org.apache.accumulo.core.iterators.user
Class RowEncodingIterator

java.lang.Object
  org.apache.accumulo.core.iterators.user.RowEncodingIterator

All Implemented Interfaces:

SortedKeyValueIterator<Key,Value>

Direct Known Subclasses:

WholeRowIterator

public abstract class RowEncodingIterator
extends Object
implements SortedKeyValueIterator<Key,Value>

The RowEncodingIterator is designed to provide row-isolation so that queries see mutations as atomic. It does so by encapsulating an entire row of key/value pairs into a single key/value pair, which is returned through the client as an atomic operation. This is an abstract class, allowing the user to implement rowEncoder and rowDecoder such that the columns and values of a given row may be encoded in a format best suited to the client.

For an example implementation, see WholeRowIterator.

One caveat is that when seeking in the WholeRowIterator using a range that starts at a non-inclusive first key in a row, (e.g. seek(new Range(new Key(new Text("row")),false,...),...)) this iterator will skip to the next row. This is done in order to prevent repeated scanning of the same row when system automatically creates ranges of that form, which happens in the case of the client calling continueScan, or in the case of the tablet server continuing a scan after swapping out sources.

To regain the original key/value pairs of the row, call the rowDecoder function on the key/value pair that this iterator returned.

See Also:

RowFilter

Field Summary

protected SortedKeyValueIterator<Key,Value>

sourceIter

Constructor Summary

RowEncodingIterator()

Method Summary

abstract SortedKeyValueIterator<Key,Value>	deepCopy(IteratorEnvironment env) Implement deepCopy.
protected boolean	filter(org.apache.hadoop.io.Text currentRow, List<Key> keys, List<Value> values)
Key	getTopKey() Returns top key.
Value	getTopValue() Returns top value.
boolean	hasTop() Returns true if the iterator has more elements.
void	init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) Initializes the iterator.
void	next() Advances to the next K,V pair.
abstract SortedMap<Key,Value>	rowDecoder(Key rowKey, Value rowValue) Given a value generated by the rowEncoder implementation, recreate the original Key, Value pairs.
abstract Value	rowEncoder(List<Key> keys, List<Value> values) Take a stream of keys and values.
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 java.lang.Object

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

Field Detail

sourceIter

protected SortedKeyValueIterator<Key,Value> sourceIter

Constructor Detail

RowEncodingIterator

public RowEncodingIterator()

Method Detail

rowDecoder

public abstract SortedMap<Key,Value> rowDecoder(Key rowKey,
                                                Value rowValue)
                                         throws IOException

Given a value generated by the rowEncoder implementation, recreate the original Key, Value pairs.

Throws:

IOException

rowEncoder

public abstract Value rowEncoder(List<Key> keys,
                                 List<Value> values)
                          throws IOException

Take a stream of keys and values. Return values in the same order encoded such that all portions of the key (except for the row value) and the original value are encoded in some way.

Throws:

IOException

deepCopy

public abstract SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)

Implement deepCopy. Ensure sourceIter is copied appropriately.

Specified by:

deepCopy in interface SortedKeyValueIterator<Key,Value>

Parameters:

env - IteratorEnvironment environment in which iterator is being run.

Returns:

SortedKeyValueIterator a copy of this iterator (with the same source and settings).

filter

protected boolean filter(org.apache.hadoop.io.Text currentRow,
                         List<Key> keys,
                         List<Value> values)

Parameters:

currentRow - All keys have this in their row portion (do not modify!).

keys - One key for each key in the row, ordered as they are given by the source iterator (do not modify!).

values - One value for each key in keys, ordered to correspond to the ordering in keys (do not modify!).

Returns:

true if we want to keep the row, false if we want to skip it

getTopKey

public Key getTopKey()

Description copied from interface: SortedKeyValueIterator

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.

Specified by:

getTopKey in interface SortedKeyValueIterator<Key,Value>

Returns:

K

getTopValue

public Value getTopValue()

Description copied from interface: SortedKeyValueIterator

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

Specified by:

getTopValue in interface SortedKeyValueIterator<Key,Value>

Returns:

V

hasTop

public boolean hasTop()

Description copied from interface: SortedKeyValueIterator

Returns true if the iterator has more elements.

Specified by:

hasTop in interface SortedKeyValueIterator<Key,Value>

Returns:

true if the iterator has more elements.

init

public void init(SortedKeyValueIterator<Key,Value> source,
                 Map<String,String> options,
                 IteratorEnvironment env)
          throws IOException

Description copied from interface: SortedKeyValueIterator

Initializes the iterator. Data should not be read from the source in this method.

Specified by:

init in interface SortedKeyValueIterator<Key,Value>

Parameters:

source - SortedKeyValueIterator source to read data from.

options - Map map of string option names to option values.

env - IteratorEnvironment environment in which iterator is being run.

Throws:

IOException - unused.

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>

Throws:

IOException - if an I/O error occurs.

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>

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.