromInterruption(e))
                LOG.debug("Caught exception while getting exchange for sort", e);

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            this.operation = operation;
        }


        @Override
        public void run(Session session) {
            Exchange exchange = store.createStoreData(session, index);
            key.copyTo(exchange.getKey());
            try {
                checkReferencing(session, index, exchange, row, foreignKey, operation, true);
            }
            finally {
                store.releaseStoreData(session, exchange);

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            this.operation = operation;
        }


        @Override
        public void run(Session session) {
            Exchange exchange = store.createStoreData(session, index);
            key.copyTo(exchange.getKey());
            try {
                // selfReference = false on recheck; we deleted one row.
                checkNotReferenced(session, index, exchange, row, foreignKey, false, action, operation, true);
            }
            finally {

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Examples of com.persistit.Exchange

Exchange is Not Threadsafe

Exchange Pools

Related Classes of com.persistit.Exchange