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.

                        final DatabaseEntry data = new DatabaseEntry();


                        queue.clear();
                        OperationStatus status;
                        if (batchSize > 1) {
                            Cursor cursor = database.openCursor(null, CursorConfig.DEFAULT);
                            try {
                                status = cursor.getFirst(key, data, null);


                                BatchEvent batch = new BatchEvent();
                                for (int i = 0; status == OperationStatus.SUCCESS && i < batchSize; ++i) {
                                    SimpleEvent event = createEvent(data);
                                    if (event != null) {
                                        batch.addEvent(event);
                                    }
                                    status = cursor.getNext(key, data, null);
                                }
                                try {
                                    manager.send(batch);
                                } catch (Exception ioe) {
                                    LOGGER.error("Error sending events", ioe);
                                    break;
                                }
                                cursor.close();
                                cursor = null;
                                Transaction txn = environment.beginTransaction(null, null);
                                try {
                                    for (Event event : batch.getEvents()) {
                                        try {
                                            Map<String, String> headers = event.getHeaders();
                                            key = new DatabaseEntry(headers.get(FlumeEvent.GUID).getBytes(UTF8));
                                            database.delete(txn, key);
                                        } catch (Exception ex) {
                                            LOGGER.error("Error deleting key from database", ex);
                                        }
                                    }
                                    txn.commit();
                                } catch (Exception ex) {
                                    LOGGER.error("Unable to commit transaction", ex);
                                    if (txn != null) {
                                        txn.abort();
                                    }
                                }
                            } catch (Exception ex) {
                                LOGGER.error("Error reading database", ex);
                                shutdown = true;
                                break;
                            } finally {
                                if (cursor != null) {
                                    cursor.close();
                                }
                            }
                        } else {
                            Transaction txn = environment.beginTransaction(null, null);
                            Cursor cursor = database.openCursor(txn, null);
                            try {
                                status = cursor.getFirst(key, data, LockMode.RMW);
                                while (status == OperationStatus.SUCCESS) {
                                    SimpleEvent event = createEvent(data);
                                    if (event != null) {
                                        try {
                                            manager.doSend(event);
                                        } catch (Exception ioe) {
                                            errors = true;
                                            LOGGER.error("Error sending event", ioe);
                                            break;
                                        }
                                        if (!errors) {
                                            try {
                                                cursor.delete();
                                            } catch (Exception ex) {
                                                LOGGER.error("Unable to delete event", ex);
                                            }
                                        }
                                    }
                                    status = cursor.getNext(key, data, LockMode.RMW);
                                }
                                if (cursor != null) {
                                    cursor.close();
                                    cursor = null;
                                }
                                txn.commit();
                                txn = null;
                            } catch (Exception ex) {
                                LOGGER.error("Error reading or writing to database", ex);
                                shutdown = true;
                                break;
                            } finally {
                                if (cursor != null) {
                                    cursor.close();
                                }
                                if (txn != null) {
                                    txn.abort();
                                }
                            }

View Full Code Here

      try {
         currentTransaction.beginTransaction(null);
         for (Database db : new Database[]{cacheDb, expiryDb}) {
            long recordCount = ois.readLong();
            log.debugf("clearing and reading %s records from stream", recordCount);
            Cursor cursor = null;
            try {
               cursor = db.openCursor(currentTransaction.getTransaction(), null);
               for (int i = 0; i < recordCount; i++) {
                  byte[] keyBytes = (byte[]) ois.readObject();
                  byte[] dataBytes = (byte[]) ois.readObject();


                  DatabaseEntry key = new DatabaseEntry(keyBytes);
                  DatabaseEntry data = new DatabaseEntry(dataBytes);
                  cursor.put(key, data);
               }
            } finally {
               if (cursor != null) cursor.close();
            }
         }
         completeCurrentTransaction(true);
      } catch (Exception caught) {
         completeCurrentTransaction(false);

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         currentTransaction.beginTransaction(null);
         for (Database db : new Database[]{cacheDb, expiryDb}) {
            long recordCount = db.count();
            oos.writeLong(recordCount);
            if (trace) log.tracef("writing %s records to stream", recordCount);
            Cursor cursor = null;
            try {
               cursor = db.openCursor(currentTransaction.getTransaction(), null);
               DatabaseEntry key = new DatabaseEntry();
               DatabaseEntry data = new DatabaseEntry();
               int recordsWritten = 0;
               while (cursor.getNext(key, data, null) ==
                     OperationStatus.SUCCESS) {
                  oos.writeObject(key.getData());
                  oos.writeObject(data.getData());
                  recordsWritten++;
               }
               if (trace) log.tracef("wrote %s records to stream", recordsWritten);
               if (recordsWritten != recordCount)
                  log.unexpectedNumberRecordsWritten(recordCount, recordsWritten);
            } finally {
               if (cursor != null) cursor.close();
            }
         }
         completeCurrentTransaction(true);
      } catch (Exception caught) {
         completeCurrentTransaction(false);

