Package com.apple.foundationdb

Interface ReadTransaction

All Superinterfaces:
ReadTransactionContext
All Known Subinterfaces:
Transaction
public interface ReadTransaction extends ReadTransactionContext
A read-only subset of a FoundationDB Transaction. This is the interface that Transaction's snapshot presents.

Note: Client must call Transaction.commit() and wait on the result on all transactions, even ones that only read. This is done automatically when using the retry loops from Database.run(java.util.function.Function). This is explained more in the intro to Transaction.
See Also:

  • Field Details

    • ROW_LIMIT_UNLIMITED

      static final int ROW_LIMIT_UNLIMITED
      When passed to a getRange() call that takes a limit parameter, indicates that the query should return unlimited rows.
      See Also:

  • Method Details

    • isSnapshot

      boolean isSnapshot()
      Gets whether this transaction is a snapshot view of the database. In other words, this returns whether read conflict ranges are omitted for any reads done through this ReadTransaction.
      For more information about how to use snapshot reads correctly, see Using snapshot reads.
      Returns:
      whether this is a snapshot view of the database with relaxed isolation properties
      See Also:

    • snapshot

      ReadTransaction snapshot()
      Return a special-purpose, read-only view of the database. Reads done through this interface are known as "snapshot reads". Snapshot reads selectively relax FoundationDB's isolation property, reducing Transaction conflicts but making reasoning about concurrency harder.

      For more information about how to use snapshot reads correctly, see Using snapshot reads.
      Returns:
      a read-only view of this ReadTransaction with relaxed isolation properties

    • getReadVersion

      CompletableFuture<Long> getReadVersion()
      Gets the version at which the reads for this Transaction will access the database.
      Returns:
      the version for database reads

    • setReadVersion

      void setReadVersion(long version)
      Directly sets the version of the database at which to execute reads. The normal operation of a transaction is to determine an appropriately recent version; this call overrides that behavior. If the version is set too far in the past, transaction_too_old errors will be thrown from read operations. Infrequently used.
      Parameters:
      version - the version at which to read from the database

    • addReadConflictRangeIfNotSnapshot

      boolean addReadConflictRangeIfNotSnapshot(byte[] keyBegin, byte[] keyEnd)
      Adds the read conflict range that this ReadTransaction would have added as if it had read the given key range. If this is a snapshot view of the database, this will not add the conflict range. This mirrors how reading a range through a snapshot view of the database does not add a conflict range for the read keys.
      Parameters:
      keyBegin - the first key in the range (inclusive)
      keyEnd - the last key in the range (exclusive)
      Returns:
      true if the read conflict range was added and false otherwise
      See Also:

    • addReadConflictKeyIfNotSnapshot

      boolean addReadConflictKeyIfNotSnapshot(byte[] key)
      Adds the read conflict range that this ReadTransaction would have added as if it had read the given key. If this is a snapshot view of the database, this will not add the conflict range. This mirrors how reading a key through a snapshot view of the database does not add a conflict range for the read key.
      Parameters:
      key - the key to add to the read conflict range set (it this is not a snapshot view of the database)
      Returns:
      true if the read conflict key was added and false otherwise
      See Also:

    • get

      CompletableFuture<byte[]> get(byte[] key)
      Gets a value from the database. The call will return null if the key is not present in the database.
      Parameters:
      key - the key whose value to fetch from the database
      Returns:
      a CompletableFuture which will be set to the value corresponding to the key or to null if the key does not exist.

    • getKey

      CompletableFuture<byte[]> getKey(KeySelector selector)
      Returns the key referenced by the specified KeySelector. By default, the key is cached for the duration of the transaction, providing a potential performance benefit. However, the value of the key is also retrieved, using network bandwidth. Invoking setReadYourWritesDisable will avoid both the caching and the increased network bandwidth.
      Parameters:
      selector - the relative key location to resolve
      Returns:
      a CompletableFuture which will be set to an absolute database key
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(KeySelector begin, KeySelector end)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by KeySelectors, with the begin KeySelector inclusive and the end KeySelector exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(KeySelector begin, KeySelector end, int limit)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by KeySelectors, with the begin KeySelector inclusive and the end KeySelector exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(KeySelector begin, KeySelector end, int limit, boolean reverse)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by KeySelectors, with the begin KeySelector inclusive and the end KeySelector exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(KeySelector begin, KeySelector end, int limit, boolean reverse, StreamingMode mode)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by KeySelectors, with the begin KeySelector inclusive and the end KeySelector exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      mode - provide a hint about how the results are to be used. This can provide speed improvements or efficiency gains based on the caller's knowledge of the upcoming access pattern.

