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.

        }
        dupSort = db.getConfig().getSortedDuplicates();


        printHeader(outputFile, dupSort, formatUsingPrintable);


        Cursor cursor = db.openCursor(null, null);
        while (cursor.getNext(foundKey, foundData, LockMode.DEFAULT) ==
               OperationStatus.SUCCESS) {
            dumpOne(outputFile, foundKey.getData(), formatUsingPrintable);
            dumpOne(outputFile, foundData.getData(), formatUsingPrintable);
        }
        cursor.close();
        db.close();
        outputFile.println("DATA=END");


        LoggerUtils.envLogMsg(Level.INFO, DbInternal.getEnvironmentImpl(env),
                              "DbDump.dump of " + dbName + " ending");

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                throw new IllegalStateException(status.toString());
            }
        }


        /* Position a cursor to the first record. */
        final Cursor cursor = db.openCursor(null, null);
        OperationStatus status = cursor.getFirst(keyEntry, dataEntry, null);
        assert status == OperationStatus.SUCCESS;


        /*
         * Calculate BIN size including LNs/data. The recalcKeyPrefix and
         * compactMemory methods are called to simulate normal operation.
         * Normally prefixes are recalculated when a IN is split, and
         * compactMemory is called after fetching a IN or evicting an LN.
         */
        final BIN bin = DbInternal.getCursorImpl(cursor).getBIN();
        bin.recalcKeyPrefix();
        bin.compactMemory();
        minBinSizeWithData = bin.getInMemorySize();


        /* Evict all LNs. */
        for (int i = 0; i < nodeAvg; i += 1) {
            assert status == OperationStatus.SUCCESS;
            final CursorImpl cursorImpl = DbInternal.getCursorImpl(cursor);
            assert bin == cursorImpl.getBIN();
            assert duplicates ?
                (bin.getTarget(i) == null) :
                (bin.getTarget(i) != null);
            if (!duplicates) {
                cursorImpl.evict();
            }
            status = cursor.getNext(keyEntry, dataEntry, null);
        }
        assert status == OperationStatus.NOTFOUND;
        cursor.close();


        /*
         * Calculate BIN size without LNs/data. The clearLsnCompaction method
         * is called to artificially remove LSN compaction savings.  The amount
         * saved by LSN compaction is currently the only difference between the

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            }
            Collections.shuffle(rndKeys, new Random(123));
        }


        final Transaction txn = env.beginTransaction(null, null);
        final Cursor cursor = db.openCursor(txn, null);
        boolean success = false;
        try {
            cursor.setCacheMode(CacheMode.EVICT_LN);
            for (int i = 0; i <= lastKey; i += 1) {
                final int keyVal = orderedInsertion ? i : rndKeys.get(i);
                byte[] keyBytes = padLeft
                    (BigInteger.valueOf(keyVal).toByteArray(), maxKeyBytes);
                setKeyData(keyBytes, keyOffset, keyEntry, dataEntry);


                final OperationStatus status;
                if (duplicates) {
                    status = cursor.putNoDupData(keyEntry, dataEntry);
                } else {
                    status = cursor.putNoOverwrite(keyEntry, dataEntry);
                }
                if (status == OperationStatus.KEYEXIST && !orderedInsertion) {
                    i -= 1;
                    continue;
                }
                if (status != OperationStatus.SUCCESS) {
                    throw new IllegalStateException("Could not insert: " +
                                                    status);
                }


                if (i % 10000 == 0) {
                    final EnvironmentStats stats = env.getStats(null);
                    if (stats.getNNodesScanned() > 0) {
                        throw new IllegalStateException
                            ("*** Ran out of cache memory at record " + i +
                             " -- try increasing Java heap size ***");
                    }
                    if (out != null) {
                        out.print(".");
                        out.flush();
                    }
                }
            }
            success = true;
        } finally {
            cursor.close();
            if (success) {
                txn.commit();
            } else {
                txn.abort();
            }

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      String namePart = "";
      int namePartIndex = name.size();
      Set<String> set = null;


      Cursor cursor = cacheDb.openCursor(null, null);
      try
      {
         while (true)
         {
            DatabaseEntry keyEntry = makeKeyEntry(prefixEntry, namePart);
            OperationStatus status =
                  cursor.getSearchKeyRange(keyEntry, dataEntry, null);
            if (status != OperationStatus.SUCCESS ||
                  !startsWith(keyEntry, prefixEntry))
            {
               break;
            }
            if (set == null)
            {
               set = new HashSet<String>();
            }
            Fqn childName = makeKeyObject(keyEntry);
            namePart = childName.get(namePartIndex).toString();
            set.add(namePart);
            namePart += LOWEST_UTF_CHAR;
         }
      }
      finally
      {
         cursor.close();
      }
      if (set != null)
      {
         return Collections.unmodifiableSet(set);
      }

