Re: Time-to-live on SuperColumns

[Andy Burgess]

In reply to my own question, I'm clearly talking nonsense. SuperColumns are cleared out when empty (because really, what's the difference from the client point of view?) and so setting TTL at the Column level is plainly good enough. This was actually solved by dropping GCGraceSeconds right down to something very small - probably not appropriate for a production environment, but at least I know that the data will be deleted properly. In a related question - is there any way to trigger a deletion of sstables which have already been compacted (SSTABLE-CLEANUP-TIMER thread)? These could potentially take up a lot of disk space, and are surely no longer being used. What triggers Cassandra to perform these deletions, and can I do it manually? Thanks, Andy. On 19/01/11 11:36, Andy Burgess wrote: Hi, I'm trying to use the time-to-live functionality, which I've patched into Cassandra 0.6.6. My problem is that my sstables are not emptying. When my data expires, they do reduce in size, but only by a fraction of what I expected. I've come to realise that this must be because I've set the TTL on my Columns, but actually, I need the SuperColumns to expire too - I believe that my sstables remain large because I (probably) have a lot of empty SuperColumns. Unfortunately, I can't see a way to set a TTL on a SuperColumn. Does anyone have any suggestions for what I can do here? Actually, I've also just been playing with a few tests of "manually" deleting a SuperColumn, rather than using TTL - i.e. using Hector's Deletion with setSuper_column. Whilst this appears to work as far as making the data unavailable to the client is concerned, it only appears to reduce sstable size by about three quarters. This is in the case where I know that the sstable contains only my test inserts, which I have completely deleted. Why doesn't the sstable reduce in size to (almost) nothing? Thanks, Andy. WorldPay (UK) Limited, Company No. 07316500. Registered Office: 55 Mansell Street, London E1 8AN Authorised and regulated by the Financial Services Authority. ‘WorldPay Group’ means WorldPay (UK) Limited and its affiliates from time to time. A reference to an “affiliate” means any Subsidiary Undertaking, any Parent Undertaking and any Subsidiary Undertaking of any such Parent Undertaking and reference to a “Parent Undertaking” or a “Subsidiary Undertaking” is to be construed in accordance with section 1162 of the Companies Act 2006, as amended. DISCLAIMER: This email and any files transmitted with it, including replies and forwarded copies (which may contain alterations) subsequently transmitted from the WorldPay Group, are confidential and solely for the use of the intended recipient. If you are not the intended recipient (or authorised to receive for the intended recipient), you have received this email in error and any review, use, distribution or disclosure of its content is strictly prohibited. If you have received this email in error please notify the sender immediately by replying to this message. Please then delete this email and destroy any copies of it. Messages sent to and from the WorldPay Group may be monitored to ensure compliance with internal policies and to protect our business. Emails are not necessarily secure. The WorldPay Group does not accept responsibility for changes made to this message after it was sent. Please note that neither the WorldPay Group nor the sender accepts any responsibility for viruses and it is the responsibility of the recipient to ensure that the onward transmission, opening or use of this message and any attachments will not adversely affect its systems or data. Anyone who communicates with us by email is taken to accept these risks. Opinions, conclusions and other information contained in this message that do not relate to the official business of the WorldPay Group shall not be understood as endorsed or given by it. -- Andy Burgess Principal Development Engineer Application Delivery WorldPay Ltd. 270-289 Science Park, Milton Road Cambridge, CB4 0WE, United Kingdom (Depot Code: 024) Office: +44 (0)1223 706 779| Mobile: +44 (0)7909 534 940 andy.burg...@worldpay.com

WorldPay (UK) Limited, Company No. 07316500. Registered Office: 55 Mansell 
Street, London E1 8AN

Authorised and regulated by the Financial Services Authority.

‘WorldPay Group’ means WorldPay (UK) Limited and its affiliates from time to 
time.  A reference to an “affiliate” means any Subsidiary Undertaking, any 
Parent Undertaking and any Subsidiary Undertaking of any such Parent 
Undertaking and reference to a “Parent Undertaking” or a “Subsidiary 
Undertaking” is to be construed in accordance with section 1162 of the 
Companies Act 2006, as amended.

DISCLAIMER: This email and any files transmitted with it, including replies and 
forwarded copies (which may contain alterations) subsequently transmitted from 
the WorldPay Group, are confidential and solely for the use of the intended 
recipient. If you are not the intended recipient (or authorised to receive for 
the intended recipient), you have received this email in error and any review, 
use, distribution or disclosure of its content is strictly prohibited. If you 
have received this email in error please notify the sender immediately by 
replying to this message. Please then delete this email and destroy any copies 
of it.

Messages sent to and from the WorldPay Group may be monitored to ensure 
compliance with internal policies and to protect our business.  Emails are not 
necessarily secure.  The WorldPay Group does not accept responsibility for 
changes made to this message after it was sent. Please note that neither the 
WorldPay Group nor the sender accepts any responsibility for viruses and it is 
the responsibility of the recipient to ensure that the onward transmission, 
opening or use of this message and any attachments will not adversely affect 
its systems or data. Anyone who communicates with us by email is taken to 
accept these risks. Opinions, conclusions and other information contained in 
this message that do not relate to the official business of the WorldPay Group 
shall not be understood as endorsed or given by it.