org.apache.accumulo.core.client

Interface BatchScanner

All Superinterfaces:

Iterable<Map.Entry<Key,Value>>, ScannerBase

All Known Implementing Classes:

MockBatchDeleter, MockBatchScanner

public interface BatchScanner
extends ScannerBase

In exchange for possibly returning scanned entries out of order, BatchScanner implementations may scan an Accumulo table more efficiently by

• Looking up multiple ranges in parallel. Parallelism is constrained by the number of threads available to the BatchScanner, set in its constructor.
• Breaking up large ranges into subranges. Often the number and boundaries of subranges are determined by a table's split points.
• Combining multiple ranges into a single RPC call to a tablet server.

The above techniques lead to better performance than a Scanner in use cases such as

• Retrieving many small ranges
• Scanning a large range that returns many entries
• Running server-side iterators that perform computation, even if few entries are returned from the scan itself

To re-emphasize, only use a BatchScanner when you do not care whether returned data is in sorted order. Use a Scanner instead when sorted order is important.

A BatchScanner instance will use no more threads than provided in the construction of the BatchScanner implementation. Multiple invocations of iterator() will all share the same resources of the instance. A new BatchScanner instance should be created to use allocate additional threads.

Method Summary

Modifier and Type	Method and Description
void	close() Closes any underlying connections on the scanner
void	setRanges(Collection<Range> ranges) Allows scanning over multiple ranges efficiently.
void	setTimeout(long timeout, TimeUnit timeUnit) This setting determines how long a scanner will automatically retry when a failure occurs.

Methods inherited from interface org.apache.accumulo.core.client.ScannerBase

addScanIterator, clearColumns, clearScanIterators, fetchColumn, fetchColumn, fetchColumnFamily, getAuthorizations, getTimeout, iterator, removeScanIterator, updateScanIteratorOption

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Method Detail

setRanges

void setRanges(Collection<Range> ranges)

Allows scanning over multiple ranges efficiently.

Parameters:

ranges - specifies the non-overlapping ranges to query

close

void close()

Description copied from interface: ScannerBase

Closes any underlying connections on the scanner

Specified by:

close in interface ScannerBase

setTimeout

void setTimeout(long timeout,
                TimeUnit timeUnit)

This setting determines how long a scanner will automatically retry when a failure occurs. By default, a scanner will retry forever.

Setting the timeout to zero (with any time unit) or Long.MAX_VALUE (with TimeUnit.MILLISECONDS) means no timeout.

The batch scanner will accomplish as much work as possible before throwing an exception. BatchScanner iterators will throw a TimedOutException when all needed servers timeout.

Specified by:

setTimeout in interface ScannerBase

Parameters:

timeout - the length of the timeout

timeUnit - the units of the timeout