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Cassandra for Oracle DBA’s Part 14: Tombstones – Undo type structures

Undo like pointers, tombstones

Cassandra uses a log-structured storage engine. Because of this, deletes do not remove the rows and columns immediately and in-place. Instead, Cassandra writes a special marker, called a tombstone, indicating that a row, column, or range of columns was deleted. These tombstones are kept for at least the period of time defined by the gc_grace_seconds per-table setting. Only then a tombstone can be permanently discarded by compaction.

This scheme allows for very fast deletes (and writes in general), but it’s not free: aside from the obvious RAM/disk overhead of tombstones, you might have to pay a certain price when reading data back if you haven’t modelled your data well.

gc_grace_seconds - Kind of undo retention

 

tombstone_warn_threshold 

    (Default: 1000) The maximum number of tombstones a query can scan before warning.

 

tombstone_failure_threshold 

    (Default: 100000) The maximum number of tombstones a query can scan before aborting. 

October 1st, 2016 | Tags: , , , | Category: 12c Database, Cassandra

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