org.apache.accumulo.core.iterators

Class SkippingIterator

java.lang.Object

org.apache.accumulo.core.iterators.WrappingIterator

org.apache.accumulo.core.iterators.SkippingIterator

All Implemented Interfaces:

SortedKeyValueIterator<Key,Value>

Direct Known Subclasses:

ColumnFamilySkippingIterator, FirstEntryInRowIterator

public abstract class SkippingIterator
extends WrappingIterator

Every call to next() and seek(Range, Collection, boolean) calls the parent's implementation and then calls the implementation's consume(). This provides a cleaner way for implementers to write code that will read one to many key-value pairs, as opposed to returning every key-value pair seen.

Constructor Summary

Constructors

Constructor and Description
SkippingIterator()

Method Summary

Methods

Modifier and Type	Method and Description
protected abstract void	consume()
void	next() Advances to the next K,V pair.
void	seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive) Seeks to the first key in the Range, restricting the resulting K,V pairs to those with the specified columns.

Methods inherited from class org.apache.accumulo.core.iterators.WrappingIterator

deepCopy, getSource, getTopKey, getTopValue, hasTop, init, setSource

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SkippingIterator

public SkippingIterator()

Method Detail

next

public void next()
          throws IOException

Description copied from interface: SortedKeyValueIterator

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.

Specified by:

next in interface SortedKeyValueIterator<Key,Value>

Overrides:

next in class WrappingIterator

Throws:

IOException - if an I/O error occurs.

consume

protected abstract void consume()
                         throws IOException

Throws:

IOException

seek

public void seek(Range range,
        Collection<ByteSequence> columnFamilies,
        boolean inclusive)
          throws IOException

Description copied from interface: SortedKeyValueIterator

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 SortedKeyValueIterator.init(org.apache.accumulo.core.iterators.SortedKeyValueIterator, java.util.Map, 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.

Specified by:

seek in interface SortedKeyValueIterator<Key,Value>

Overrides:

seek in class WrappingIterator

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.