      When converting the result of this query to a list using AsyncIterable.asList() with the ITERATOR streaming mode, the query is automatically modified to fetch results in larger batches. This is done because it is known in advance that the AsyncIterable.asList() function will fetch all results in the range. If a limit is specified, the EXACT streaming mode will be used, and otherwise it will use WANT_ALL. To achieve comparable performance when iterating over an entire range without using AsyncIterable.asList(), the same streaming mode would need to be used.

      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(byte[] begin, byte[] end)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(byte[] begin, byte[] end, int limit)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(byte[] begin, byte[] end, int limit, boolean reverse)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(byte[] begin, byte[] end, int limit, boolean reverse, StreamingMode mode)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      mode - provide a hint about how the results are to be used. This can provide speed improvements or efficiency gains based on the caller's knowledge of the upcoming access pattern.

      When converting the result of this query to a list using AsyncIterable.asList() with the ITERATOR streaming mode, the query is automatically modified to fetch results in larger batches. This is done because it is known in advance that the AsyncIterable.asList() function will fetch all results in the range. If a limit is specified, the EXACT streaming mode will be used, and otherwise it will use WANT_ALL. To achieve comparable performance when iterating over an entire range without using AsyncIterable.asList(), the same streaming mode would need to be used.

      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(Range range)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive. Ranges are returned from calls to Tuple.range() and Range.startsWith(byte[]).

      Note: users of older version of the API should replace old calls to getRangeStartsWith( k ) with getRange(Range.startsWith( k ))
      Parameters:
      range - the range of keys to return
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(Range range, int limit)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive. Ranges are returned from calls to Tuple.range() and Range.startsWith(byte[]).

      Note: users of older version of the API should replace old calls to getRangeStartsWith( k ) with getRange(Range.startsWith( k ))
      Parameters:
      range - the range of keys to return
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(Range range, int limit, boolean reverse)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive. Ranges are returned from calls to Tuple.range() and Range.startsWith(byte[]).

      Note: users of older version of the API should replace old calls to getRangeStartsWith( k ) with getRange(Range.startsWith( k ))
      Parameters:
      range - the range of keys to return
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getRange

      AsyncIterable<KeyValue> getRange(Range range, int limit, boolean reverse, StreamingMode mode)
      Gets an ordered range of keys and values from the database. The begin and end keys are specified by byte[] arrays, with the begin key inclusive and the end key exclusive. Ranges are returned from calls to Tuple.range() and Range.startsWith(byte[]).

      Note: users of older version of the API should replace old calls to getRangeStartsWith( k ) with getRange(Range.startsWith( k ))
      Parameters:
      range - the range of keys to return
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      mode - provide a hint about how the results are to be used. This can provide speed improvements or efficiency gains based on the caller's knowledge of the upcoming access pattern.

      When converting the result of this query to a list using AsyncIterable.asList() with the ITERATOR streaming mode, the query is automatically modified to fetch results in larger batches. This is done because it is known in advance that the AsyncIterable.asList() function will fetch all results in the range. If a limit is specified, the EXACT streaming mode will be used, and otherwise it will use WANT_ALL. To achieve comparable performance when iterating over an entire range without using AsyncIterable.asList(), the same streaming mode would need to be used.

