[CASSANDRA-418] SSTable generation clash during compaction

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 0.4
• Severity: Normal
• Assignee: Jonathan Ellis
• Reporter: Sammy Yu

Authors

Jonathan Ellis

• Created: 03/Sep/09 01:51
• Updated: 16/Apr/19 09:33
• Resolved: 07/Sep/09 14:50

Description

We found that one of our node started getting timeouts for get_slice. Looking further we found that the CFS.ssTables_ references a SStable doesn't exist on the file system.

Walking down the log we see that the sstable in question 6038 is being compacted onto itself (in terms of filename file wise it is written to -tmp):
system.log.2009-09-01: INFO [MINOR-COMPACTION-POOL:1] 2009-09-01 23:50:07,553 ColumnFamilyStore.java (line 1067) Compacting
[/mnt/var/cassandra/data/Digg/FriendActions-6037-Data.db,/mnt/var/cassandra/data/Digg/FriendActions-6038-Data.db,/mnt/var/cassandra/data/Digg/
FriendActions-6040-Data.db,/mnt/var/cassandra/data/Digg/FriendActions-6042-Data.db]
system.log.2009-09-01: INFO [MINOR-COMPACTION-POOL:1] 2009-09-01 23:51:43,727 ColumnFamilyStore.java (line 1209) Compacted to
/mnt/var/cassandra/data/Digg/FriendActions-6038-Data.db. 0/1010269806 bytes for 9482/9373 keys read/written. Time: 96173ms.

It appears the generation number is generated by looking at the lowest number in the list of files to be compacted and adding 1. In this scenario it is 6037+1=6038.
The code in CFS.doFileCompaction will remove the key and add the key back and remove the key again, hence the error we were seeing.

Should the generation number be generated via another way or should we update doFileCompaction to be smarter?