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      /* To update-or-insert, try putNoOverwrite first, then a RMW cycle. */
      Map<Object, Object> map = new HashMap<Object, Object>();
      map.put(key, value);
      DatabaseEntry dataEntry = makeDataEntry(map);
      DatabaseEntry keyEntry = makeKeyEntry(name);
      Cursor cursor = cacheDb.openCursor(txn, null);
      try
      {
         OperationStatus status = cursor.putNoOverwrite(keyEntry, dataEntry);
         if (status == OperationStatus.SUCCESS)
         {
            createParentNodes(cursor, name);
         }
         else
         {
            DatabaseEntry foundData = new DatabaseEntry();
            status = cursor.getSearchKey(keyEntry, foundData, LockMode.RMW);
            if (status == OperationStatus.SUCCESS)
            {
               map = makeDataObject(foundData);
               oldVal = map.put(key, value);
               cursor.putCurrent(makeDataEntry(map));
            }
         }
      }
      finally
      {
         cursor.close();
      }
      return oldVal;
   }

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      }


      /* To update-or-insert, try putNoOverwrite first, then a RMW cycle. */
      DatabaseEntry dataEntry = makeDataEntry(values);
      DatabaseEntry keyEntry = makeKeyEntry(name);
      Cursor cursor = cacheDb.openCursor(txn, null);
      try
      {
         OperationStatus status = cursor.put(keyEntry, dataEntry);
         if (status == OperationStatus.SUCCESS)
         {
            createParentNodes(cursor, name);
         }
      }
      finally
      {
         cursor.close();
      }
   }

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      // JBCACHE-769 -- make a defensive copy
      values = (values == null ? null : new HashMap<Object, Object>(values));


      DatabaseEntry dataEntry = makeDataEntry(values);
      DatabaseEntry keyEntry = makeKeyEntry(name);
      Cursor cursor = cacheDb.openCursor(txn, null);
      try
      {
         cursor.put(keyEntry, dataEntry);
         createParentNodes(cursor, name);
      }
      finally
      {
         cursor.close();
      }
   }

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      {
         DatabaseEntry keyEntry = makeKeyEntry(name);
         DatabaseEntry foundKey = new DatabaseEntry();
         DatabaseEntry foundData = new DatabaseEntry();
         foundData.setPartial(0, 0, true);
         Cursor cursor = cacheDb.openCursor(txn, null);
         try
         {
            OperationStatus status =
                  cursor.getSearchKey(keyEntry, foundData, LockMode.RMW);
            while (status == OperationStatus.SUCCESS)
            {
               cursor.delete();
               status = cursor.getNext(foundKey, foundData, LockMode.RMW);
               if (status == OperationStatus.SUCCESS &&
                     !startsWith(foundKey, keyEntry))
               {
                  status = OperationStatus.NOTFOUND;
               }
            }
         }
         finally
         {
            cursor.close();
         }
      }
   }

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   {


      Object oldVal = null;
      DatabaseEntry keyEntry = makeKeyEntry(name);
      DatabaseEntry foundData = new DatabaseEntry();
      Cursor cursor = cacheDb.openCursor(txn, null);
      try
      {
         OperationStatus status =
               cursor.getSearchKey(keyEntry, foundData, LockMode.RMW);
         if (status == OperationStatus.SUCCESS)
         {
            Map map = makeDataObject(foundData);
            oldVal = map.remove(key);
            cursor.putCurrent(makeDataEntry(map));
         }
      }
      finally
      {
         cursor.close();
      }
      return oldVal;
   }

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   {


      DatabaseEntry dataEntry = new DatabaseEntry();
      dataEntry.setPartial(0, 0, true);
      DatabaseEntry keyEntry = makeKeyEntry(name);
      Cursor cursor = cacheDb.openCursor(txn, null);
      try
      {
         OperationStatus status =
               cursor.getSearchKey(keyEntry, dataEntry, LockMode.RMW);
         if (status == OperationStatus.SUCCESS)
         {
            cursor.putCurrent(makeDataEntry(null));
         }
      }
      finally
      {
         cursor.close();
      }
   }

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Examples of com.sleepycat.je.Cursor

Using Partial DatabaseEntry Parameters

Related Classes of com.sleepycat.je.Cursor