Examples of com.sleepycat.je.Cursor

com.sleepycat.je.Cursor
A database cursor. Cursors are used for operating on collections of records, for iterating over a database, and for saving handles to individual records, so that they can be modified after they have been read.
Cursors which are opened with a transaction instance are transactional cursors and may be used by multiple threads, but only serially. That is, the application must serialize access to the handle. Non-transactional cursors, opened with a null transaction instance, may not be used by multiple threads.

If the cursor is to be used to perform operations on behalf of a transaction, the cursor must be opened and closed within the context of that single transaction.

Once the cursor {@link #close} method has been called, the handle may notbe accessed again, regardless of the {@code close} method's success orfailure, with one exception: the {@code close} method itself may be calledany number of times to simplify error handling.

To obtain a cursor with default attributes:
```
 Cursor cursor = myDatabase.openCursor(txn, null); 
```
To customize the attributes of a cursor, use a CursorConfig object.
```
 CursorConfig config = new CursorConfig(); config.setReadUncommitted(true); Cursor cursor = myDatabase.openCursor(txn, config); 
```
Modifications to the database during a sequential scan will be reflected in the scan; that is, records inserted behind a cursor will not be returned while records inserted in front of a cursor will be returned.

Using Partial DatabaseEntry Parameters

The {@link DatabaseEntry#setPartial DatabaseEntry Partial} property canbe used to optimize in certain cases. This provides varying degrees of performance benefits that depend on the specific operation and use of {@code READ_UNCOMMITTED} isolation, as described below.
When retrieving a record with a {@link Database} or {@link Cursor}method, if only the key is needed by the application then the retrieval of the data item can be suppressed using the Partial property. If {@code setPartial(0, 0, true)} is called for the {@code DatabaseEntry} passed asthe data parameter, the data item will not be returned by the {@code Database} or {@code Cursor} method.
Suppressing the return of the data item potentially has a large performance benefit when the {@code READ_UNCOMMITTED} isolation mode isused. In this case, if the record data is not in the JE cache, it will not be read from disk. The performance benefit is potentially large because random access disk reads may be reduced. Examples are:
- Scanning all records in key order, when the data is not needed and {@code READ_UNCOMMITTED} isolation is acceptable.
- Skipping over records quickly to perform approximate pagination with {@code READ_UNCOMMITTED} isolation.
For other isolation modes ( {@code READ_COMMITTED}, {@code REPEATABLE_READ} and {@code SERIALIZABLE}), the performance benefit is not as significant. In this case, the data item must be read into the JE cache if it is not already present, in order to lock the record. The only performance benefit is that the data will not be copied from the JE cache to the application's entry parameter.

For information on specifying isolation modes, see {@link LockMode}, {@link CursorConfig} and {@link TransactionConfig}.

The Partial property may also be used to retrieve or update only a portion of a data item. This avoids copying the entire record between the JE cache and the application data parameter. However, this feature is not currently fully optimized, since the entire record is always read or written to the database, and the entire record is cached. A partial update may be performed only with {@link Cursor#putCurrent Cursor.putCurrent}.

In limited cases, the Partial property may also be used to retrieve a partial key item. For example, a {@code DatabaseEntry} with a Partialproperty may be passed to {@link #getNext getNext}. However, in practice this has limited value since the entire key is usually needed by the application, and the benefit of copying a portion of the key is generally very small. Partial key items may not be passed to methods that use the key as an input parameter, for example, {@link #getSearchKey getSearchKey}. In general, the usefulness of partial key items is very limited.

     * All rep group db access uses cursors with eviction disabled.
     */
    static private Cursor makeCursor(DatabaseImpl dbImpl,
                                     Txn txn,
                                     CursorConfig cursorConfig) {
        Cursor cursor = DbInternal.makeCursor(dbImpl,
                                              txn,
                                              cursorConfig);
        DbInternal.getCursorImpl(cursor).setAllowEviction(false);
        return cursor;
    }

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        Map <Integer, RepNodeImpl> nodes =
            new HashMap<Integer, RepNodeImpl>();
        final CursorConfig cursorConfig = new CursorConfig();
        cursorConfig.setReadCommitted(true);


