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From Shalom Sagges <>
Subject About Tombstones and TTLs
Date Mon, 19 Dec 2016 12:00:19 GMT
Hi Everyone,

I was reading a blog on TWCS by Alex Dejanovski from The Last Pickle (

When I got to the comments section, I didn't understand why setting
gc_grace_seconds to 0 will disable hints for the associated table:
*"It is a very good point that gc_grace_seconds shouldn't be lowered too
much as its impact on hinted handoff is not a well known fact, and using a
value of 0 will purely disable hints on the table."*

When I tried to read some more about deletes and TTLs, I got to a Datastax
stating the following:

*Cassandra allows you to set a default_time_to_live property for an entire
table. Columns and rows marked with regular TTLs are processed as described
above; but when a record exceeds the table-level TTL, Cassandra deletes it
immediately, without tombstoning or compaction.*

Which got me a bit more confused.
So I hope someone can shed some light on some questions I've got:

   - Why setting gc_grace_seconds=0 will disable hints for the table?
   - How can an expired TTL record be deleted by Cassandra without
   tombstoning or compaction? Aren't SSTables immutable files, and expired
   records are removed through compaction?
   - If I only use TTL for deletion, do I still need gc_grace_seconds to be
   bigger than 0?
   - If I only use TTL for deletion, but use updates as well, do I need
   gc_grace_seconds to be bigger than 0?

Sorry for all those questions, I'm just really confused from all the
TTL/tombstones subject (still a newbie).

Thanks a lot!

Shalom Sagges
T: +972-74-700-4035
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