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

java.lang.Object
  extended by org.apache.accumulo.core.iterators.WrappingIterator
      extended by org.apache.accumulo.core.iterators.user.RowFilter
All Implemented Interfaces:
SortedKeyValueIterator<Key,Value>

public abstract class RowFilter
extends WrappingIterator

This iterator makes it easy to select rows that meet a given criteria. Its an alternative to the WholeRowIterator. There are a few things to consider when deciding which one to use. First the WholeRowIterator requires that the row fit in memory and that the entire row is read before a decision is made. This iterator has neither requirement, it allows seeking within a row to avoid reading the entire row to make a decision. So even if your rows fit into memory, this extending this iterator may be better choice because you can seek. Second the WholeRowIterator is currently the only way to achieve row isolation with the BatchScanner. With the normal Scanner row isolation can be enabled and this Iterator may be used. Third the row acceptance test will be executed every time this Iterator is seeked. If the row is large, then the row will fetched in batches of key/values. As each batch is fetched the test may be re-executed because the iterator stack is reseeked for each batch. The batch size may be increased to reduce the number of times the test is executed. With the normal Scanner, if isolation is enabled then it will read an entire row w/o seeking this iterator.


Constructor Summary
RowFilter()
           
 
Method Summary
abstract  boolean acceptRow(SortedKeyValueIterator<Key,Value> rowIterator)
          Implementation should return false to suppress a row.
 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.
 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, setSource
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

RowFilter

public RowFilter()
Method Detail

acceptRow

public abstract boolean acceptRow(SortedKeyValueIterator<Key,Value> rowIterator)
                           throws IOException
Implementation should return false to suppress a row.

Parameters:
rowIterator - - An iterator over the row. This iterator is confined to the row. Seeking past the end of the row will return no data. Seeking before the row will always set top to the first column in the current row. By default this iterator will only see the columns the parent was seeked with. To see more columns reseek this iterator with those columns.
Returns:
false if a row should be suppressed, otherwise true.
Throws:
IOException

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>
Overrides:
init in class WrappingIterator
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.

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>
Overrides:
hasTop in class WrappingIterator
Returns:
true if the iterator has more elements.

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.

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.

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.


Copyright © 2012 The Apache Software Foundation. All Rights Reserved.