public abstract class RowFilter extends WrappingIterator
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 and Description |
---|
RowFilter() |
Modifier and Type | Method and Description |
---|---|
abstract boolean |
acceptRow(SortedKeyValueIterator<Key,Value> rowIterator)
Implementation should return false to suppress a row.
|
SortedKeyValueIterator<Key,Value> |
deepCopy(IteratorEnvironment env)
Creates a deep copy of this iterator as though seek had not yet been called.
|
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.
|
getSource, getTopKey, getTopValue, setSource
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
enableYielding
public abstract boolean acceptRow(SortedKeyValueIterator<Key,Value> rowIterator) throws IOException
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.IOException
public void init(SortedKeyValueIterator<Key,Value> source, Map<String,String> options, IteratorEnvironment env) throws IOException
SortedKeyValueIterator
init
in interface SortedKeyValueIterator<Key,Value>
init
in class WrappingIterator
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.IOException
- unused.public SortedKeyValueIterator<Key,Value> deepCopy(IteratorEnvironment env)
SortedKeyValueIterator
deepCopy
in interface SortedKeyValueIterator<Key,Value>
deepCopy
in class WrappingIterator
env
- IteratorEnvironment environment in which iterator is being run.public boolean hasTop()
SortedKeyValueIterator
hasTop
in interface SortedKeyValueIterator<Key,Value>
hasTop
in class WrappingIterator
public void next() throws IOException
SortedKeyValueIterator
next
in interface SortedKeyValueIterator<Key,Value>
next
in class WrappingIterator
IOException
- if an I/O error occurs.public void seek(Range range, Collection<ByteSequence> columnFamilies, boolean inclusive) throws IOException
SortedKeyValueIterator
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.
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.seek
in interface SortedKeyValueIterator<Key,Value>
seek
in class WrappingIterator
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.IOException
- if an I/O error occurs.Copyright © 2011–2019 The Apache Software Foundation. All rights reserved.