Sorry, my code was a little off. It should have been
Scan scan = new Scan(calculateStartRowKey(targetAccount),
calculateEndRowKey(targetAccount));
Where my row key is formed from <account><reverse timestamp>
So, the scanner would match all the rows for this account, and return
them most recent first.
Iterator<Result> it = scanner.iterator();
But if I stop doing this...
Result result = it.next();
Will that be efficient? Will the scanner potentially matching all rows
for the account be a problem?
P
On 3/2/12 4:49 PM, Ian Varley wrote:
Yes, you do have to worry about efficiency. If your rows aren't ordered in the
table (by rowkey) according to the update date, the server will be having to
scan the entire table. Your filter will enable it to not send all of those
results to the client, but it's still having to read them from disk and merge
them with the rows in memory. It will likely not even be possible for a big
table (and, if it's not a *big* table, it probably shouldn't be in HBase).
The fundamental thing to note here is that there's no "magic": HBase stores
records sorted in exactly one order; if what you want isn't able to be efficiently found
according to that ordering, then you'll be scanning the whole table. Relational DBs do
that too, but they also have indexes that let you get at things quickly in some other
sort order.
Ian
On Mar 2, 2012, at 3:42 PM, Peter Wolf wrote:
Ah ha! So the row key orders the results, I just do an unbounded Scan,
and stop after N iterations.
Like this...
Scan scan = new Scan();
Filter filter = new SingleColumnValueFilter(...);
scan.setFilter(filter);
ResultScanner scanner = hTable.getScanner(scan);
Iterator<Result> it = scanner.iterator();
for ( int i=0; i<1000&& it.hasNext(); i++) {
Result result = it.next();
... do stuff with result...
}
Do I have to worry about efficiency? Is the Server madly retrieving
rows, in the background, that the Client will never use?
Thanks
P
On 3/2/12 4:31 PM, Doug Meil wrote:
Hi there-
Take a look at this section of the book...
http://hbase.apache.org/book.html#reverse.timestamp
On 3/2/12 4:02 PM, "Peter Wolf"<[email protected]<mailto:[email protected]>>
wrote:
Hello all,
I want to retrieve the most recent N rows from a table, with some column
qualifiers.
I can't find a Filter, or anything obvious in my books, or via Google.
What is the idiom for doing this?
Thanks
Peter