        Cursor mcursor = null;


        try {
            mcursor = makeCursor(dbImpl, txn, cursorConfig);
            while (mcursor.getNext(keyEntry, value, LockMode.DEFAULT) ==
                   OperationStatus.SUCCESS) {


                final String key = StringBinding.entryToString(keyEntry);


                if (GROUP_KEY.equals(key)) {
                    group = groupBinding.entryToObject(value);
                    if (!group.getName().equals(groupName)) {
                        throw EnvironmentFailureException.unexpectedState
                            ("The argument: " + groupName +
                             " does not match the expected group name: " +
                             group.getName());
                    }
                } else {
                    final RepNodeImpl mi = miBinding.entryToObject(value);
                    nodes.put(mi.getNameIdPair().getId(), mi);
                }
            }
            if (group == null) {
                throw EnvironmentFailureException.unexpectedState
                    ("Group key: " + GROUP_KEY + " is missing");
            }
            group.setNodes(nodes);
            return group;
        } finally {
            if (mcursor != null) {
                mcursor.close();
            }
        }
    }

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        /* Create the common group entry. */
        TransactionConfig txnConfig = new TransactionConfig();
        txnConfig.setDurability(NO_ACK.getDurability());
        txnConfig.setConsistencyPolicy(NO_CONSISTENCY);
        Txn txn = null;
        Cursor cursor = null;
        try {
            txn = new MasterTxn(repImpl,
                                txnConfig,
                                repImpl.getNameIdPair());


            cursor = makeCursor(groupDbImpl, txn, CursorConfig.DEFAULT);
            OperationStatus status = cursor.put(groupKeyEntry, groupEntry);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Couldn't write first group entry " + status);
            }
            cursor.close();
            cursor = null;
            txn.commit();
            txn = null;
        } finally {
            if (cursor != null) {
                cursor.close();
            }


            if (txn != null) {
                txn.abort();
            }

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        DatabaseEntry value = new DatabaseEntry();
        final RepGroupDB.NodeBinding mib = new RepGroupDB.NodeBinding();


        Txn txn = null;
        Cursor cursor = null;
        try {
            txn = new ReadonlyTxn(repImpl, NO_ACK);
            CursorConfig config = new CursorConfig();
            config.setReadCommitted(true);
            cursor = makeCursor(groupDbImpl, txn, config);


            OperationStatus status =
                cursor.getSearchKey(nodeNameKey, value, null);
            if (status == OperationStatus.SUCCESS) {
                /* Let's see if the entry needs updating. */
                RepNodeImpl miInDb = mib.entryToObject(value);
                if (miInDb.equivalent(ensureNode)) {
                    if (miInDb.isQuorumAck()) {
                        /* Present, matched and acknowledged. */
                        return;
                    }
                    ensureNode.getNameIdPair().update(miInDb.getNameIdPair());
                    /* Not acknowledged, retry the update. */
                } else {
                    /* Present but not equivalent. */
                    LoggerUtils.warning(logger, repImpl,
                                        "Incompatible node descriptions. " +
                                        "Membership database definition: " +
                                        miInDb.toString() +
                                        " Transient definition: " +
                                        ensureNode.toString());
                    throw EnvironmentFailureException.unexpectedState
                        ("Incompatible node descriptions for node ID: " +
                         ensureNode.getNodeId());
                }
                LoggerUtils.info(logger, repImpl,
                                 "Present but not ack'd node: " +
                                 ensureNode.getNodeId() +
                                 " ack status: " + miInDb.isQuorumAck());
            }
            cursor.close();
            cursor = null;
            txn.commit();
            txn = null;
        } finally {
            if (cursor != null) {
                cursor.close();
            }


            if (txn != null) {
                txn.abort();
            }

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        final RepGroupDB.NodeBinding mib = new RepGroupDB.NodeBinding();
        final RepGroupImpl.BarrierState barrierState =
            new RepGroupImpl.BarrierState(newCBVLSN,
                                          System.currentTimeMillis());
        Txn txn = null;
        Cursor cursor = null;
        boolean ok = false;
        try {
            txn = new MasterTxn(repImpl,
                                NO_ACK_NO_SYNC,
                                repImpl.getNameIdPair());
            cursor = makeCursor(groupDbImpl, txn, CursorConfig.DEFAULT);


            OperationStatus status =
                    cursor.getSearchKey(nodeNameKey, value, LockMode.RMW);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Node ID: " + nameIdPair + " not present in group db");
            }