      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getMappedRange

      AsyncIterable<MappedKeyValue> getMappedRange(KeySelector begin, KeySelector end, byte[] mapper, int limit, boolean reverse, StreamingMode mode)
      WARNING: This feature is considered experimental at this time. It is only allowed when using snapshot isolation AND disabling read-your-writes.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      mapper - defines how to map a key-value pair (one of the key-value pairs got from the first range query) to a GetRange (or GetValue) request. more details: https://github.com/apple/foundationdb/wiki/Everything-about-GetMappedRange
      limit - the maximum number of results to return. Limits results to the first keys in the range. Pass ROW_LIMIT_UNLIMITED if this query should not limit the number of results. If reverse is true rows will be limited starting at the end of the range.
      reverse - return results starting at the end of the range in reverse order. Reading ranges in reverse is supported natively by the database and should have minimal extra cost.
      mode - provide a hint about how the results are to be used. This can provide speed improvements or efficiency gains based on the caller's knowledge of the upcoming access pattern.

      When converting the result of this query to a list using AsyncIterable.asList() with the ITERATOR streaming mode, the query is automatically modified to fetch results in larger batches. This is done because it is known in advance that the AsyncIterable.asList() function will fetch all results in the range. If a limit is specified, the EXACT streaming mode will be used, and otherwise it will use WANT_ALL. To achieve comparable performance when iterating over an entire range without using AsyncIterable.asList(), the same streaming mode would need to be used.

      Returns:
      a handle to access the results of the asynchronous call
      See Also:

    • getEstimatedRangeSizeBytes

      CompletableFuture<Long> getEstimatedRangeSizeBytes(byte[] begin, byte[] end)
      Gets an estimate for the number of bytes stored in the given range. Note: the estimated size is calculated based on the sampling done by FDB server. The sampling algorithm works roughly in this way: the larger the key-value pair is, the more likely it would be sampled and the more accurate its sampled size would be. And due to that reason it is recommended to use this API to query against large ranges for accuracy considerations. For a rough reference, if the returned size is larger than 3MB, one can consider the size to be accurate.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      Returns:
      a handle to access the results of the asynchronous call

    • getEstimatedRangeSizeBytes

      CompletableFuture<Long> getEstimatedRangeSizeBytes(Range range)
      Gets an estimate for the number of bytes stored in the given range. Note: the estimated size is calculated based on the sampling done by FDB server. The sampling algorithm works roughly in this way: the larger the key-value pair is, the more likely it would be sampled and the more accurate its sampled size would be. And due to that reason it is recommended to use this API to query against large ranges for accuracy considerations. For a rough reference, if the returned size is larger than 3MB, one can consider the size to be accurate.
      Parameters:
      range - the range of the keys
      Returns:
      a handle to access the results of the asynchronous call

    • getRangeSplitPoints

      CompletableFuture<KeyArrayResult> getRangeSplitPoints(byte[] begin, byte[] end, long chunkSize)
      Gets a list of keys that can split the given range into (roughly) equally sized chunks based on chunkSize. Note: the returned split points contain the start key and end key of the given range.
      Parameters:
      begin - the beginning of the range (inclusive)
      end - the end of the range (exclusive)
      chunkSize - -- undocumented
      Returns:
      a handle to access the results of the asynchronous call

    • getRangeSplitPoints

      CompletableFuture<KeyArrayResult> getRangeSplitPoints(Range range, long chunkSize)
      Gets a list of keys that can split the given range into (roughly) equally sized chunks based on chunkSize Note: the returned split points contain the start key and end key of the given range.
      Parameters:
      range - the range of the keys
      chunkSize - -- undocumented
      Returns:
      a handle to access the results of the asynchronous call

    • getBlobGranuleRanges

      CompletableFuture<KeyRangeArrayResult> getBlobGranuleRanges(byte[] begin, byte[] end, int rowLimit)
      Gets the blob granule ranges for a given region. Returned in batches, requires calling again moving the begin key up.
      Parameters:
      begin - beginning of the range (inclusive)
      end - end of the range (exclusive)
      rowLimit - the limit on the number of returned rows
      Returns:
      list of blob granules in the given range. May not be all.

    • options

      TransactionOptions options()
      Returns a set of options that can be set on a Transaction
      Returns:
      a set of transaction-specific options affecting this Transaction