hi,
i've been looking at the model below from Ed Anuff's presentation at
Cassandra CF (http://www.slideshare.net/edanuff/indexing-in-cassandra).
Couple of questions:
1) Isn't there still the chance that two concurrent updates may end up
with the index containing two entries for the given user, only one of
which would be match the actual value in the Users cf?
2) What happens if your batch fails partway through the update? If i
understand correctly there are no guarantees about ordering when a batch
is executed, so isn't it possible that eg the previous
value entries in Users_Index_Entries may have been deleted, and then the
batch fails before the entries in Indexes are deleted, ie the mechanism
has 'lost' those values? I assume this can be addressed
by not deleting the old entries until the batch has succeeded (ie put
the previous entry deletion into a separate, subsequent batch). this at
least lets you retry at a later time.
perhaps i'm missing something?
SELECT {"location"}..{"location", *}
FROM Users_Index_Entries WHERE KEY = <user_key>;
BEGIN BATCH
DELETE {"location", ts1}, {"location", ts2}, ...
FROM Users_Index_Entries WHERE KEY = <user_key>;
DELETE {<value1>, <user_key>, ts1}, {<value2>, <user_key>, ts2}, ...
FROM Indexes WHERE KEY = "Users_By_Location";
UPDATE Users_Index_Entries SET {"location", ts3} = <value3>
WHERE KEY=<user_key>;
UPDATE Indexes SET {<value3>, <user_key>, ts3) = null
WHERE KEY = "Users_By_Location";
UPDATE Users SET location = <value3>
WHERE KEY = <user_key>;
APPLY BATCH
