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

        this.securityService = securityService;
    }


    @Override
    public void addOnlineHandledHKey(Session session, int tableID, Key hKey) {
        Exchange ex = onlineHandledHKeyExchange(session, tableID);
        try {
            ex.clear().getKey().appendByteArray(hKey.getEncodedBytes(), 0, hKey.getEncodedSize());
            ex.store();
        } catch(PersistitException | RollbackException e) {
            throw wrapPersistitException(session, e);
        } finally {
            treeService.releaseExchange(session, ex);
        }

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        }
    }


    @Override
    public Iterator<byte[]> getOnlineHandledHKeyIterator(final Session session, int tableID, Key hKey) {
        final Exchange ex = onlineHandledHKeyExchange(session, tableID);
        if(hKey != null) {
            ex.clear().getKey().appendByteArray(hKey.getEncodedBytes(), 0, hKey.getEncodedSize());
        }
        return new Iterator<byte[]>() {
            private Key.Direction dir = Key.GTEQ;


            @Override
            public boolean hasNext() {
                throw new UnsupportedOperationException();
            }


            @Override
            public byte[] next() {
                try {
                    if(!ex.traverse(dir, true)) {
                        return null;
                    }
                    dir = Direction.GT;
                    return ex.getKey().decodeByteArray();
                } catch(PersistitException | RollbackException e) {
                    throw wrapPersistitException(session, e);
                }
            }

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    }


    @Override
    public void setOnlineDMLError(Session session, int tableID, String message) {
        OnlineSession onlineSession = getOnlineSession(session, true);
        Exchange ex = schemaTreeExchange(session);
        try {
            ex.clear().append(S_K_ONLINE).append(onlineSession.id).append(S_K_ERROR);
            ex.getValue().putString(message);
            ex.store();
        } catch(PersistitException | RollbackException e) {
            if(ex != null) {
                treeService.releaseExchange(session, ex);
            }
            throw wrapPersistitException(session, e);

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    }


    @Override
    public String getOnlineDMLError(Session session) {
        OnlineSession onlineSession = getOnlineSession(session, true);
        Exchange ex = schemaTreeExchange(session);
        try {
            ex.clear().append(S_K_ONLINE).append(onlineSession.id).append(S_K_ERROR);
            ex.fetch();
            // write skew
            ex.lock();
            return ex.getValue().isDefined() ? ex.getValue().getString() : null;
        } catch(PersistitException | RollbackException e) {
            if(ex != null) {
                treeService.releaseExchange(session, ex);
            }
            throw wrapPersistitException(session, e);

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    @Override
    public void addOnlineChangeSet(Session session, ChangeSet changeSet) {
        OnlineSession onlineSession = getOnlineSession(session, true);
        onlineSession.tableIDs.add(changeSet.getTableId());
        Exchange ex = schemaTreeExchange(session);
        try {
            ex.clear().append(S_K_ONLINE).append(onlineSession.id).append(S_K_CHANGE).append(changeSet.getTableId());
            ex.getValue().putByteArray(ChangeSetHelper.save(changeSet));
            ex.store();
        } catch(PersistitException | RollbackException e) {
            if(ex != null) {
                treeService.releaseExchange(session, ex);
            }
            throw wrapPersistitException(session, e);

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    }


    void treeWasRemoved(Session session, String schema, String treeName) {
        LOG.debug("Delaying removal of tree (until next restart): {}", treeName);
        delayedTreeCount.incrementAndGet();
        Exchange ex = schemaTreeExchange(session);
        try {
            long id = delayedTreeIDGenerator.incrementAndGet();
            long timestamp = System.currentTimeMillis();
            ex.clear().append(S_K_DELAYED).append(id).append(timestamp);
            ex.getValue().setStreamMode(true);
            ex.getValue().put(schema);
            ex.getValue().put(treeName);
            ex.getValue().setStreamMode(false);
            ex.store();
        } catch(PersistitException | RollbackException e) {
            throw wrapPersistitException(session, e);
        } finally {
            treeService.releaseExchange(session, ex);
        }

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    @Override
    protected void storedAISChange(Session session,
                                   AkibanInformationSchema newAIS,
                                   Collection<String> schemaNames) {
        ByteBuffer buffer = null;
        Exchange ex = null;
        try {
            createValidatedShared(session, newAIS, GenValue.NEW, GenMap.NO_PUT);


            for(String schema : schemaNames) {
                ex = schemaTreeExchange(session);
                saveMetaAndDataVersions(ex);
                ex.clear().append(S_K_PROTOBUF).append(schema);
                buffer = storeProtobuf(ex, buffer, newAIS, schema);
                treeService.releaseExchange(session, ex);
                ex = null;
            }
            buildRowDefs(session, newAIS);

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            }
        }
    }


    private void serializeMemoryTables(Session session, AkibanInformationSchema newAIS) {
        Exchange ex = null;
        try {
            ex = schemaTreeExchange(session);
            saveMemoryTables(ex, newAIS);
            treeService.releaseExchange(session, ex);
            ex = null;

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    @Override
    protected void storedOnlineChange(Session session,
                                      OnlineSession onlineSession,
                                      AkibanInformationSchema newAIS,
                                      Collection<String> schemas) {
        Exchange ex = schemaTreeExchange(session);
        try {
            // Get a unique generation for this AIS, but will only be visible to owning session
            createValidatedShared(session, newAIS, GenValue.NEW, GenMap.NO_PUT);


            // And a new generation for the current so no one else will think the one for newAIS is theirs
            getNextGeneration(session);


            saveMetaAndDataVersions(ex);


            // online,cid => generation
            ex.clear().append(S_K_ONLINE).append(onlineSession.id);
            ex.getValue().put(newAIS.getGeneration());
            ex.store();


            // online,cid,protobuf,schema = bytes
            ByteBuffer buffer = null;
            ex.append(S_K_PROTOBUF).append("");
            for(String name : schemas) {
                ex.to(name);
                buffer = storeProtobuf(ex, buffer, newAIS, name);
            }


            addCallbacksForAISChange(session);
        } catch(PersistitException | RollbackException e) {

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        }
    }


    @Override
    protected void clearOnlineState(Session session, OnlineSession onlineSession) {
        Exchange ex = schemaTreeExchange(session);
        try {
            ex.clear().append(S_K_ONLINE).append(onlineSession.id);
            ex.remove(Key.GTEQ);
            for(int tid : onlineSession.tableIDs) {
                String treeName = onlineHandledHKeyTreeName(onlineSession.id, tid);
                if(treeService.treeExists(treeName)) {
                    Exchange changeEx = onlineHandledHKeyExchange(session, onlineSession.id, tid);
                    //
                    // remove() would be preferable but Persistit will block until transactions
                    // and journal can be fully pruned. Instead, clear and track for delayed.
                    //
                    changeEx.removeAll();
                    nameGenerator.generatedTreeName(treeName);
                    treeWasRemoved(session, SCHEMA_TREE_NAME, treeName);
                }
            }
        } catch(PersistitException | RollbackException e) {

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Examples of com.persistit.Exchange

Exchange is Not Threadsafe

Exchange Pools

Related Classes of com.persistit.Exchange