            /* Let's see if the entry needs updating. */
            RepNodeImpl node = mib.entryToObject(value);
            final VLSN lastCBVLSN = node.getBarrierState().getLastCBVLSN();
            if (lastCBVLSN.equals(newCBVLSN)) {
                ok = true;
                return true;
            }


            node.setBarrierState(barrierState);
            mib.objectToEntry(node, value);
            status = cursor.putCurrent(value);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Node ID: " + nameIdPair +
                     " stored localCBVLSN could not be updated. Status: " +
                     status);
            }
            LoggerUtils.fine(logger, repImpl,
                             "Local CBVLSN updated to " + newCBVLSN +
                             " for node " + nameIdPair);
            ok = true;
        } finally {
            if (cursor != null) {
                cursor.close();
            }


            if (txn != null) {
                if (ok) {
                    txn.commit(NO_ACK_NO_SYNC_DURABILITY);

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        throws DatabaseException {


        RepGroupDB.GroupBinding groupBinding = new RepGroupDB.GroupBinding();
        DatabaseEntry groupEntry = new DatabaseEntry();


        Cursor cursor = null;
        try {
            cursor = makeCursor(groupDbImpl, txn, CursorConfig.DEFAULT);


            OperationStatus status = cursor.getSearchKey(groupKeyEntry,
                                                         groupEntry,
                                                         LockMode.RMW);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Group entry key: " + GROUP_KEY +
                     " missing from group database");
            }
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }


        return groupBinding.entryToObject(groupEntry);
    }

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        RepGroupDB.GroupBinding groupBinding = new RepGroupDB.GroupBinding();
        DatabaseEntry groupEntry = new DatabaseEntry();
        groupBinding.objectToEntry(repGroup, groupEntry);


        Cursor cursor = null;
        try {
            cursor = makeCursor(groupDbImpl, txn, CursorConfig.DEFAULT);


            OperationStatus status =  cursor.put(groupKeyEntry, groupEntry);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Group entry save failed");
            }
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }

View Full Code Here

        final RepGroupDB.NodeBinding nodeBinding =
            new RepGroupDB.NodeBinding();
        DatabaseEntry memberInfoEntry = new DatabaseEntry();
        nodeBinding.objectToEntry(node, memberInfoEntry);


        Cursor cursor = null;
        try {
            cursor = makeCursor(groupDbImpl, txn, CursorConfig.DEFAULT);


            OperationStatus status =  cursor.put(nodeNameKey, memberInfoEntry);
            if (status != OperationStatus.SUCCESS) {
                throw EnvironmentFailureException.unexpectedState
                    ("Group entry save failed");
            }
        } finally {
            if (cursor != null) {
                cursor.close();
            }
        }
    }

View Full Code Here


        txn = new MasterTxn(repImpl, txnConfig, nameIdPair);


        final CursorConfig cursorConfig = new CursorConfig();
        cursorConfig.setReadCommitted(true);
        Cursor mcursor = makeCursor(dbImpl, txn, cursorConfig);


        while (mcursor.getNext(keyEntry, value, LockMode.DEFAULT) ==
               OperationStatus.SUCCESS) {
            final String key = StringBinding.entryToString(keyEntry);


            if (GROUP_KEY.equals(key)) {
                GroupBinding groupBinding = new GroupBinding();
                RepGroupImpl repGroup = new RepGroupImpl(groupName);
                repGroup.setNodeIdSequence(nodeIdSequenceStart);
                DatabaseEntry groupEntry = new DatabaseEntry();
                groupBinding.objectToEntry(repGroup, groupEntry);
                OperationStatus status = mcursor.putCurrent(groupEntry);
                if (!OperationStatus.SUCCESS.equals(status)) {
                    throw new IllegalStateException("Unexpected state:" +
                                                    status);
                }
            } else {
                LoggerUtils.info(logger, repImpl, "Removing node: " + key);
                mcursor.delete();
            }
        }
        mcursor.close();
        txn.commit();


        /* Now add the first node of the new group. */
        ensureMember(firstNode);
        if (firstNodeId != firstNode.getNodeId()) {

View Full Code Here

                DbCompat.setWriteCursor(cdbConfig, true);
            } else {
                cursors = cdbCursors.readCursors;
                cdbConfig = null;
            }
            Cursor cursor;
            if (cursors.size() > 0) {
                Cursor other = ((Cursor) cursors.get(0));
                cursor = other.dup(false);
            } else {
                cursor = db.openCursor(null, cdbConfig);
            }
            cursors.add(cursor);
            return cursor;

View Full Code Here

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Examples of com.sleepycat.je.Cursor

Using Partial DatabaseEntry Parameters

Related Classes of com.sleepycat.je.Cursor