Package org.apache.accumulo.core.iterators

Interface SortedKeyValueIterator<K extends org.apache.hadoop.io.WritableComparable<?>,​V extends org.apache.hadoop.io.Writable>

    • Method Detail

      • hasTop

        boolean hasTop()
        Returns true if the iterator has more elements. Note that if this iterator has yielded (@see YieldingKeyValueIterator.enableYielding(YieldCallback)), this this method must return false.
        Returns:
        true if the iterator has more elements.
        Throws:
        IllegalStateException - if called before seek.

      • next

        void next()
   throws IOException
        Advances to the next K,V pair. Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.
        Throws:
        IOException - if an I/O error occurs.
        IllegalStateException - if called before seek.
        NoSuchElementException - if next element doesn't exist.

      • seek

        void seek​(Range range,
          Collection<ByteSequence> columnFamilies,
          boolean inclusive)
   throws IOException
        Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns. An iterator does not have to stop at the end of the range. The whole range is provided so that iterators can make optimizations. Seek may be called multiple times with different parameters after init(org.apache.accumulo.core.iterators.SortedKeyValueIterator<K, V>, java.util.Map<java.lang.String, java.lang.String>, org.apache.accumulo.core.iterators.IteratorEnvironment) is called. Iterators that examine groups of adjacent key/value pairs (e.g. rows) to determine their top key and value should be sure that they properly handle a seek to a key in the middle of such a group (e.g. the middle of a row). Even if the client always seeks to a range containing an entire group (a,c), the tablet server could send back a batch of entries corresponding to (a,b], then reseek the iterator to range (b,c) when the scan is continued. columnFamilies is used, at the lowest level, to determine which data blocks inside of an RFile need to be opened for this iterator. This set of data blocks is also the set of locality groups defined for the given table. If no columnFamilies are provided, the data blocks for all locality groups inside of the correct RFile will be opened and seeked in an attempt to find the correct start key, regardless of the startKey in the range. In an Accumulo instance in which multiple locality groups exist for a table, it is important to ensure that columnFamilies is properly set to the minimum required column families to ensure that data from separate locality groups is not inadvertently read.
        Parameters:
        range - Range of keys to iterate over.
        columnFamilies - Collection of column families to include or exclude.
        inclusive - boolean that indicates whether to include (true) or exclude (false) column families.
        Throws:
        IOException - if an I/O error occurs.
        IllegalArgumentException - if there are problems with the parameters.

      • getTopKey

        K getTopKey()
        Returns top key. Can be called 0 or more times without affecting behavior of next() or hasTop(). Note that in minor compaction scope and in non-full major compaction scopes the iterator may see deletion entries. These entries should be preserved by all iterators except ones that are strictly scan-time iterators that will never be configured for the minc or majc scopes. Deletion entries are only removed during full major compactions.

        For performance reasons, iterators reserve the right to reuse objects returned by getTopKey when next() is called, changing the data that the object references. Iterators that need to save an object returned by getTopKey ought to copy the object's data into a new object in order to avoid aliasing bugs.

        Returns:
        K
        Throws:
        IllegalStateException - if called before seek.
        NoSuchElementException - if top element doesn't exist.

      • getTopValue

        V getTopValue()
        Returns top value. Can be called 0 or more times without affecting behavior of next() or hasTop().

        For performance reasons, iterators reserve the right to reuse objects returned by getTopValue when next() is called, changing the underlying data that the object references. Iterators that need to save an object returned by getTopValue ought to copy the object's data into a new object in order to avoid aliasing bugs.

        Returns:
        V
        Throws:
        IllegalStateException - if called before seek.
        NoSuchElementException - if top element doesn't exist.

      • deepCopy

        SortedKeyValueIterator<K,​V> deepCopy​(IteratorEnvironment env)
        Creates a deep copy of this iterator as though seek had not yet been called. init should be called on an iterator before deepCopy is called. init should not need to be called on the copy that is returned by deepCopy; that is, when necessary init should be called in the deepCopy method on the iterator it returns. The behavior is unspecified if init is called after deepCopy either on the original or the copy. A proper implementation would call deepCopy on the source.
        Parameters:
        env - IteratorEnvironment environment in which iterator is being run, provided by Accumulo itself and is expected to be non-null.
        Returns:
        SortedKeyValueIterator a copy of this iterator (with the same source and settings).
        Throws:
        UnsupportedOperationException - if not supported.

      • isRunningLowOnMemory

        default boolean isRunningLowOnMemory()
        Returns true when running in a server process and the GarbageCollectionLogger determines that the server is running low on memory. This is useful for iterators that aggregate KV pairs or perform long running operations that create a lot of garbage. Server side iterators can override this method and return the value of IteratorEnvironment.isRunningLowOnMemory.
        Returns:
        true if running in server process and server is running low on memory
        Since:
        3.0.0