Cassandra handles this by using a different design, you don't append anything. You use the fact that in Cassandra you have dynamic columns and you make a new column every time you want to put more data in. Then when you do finally need to read the data out you read out a slice of columns, not just one column.
-Jeremiah -----Original Message----- From: Marcus Bointon [mailto:mar...@synchromedia.co.uk] Sent: Tuesday, May 31, 2011 2:23 PM To: user@cassandra.apache.org Subject: Appending to fields I'm wondering how cassandra implements appending values to fields. Since (so the docs tell me) there's not really any such thing such thing as an update in Cassandra, I wonder if it falls into the same trap as MySQL does. With a query like "update x set y = concat(y, 'a') where id = 1", mysql reads the entire value of y, appends the data, then writes the whole thing back, which unfortunately is an O(n^2) operation. The situation I'm doing this in involves what amount to log files on hundreds of thousands of items, many of which might need updating at once, so they're all simple appends, but it becomes unusably slow very quickly. In MySQL it's just a plain bug as it could optimise this by appending data at a known offset and then bumping up the field length counter, which is back in at least O(n) territory. Does cassandra's design avoid this problem? Marcus
