changing compaction strategy

[Mike Torra <mt...@salesforce.com>]

I'm trying to change compaction strategy one node at a time. I'm using
jmxterm like this:

`echo 'set -b
org.apache.cassandra.db:type=ColumnFamilies,keyspace=my_ks,columnfamily=my_cf
CompactionParametersJson
\{"class":"TimeWindowCompactionStrategy","compaction_window_unit":"HOURS","compaction_window_size":"6"\}'
| java -jar jmxterm-1.0-alpha-4-uber.jar --url localhost:7199`

and I see this in the cassandra logs:

INFO  [RMI TCP Connection(37)-127.0.0.1] 2017-03-13 20:29:08,251
CompactionStrategyManager.java:841 - Switching local compaction strategy
from
CompactionParams{class=org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy,
options={max_threshold=32, min_threshold=4}} to
CompactionParams{class=org.apache.cassandra.db.compaction.TimeWindowCompactionStrategy,
options={min_threshold=4, max_threshold=32, compaction_window_unit=HOURS,
compaction_window_size=6}}}

After doing this, `nodetool compactionstats` shows 1 pending compaction,
but none running. Also, cqlsh describe shows the old compaction strategy
still. Am I missing a step?

Re: changing compaction strategy

[kurt greaves <ku...@instaclustr.com>]

The rogue pending task is likely a non-issue. If your jmx command went
through without errors and you got the log message you can assume it
worked. It won't show in the schema unless you run the ALTER statement
which affects the whole cluster.

If you were switching from STCS then you wouldn't expect any recompaction,
as SSTables will just be calculated to be in their relevant window. On the
other hand switching from LCS would generate many compactions.
​
The only way to really tell is to confirm SSTables are expiring as you
would expect them to, or verify that new SSTables are not being compacted
with older ones. You might need to wait for at least one time window to
pass to check this.

Re: changing compaction strategy

[Mike Torra <mt...@salesforce.com>]

Some more info:
- running C* 3.9
- I tried `nodetool flush` on the column family this change applies to, and
while it does seem to trigger compactions, there is still one pending that
won't seem to run
- I tried `nodetool compact` on the column family as well, with a similar
affect

Is there a way to tell when/if the local node has successfully updated the
compaction strategy? Looking at the sstable files, it seems like they are
still based on STCS but I don't know how to be sure.

Appreciate any tips or suggestions!

On Mon, Mar 13, 2017 at 5:30 PM, Mike Torra <mt...@salesforce.com> wrote:

> I'm trying to change compaction strategy one node at a time. I'm using
> jmxterm like this:
>
> `echo 'set -b org.apache.cassandra.db:type=ColumnFamilies,keyspace=my_ks,columnfamily=my_cf
> CompactionParametersJson \{"class":"TimeWindowCompactionStrategy",
> "compaction_window_unit":"HOURS","compaction_window_size":"6"\}' | java
> -jar jmxterm-1.0-alpha-4-uber.jar --url localhost:7199`
>
> and I see this in the cassandra logs:
>
> INFO  [RMI TCP Connection(37)-127.0.0.1] 2017-03-13 20:29:08,251
> CompactionStrategyManager.java:841 - Switching local compaction strategy
> from CompactionParams{class=org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy,
> options={max_threshold=32, min_threshold=4}} to CompactionParams{class=org.
> apache.cassandra.db.compaction.TimeWindowCompactionStrategy,
> options={min_threshold=4, max_threshold=32, compaction_window_unit=HOURS,
> compaction_window_size=6}}}
>
> After doing this, `nodetool compactionstats` shows 1 pending compaction,
> but none running. Also, cqlsh describe shows the old compaction strategy
> still. Am I missing a step?
>