org.apache.accumulo.core.client

Interface ScannerBase

All Superinterfaces:

Iterable<Map.Entry<Key,Value>>

All Known Subinterfaces:

BatchDeleter, BatchScanner, Scanner

All Known Implementing Classes:

ClientSideIteratorScanner, IsolatedScanner, MockBatchDeleter, MockBatchScanner, MockScanner, MockScannerBase, OfflineScanner, ScannerImpl, ScannerOptions, TabletServerBatchDeleter, TabletServerBatchReader

public interface ScannerBase
extends Iterable<Map.Entry<Key,Value>>

This class hosts configuration methods that are shared between different types of scanners.

Method Summary

Methods

Modifier and Type	Method and Description
void	addScanIterator(IteratorSetting cfg) Add a server-side scan iterator.
void	clearColumns() Clears the columns to be fetched (useful for resetting the scanner for reuse).
void	clearScanIterators() Clears scan iterators prior to returning a scanner to the pool.
void	close() Closes any underlying connections on the scanner
void	fetchColumn(IteratorSetting.Column column) Adds a column to the list of columns that will be fetch by this scanner.
void	fetchColumn(org.apache.hadoop.io.Text colFam, org.apache.hadoop.io.Text colQual) Adds a column to the list of columns that will be fetched by this scanner.
void	fetchColumnFamily(org.apache.hadoop.io.Text col) Adds a column family to the list of columns that will be fetched by this scanner.
Authorizations	getAuthorizations() Returns the authorizations that have been set on the scanner
long	getTimeout(TimeUnit timeUnit) Returns the setting for how long a scanner will automatically retry when a failure occurs.
Iterator<Map.Entry<Key,Value>>	iterator() Returns an iterator over an accumulo table.
void	removeScanIterator(String iteratorName) Remove an iterator from the list of iterators.
void	setTimeout(long timeOut, TimeUnit timeUnit) This setting determines how long a scanner will automatically retry when a failure occurs.
void	updateScanIteratorOption(String iteratorName, String key, String value) Update the options for an iterator.

Method Detail

addScanIterator

void addScanIterator(IteratorSetting cfg)

Add a server-side scan iterator.

Parameters:

cfg - fully specified scan-time iterator, including all options for the iterator. Any changes to the iterator setting after this call are not propagated to the stored iterator.

Throws:

IllegalArgumentException - if the setting conflicts with existing iterators

removeScanIterator

void removeScanIterator(String iteratorName)

Remove an iterator from the list of iterators.

Parameters:

iteratorName - nickname used for the iterator

updateScanIteratorOption

void updateScanIteratorOption(String iteratorName,
                            String key,
                            String value)

Update the options for an iterator. Note that this does not change the iterator options during a scan, it just replaces the given option on a configured iterator before a scan is started.

Parameters:

iteratorName - the name of the iterator to change

key - the name of the option

value - the new value for the named option

fetchColumnFamily

void fetchColumnFamily(org.apache.hadoop.io.Text col)

Adds a column family to the list of columns that will be fetched by this scanner. By default when no columns have been added the scanner fetches all columns. To fetch multiple column families call this function multiple times.

This can help limit which locality groups are read on the server side.

When used in conjunction with custom iterators, the set of column families fetched is passed to the top iterator's seek method. Custom iterators may change this set of column families when calling seek on their source.

Parameters:

col - the column family to be fetched

fetchColumn

void fetchColumn(org.apache.hadoop.io.Text colFam,
               org.apache.hadoop.io.Text colQual)

Adds a column to the list of columns that will be fetched by this scanner. The column is identified by family and qualifier. By default when no columns have been added the scanner fetches all columns.

WARNING. Using this method with custom iterators may have unexpected results. Iterators have control over which column families are fetched. However iterators have no control over which column qualifiers are fetched. When this method is called it activates a system iterator that only allows the requested family/qualifier pairs through. This low level filtering prevents custom iterators from requesting additional column families when calling seek.

For an example, assume fetchColumns(A, Q1) and fetchColumns(B,Q1) is called on a scanner and a custom iterator is configured. The families (A,B) will be passed to the seek method of the custom iterator. If the custom iterator seeks its source iterator using the families (A,B,C), it will never see any data from C because the system iterator filtering A:Q1 and B:Q1 will prevent the C family from getting through. ACCUMULO-3905 also has an example of the type of problem this method can cause.

tl;dr If using a custom iterator with a seek method that adds column families, then may want to avoid using this method.

Parameters:

colFam - the column family of the column to be fetched

colQual - the column qualifier of the column to be fetched

fetchColumn

void fetchColumn(IteratorSetting.Column column)

Adds a column to the list of columns that will be fetch by this scanner.

Parameters:

column - the IteratorSetting.Column to fetch

Since:

1.7.0

clearColumns

void clearColumns()

Clears the columns to be fetched (useful for resetting the scanner for reuse). Once cleared, the scanner will fetch all columns.

clearScanIterators

void clearScanIterators()

Clears scan iterators prior to returning a scanner to the pool.

iterator

Iterator<Map.Entry<Key,Value>> iterator()

Returns an iterator over an accumulo table. This iterator uses the options that are currently set for its lifetime, so setting options will have no effect on existing iterators.

Keys returned by the iterator are not guaranteed to be in sorted order.

Specified by:

iterator in interface Iterable<Map.Entry<Key,Value>>

Returns:

an iterator over Key,Value pairs which meet the restrictions set on the scanner

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.

Parameters:

timeOut - the length of the timeout

timeUnit - the units of the timeout

Since:

1.5.0

getTimeout

long getTimeout(TimeUnit timeUnit)

Returns the setting for how long a scanner will automatically retry when a failure occurs.

Returns:

the timeout configured for this scanner

Since:

1.5.0

close

void close()

Closes any underlying connections on the scanner

Since:

1.5.0

getAuthorizations

Authorizations getAuthorizations()

Returns the authorizations that have been set on the scanner

Returns:

The authorizations set on the scanner instance

Since:

1.7.0