Hi Ben,
Looks like you're on the right track. Iterator priorities are a little
obtuse at first glance; you probably want to change the 1 to 15 (we can
touch on the "why" later).
As far as Iterators/Filters that you should feel comfortable using,
check out:
https://github.com/apache/accumulo/tree/master/core/src/main/java/org/apache/accumulo/core/iterators/user
The "system" package are not meant for public consumption (and often are
used to implement internal functionality). This is probably why you're
having a hard time figuring out how to use it.
Don't miss the methods on Scanner: fetchColumnFamily(Text),
fetchColumn(Text, Text), and fetchColumn(Column). These are how you can
easily do column family or column family + qualifier filtering.
For example, if you wanted to filter on the column family "foo" and the
column qualifier "bar":
```
Scanner scan = connector.createScanner("table", auths);
scan.fetchColumn(new Text("foo"), new Text("bar"));
RowIterator rowIterator = new RowIterator(scan);
while (...) { ... }
```
The fetch*() methods are also accumulative. If you want to fetch
multiple cf's (or cf+cq pairs), you can invoke the method multiple times.
Ben Craig wrote:
Hey Guys I'm new to Accumulo and trying to learn how to query data. I
think I've got the basics down like:
//create a scanner
Scanner scan = connector.createScanner( "table", auths );
//create a filter
IteratorSetting itr1 = new IteratorSetting( 1, "TimeFilter",
AgeOffFilter.class );
itr1.addOption( TTL, Long.toString( DEFAULT_QUERY_TIME ) );
scan.addScanIterator( itr1 );
//iterate over the resulting rows
RowIterator rowIterator = new RowIterator( scan );
while ( rowIterator.hasNext() )
{
}
I've been playing around with some of the built in filters and have been
able to apply multiple filters on top of each other. Some of the
filters I'm having issues with where they take a complex java object and
not just option<String,String>
For example ColumnQualifierFilter.java
<https://github.com/apache/accumulo/blob/master/core/src/main/java/org/apache/accumulo/core/iterators/system/ColumnQualifierFilter.java>
When we use Iterator Settings the class is implicitly created but if I
want to use the ColumnQualifierFilter I need to create one and pass it a
set of columns. I've been playing around with it for a while and havn't
been able to learn how to use it properly.
The constructor takes a sorted key value iterator. How do I get this
sorted key value iterator? Do I start with a scanner or do you start
with another type of scanner? Do I just make one?
new ArrayList<SortedKeyValueIterator<Key,Value>>(); ? And the data goes
into it?
I've read through this Accumulo
<http://shop.oreilly.com/product/0636920032304.do> book but it just
shows how you can use the Scanner/Iterator Settings to query.
If anyone has any suggestions / documentation / examples it be much
appreciated.
Thanks,
Ben
