I can think of following features to solve
1. If you know the time period of after how long data should be removed then
use TTL feature2. Use Time Series to model the data and use inverted index to
query the data by time period? Naidu Saladi
On Tuesday, November 24, 2015 6:49 AM, Jack Krupansky
<[email protected]> wrote:
How often is sometimes - closer to 20% of the batches or 2%?
How are you querying batches, both current and older ones?
As always, your queries should drive your data models.
If deleting a batch is very infrequent, maybe best to not do it and simply have
logic in the app to ignore deleted batches - if your queries would reference
them at all.
What reasons would you have to delete a batch? Depending on the nature of the
reason there may be an alternative.
Make sure your cluster is adequately provisioned so that these expensive
operations can occur in parallel to reduce their time and resources per node.
Do all batches eventually get aged and deleted or are you expecting that most
batches will live for many years to come? Have you planned for how you will
grow the cluster over time?
Maybe bite the bullet and use a background process to delete a batch if
deletion is competing too heavily with query access - if they really need to be
deleted at all.
Number of keyspaces - and/or tables - should be limited to "low hundreds", and
even then you are limited by RAM and CPU of each node. If a keyspace has 14
tables, then 250/14 = 20 would be a recommended upper limit for number of key
spaces. Even if your total number of tables was under 300 or even 200, you
would need to do a proof of concept implementation to verify that your specific
data works well on your specific hardware.
-- Jack Krupansky
On Tue, Nov 24, 2015 at 5:05 AM, Jonathan Ballet <[email protected]> wrote:
Hi,
we are running an application which produces every night a batch with several
hundreds of Gigabytes of data. Once a batch has been computed, it is never
modified (nor updates nor deletes), we just keep producing new batches every
day.
Now, we are *sometimes* interested to remove a complete specific batch
altogether. At the moment, we are accumulating all these data into only one
keyspace which has a batch ID column in all our tables which is also part of
the primary key. A sample table looks similar to this:
CREATE TABLE computation_results (
batch_id int,
id1 int,
id2 int,
value double,
PRIMARY KEY ((batch_id, id1), id2)
) WITH CLUSTERING ORDER BY (id2 ASC);
But we found out it is very difficult to remove a specific batch as we need to
know all the IDs to delete the entries and it's both time and resource
consuming (ie. it takes a long time and I'm not sure it's going to scale at
all.)
So, we are currently looking into having each of our batches in a keyspace of
their own so removing a batch is merely equivalent to delete a keyspace.
Potentially, it means we will end up having several hundreds of keyspaces in
one cluster, although most of the time only the very last one will be used (we
might still want to access the older ones, but that would be a very seldom
use-case.) At the moment, the keyspace has about 14 tables and is probably not
going to evolve much.
Are there any counter-indications of using lot of keyspaces (300+) into one
Cassandra cluster?
Are there any good practices that we should follow?
After reading the "Anti-patterns in Cassandra > Too many keyspaces or tables",
does it mean we should plan ahead to already split our keyspace among several
clusters?
Finally, would there be any other way to achieve what we want to do?
Thanks for your help!
Jonathan
