[CASSANDRA-8140] Compaction has no effects

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Not A Problem
• Severity: Normal
• Since Version: 2.1.0
• Assignee: Marcus Eriksson
• Reporter: Davide

Authors

Marcus Eriksson

• Created: 19/Oct/14 00:33
• Updated: 16/Apr/19 09:31
• Resolved: 20/Oct/14 18:19

Description

Hi there,

I'm on cassandra 2.1 since then I figured out that in some circumstances (I can't find a way to reproduce them constantly) minor compactions and full compactions had no effects.

We are on a cluster composed of 5 nodes with around 500gb of data, no deletions around 1.5k updates/s and same on reads.

After a repair I saw that a couple of nodes were `slow`, I investigate further and I found that on these two nodes the number of sstable were around 20.000+ ! We use STC.

So with node tool I triggered a full compaction, It took less than I minute (with nothing in the logs) and of course the number of sstable didn't go down.

Then I drained the node, and I ran again with `nodetool compact`, at that point the number of sstables went down to less than 10.

I tough was a strange spot problem. However after a week I noticed that one node had ~100 sstabels where others just 8-10.

I ran again the compaction (It last less than a minute with nothing in logs) and didn't change anything. I drained it and restarted then compacted and took several hours to get it back close to 2/3 sstables.

What could be? We never incurred this behavior before.

Here informations about the table:

CREATE TABLE xyz (
    ppk text PRIMARY KEY,
   .. ten more columns...
) WITH bloom_filter_fp_chance = 0.01
    AND caching = '{"keys":"ALL", "rows_per_partition":"NONE"}'
    AND comment = ''
    AND compaction = {'min_threshold': '4', 'cold_reads_to_omit': '0.0', 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', 'max_threshold': '32'}
    AND compression = {'sstable_compression': 'org.apache.cassandra.io.compress.SnappyCompressor'}
    AND dclocal_read_repair_chance = 0.0
    AND default_time_to_live = 0
    AND gc_grace_seconds = 864000
    AND max_index_interval = 2048
    AND memtable_flush_period_in_ms = 0
    AND min_index_interval = 128
    AND read_repair_chance = 0.0
    AND speculative_retry = '99.0PERCENTILE';

Here the current cf stats:

		SSTable count: 11
		Space used (live), bytes: 118007220865
		Space used (total), bytes: 118007220865
		Space used by snapshots (total), bytes: 170591332257
		SSTable Compression Ratio: 0.3643916626015517
		Memtable cell count: 920306
		Memtable data size, bytes: 70034097
		Memtable switch count: 25
		Local read count: 5358772
		Local read latency: 54.621 ms
		Local write count: 4715106
		Local write latency: 0.069 ms
		Pending flushes: 0
		Bloom filter false positives: 53757
		Bloom filter false ratio: 0.04103
		Bloom filter space used, bytes: 220634056
		Compacted partition minimum bytes: 18
		Compacted partition maximum bytes: 61214
		Compacted partition mean bytes: 1935
		Average live cells per slice (last five minutes): 0.8139232271871242
		Average tombstones per slice (last five minutes): 0.5493417148555677

Is there anything else that I can provide?

Thanks!
DD