View Full Code Here


        Cursor openCursor(Transaction txn, CursorConfig config)
            throws DatabaseException {


            OperationStatus status;
            Cursor cursor = db.openCursor(txn, config);
            try {
                DatabaseEntry data = BasicIndex.NO_RETURN_ENTRY;
                status = cursor.getSearchKey(key, data, null);
            } catch (DatabaseException e) {
                try {
                    cursor.close();
                } catch (DatabaseException ignored) {}
                throw e;
            }
            if (status == OperationStatus.SUCCESS) {
                return cursor;
            } else {
                cursor.close();
                return null;
            }
        }

View Full Code Here

            this.doKeys = doKeys;
            try {
                cursors = new Cursor[conditions.size()];
                for (int i = 0; i < cursors.length; i += 1) {
                    Condition cond = conditions.get(i);
                    Cursor cursor = cond.openCursor(txn, config);
                    if (cursor == null) {
                        /* Leave joinCursor null. */
                        doClose(null);
                        return;
                    }

View Full Code Here

                        firstException = e;
                    }
                }
            }
            for (int i = 0; i < cursors.length; i += 1) {
                Cursor cursor = cursors[i];
                if (cursor != null) {
                    try {
                        cursor.close();
                        cursors[i] = null;
                    } catch (DatabaseException e) {
                        if (firstException == null) {
                            firstException = e;
                        }

View Full Code Here

                                       KeyRange pkeyRange,
                                       ValueAdapter<V> adapter,
                                       CursorConfig config)
        throws DatabaseException {


        Cursor cursor = db.openCursor(txn, config);
        RangeCursor rangeCursor =
            new RangeCursor(singleKeyRange, pkeyRange, sortedDups, cursor);
        return new SubIndexCursor<V>(rangeCursor, adapter);
    }

View Full Code Here

        if (concurrentDB) {
            cursorConfig = new CursorConfig();
            DbCompat.setWriteCursor(cursorConfig, true);
        } 
        boolean failed = true;
        Cursor cursor = db.openCursor(txn, cursorConfig);
        LockMode lockMode = locking ? LockMode.RMW : null;
        try {
            while (true) {
                OperationStatus status =
                    cursor.getSearchKey(keyEntry, dataEntry, lockMode);
                if (status == OperationStatus.SUCCESS) {
                    E existing =
                        entityBinding.entryToObject(keyEntry, dataEntry);
                    entityBinding.objectToData(entity, dataEntry);
                    cursor.put(keyEntry, dataEntry);
                    failed = false;
                    return existing;
                } else {
                    entityBinding.objectToData(entity, dataEntry);
                    status = cursor.putNoOverwrite(keyEntry, dataEntry);
                    if (status != OperationStatus.KEYEXIST) {
                        failed = false;
                        return null;
                    }
                }
            }
        } finally {
            cursor.close();
            if (autoCommit) {
                if (failed) {
                    txn.abort();
                } else {
                    txn.commit();

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            long count = 0;
            DatabaseEntry key = NO_RETURN_ENTRY;
            DatabaseEntry data = NO_RETURN_ENTRY;
            CursorConfig cursorConfig = locking ?
                CursorConfig.READ_UNCOMMITTED : null;
            Cursor cursor = db.openCursor(null, cursorConfig);
            try {
                OperationStatus status = cursor.getFirst(key, data, null);
                while (status == OperationStatus.SUCCESS) {
                    if (sortedDups) {
                        count += cursor.count();
                    } else {
                        count += 1;
                    }
                    status = cursor.getNextNoDup(key, data, null);
                }
            } finally {
                cursor.close();
            }
            return count;
        }
    }

View Full Code Here

                                       KeyRange range,
                                       ValueAdapter<V> adapter,
                                       CursorConfig config)
        throws DatabaseException {


        Cursor cursor = db.openCursor(txn, config);
        RangeCursor rangeCursor =
            new RangeCursor(range, null/*pkRange*/, sortedDups, cursor);
        return new BasicCursor<V>(rangeCursor, adapter, isUpdateAllowed());
    }

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