- All Implemented Interfaces:
public abstract class RowFilter extends WrappingIteratorThis 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
Scannerrow 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.
Constructors Constructor Description
All Methods Instance Methods Abstract Methods Concrete Methods Modifier and Type Method Description
acceptRow(SortedKeyValueIterator<Key,Value> rowIterator)Implementation should return false to suppress a row.
deepCopy(IteratorEnvironment env)Creates a deep copy of this iterator as though seek had not yet been called.
hasTop()Returns true if the iterator has more elements.
init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env)Initializes the iterator.
next()Advances to the next K,V pair.
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
getSource, getTopKey, getTopValue, setSource
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
public abstract boolean acceptRow(SortedKeyValueIterator<Key,Value> rowIterator) throws IOExceptionImplementation should return false to suppress a row.
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.
- false if a row should be suppressed, otherwise true.
public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) throws IOExceptionInitializes the iterator. Data should not be read from the source in this method.
- Specified by:
SortedKeyValueIteratorsource to read data from.
Mapmap of string option names to option values.
IteratorEnvironmentenvironment in which iterator is being run.
public SortedKeyValueIterator<Key,Value> 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.
public 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.
public void next() throws IOExceptionAdvances 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.
public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive) throws IOExceptionSeeks 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<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.
columnFamiliesis 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
columnFamiliesis properly set to the minimum required column families to ensure that data from separate locality groups is not inadvertently read.
- Specified by:
Rangeof keys to iterate over.
Collectionof column families to include or exclude.
booleanthat indicates whether to include (true) or exclude (false) column families.
IOException- if an I/O error occurs.