Hi, Any improvement on this?
2 ideas coming to my mind: Yes, we are storing timeseries-like binary blobs where data is heavily > TTLed (essentially the entire column family is incrementally refreshed with > completely new data every few days) This looks to me like a good fit for TWCS (https://github.com/jeffjirsa/twcs), Jeff would know that better than I ;-), or DTCS developed by Marcus for Spotify back then ( https://labs.spotify.com/2014/12/18/date-tiered-compaction/). This way you would alleviate substancially compactions need as all the expired SSTables would be removed with no compaction. The second one is mainstream it is present in Cassandra, TWCS is not, but has been built to work around some DTCS issues and is heavy usage and maintained by Jeff for now. I drain the node, the compactions completely stop after a few minutes > (like they would normally do on another "healthy" node), it's just the > "pending tasks" counter that stays high, and messes up my metrics in > OpsCenter Maybe is there a compaction stuck there. It happened to me in the past. Checking sstables considered in remaining compaction after you drained can be helpful to troubleshoot. Run: "echo 'SELECT * FROM system.compactions_in_progress;' | cqlsh" and try to find that you indeed have compactions pending (there were some issue with the pending compaction metric recently and from the 'inputs' table look for some sstable(s) that is present in all the operation (on multiple sstables being used in many compactions processes. When I had the issue of a sstable blocking the compactions, it was very obvious. You can also try: " echo 'TRUNCATE system.compactions_in_progress;' | cqlsh" and restart the node, see what happen. If you spot some sstable messing in some node, you can try removing the sstable and repairing the table (one node at the time). C*heers, ----------------------- Alain Rodriguez - al...@thelastpickle.com France The Last Pickle - Apache Cassandra Consulting http://www.thelastpickle.com 2016-03-22 6:02 GMT+01:00 Gianluca Borello <gianl...@sysdig.com>: > Thank you for your reply. To address your points: > > - We are not running repairs > > - Yes, we are storing timeseries-like binary blobs where data is heavily > TTLed (essentially the entire column family is incrementally refreshed with > completely new data every few days) > > - I have tried with increasing compactors and even putting the compaction > throughput to unlimited, and nothing changes. Again, the key here to > remember is that if I drain the node, the compactions completely stop after > a few minutes (like they would normally do on another "healthy" node), it's > just the "pending tasks" counter that stays high, and messes up my metrics > in OpsCenter > > - As another data point: even if I increase the number of resources > allocated to compactions, I can pretty much measure that the disk I/O > generated by Cassandra is essentially the same as the other nodes that have > no pending compactions. In other words, it really seems like that number of > estimated pending compactions is somehow bogus > > Thanks > > On Mon, Mar 21, 2016 at 9:45 PM, Fabrice Facorat < > fabrice.faco...@gmail.com> wrote: > >> Are you running repairs ? >> >> You may try: >> - increase concurrentçcompaction to 8 (max in 2.1.x) >> - increase compaction_throupghput to more than 16MB/s (48 may be a good >> start) >> >> >> What kind of data are you storing in theses tables ? timeseries ? >> >> >> >> 2016-03-21 23:37 GMT+01:00 Gianluca Borello <gianl...@sysdig.com>: >> > Thank you for your reply, definitely appreciate the tip on the >> compressed >> > size. >> > >> > I understand your point, in fact whenever we bootstrap a new node we >> see a >> > huge number of pending compactions (in the order of thousands), and they >> > usually decrease steadily until they reach 0 in just a few hours. With >> this >> > node, however, we are way beyond that point, it has been 3 days since >> the >> > number of pending compaction started fluctuating around ~150 without any >> > sign of going down (I can see from Opscenter it's almost a straight line >> > starting a few hours after the bootstrap). In particular, to reply to >> your >> > point: >> > >> > - The number of sstables for this CF on this node is around 250, which >> is in >> > the same range of all the other nodes in the cluster (I counted the >> number >> > on each one of them, and every node is in the 200-400 range) >> > >> > - This theory doesn't seem to explain why, when doing "nodetool drain", >> the >> > compactions completely stop after a few minutes and I get something >> such as: >> > >> > $ nodetool compactionstats >> > pending tasks: 128 >> > >> > So no compactions being executed (since there is no more write >> activity), >> > but the pending number is still high. >> > >> > Thanks again >> > >> > >> > On Mon, Mar 21, 2016 at 3:19 PM, Jeff Jirsa <jeff.ji...@crowdstrike.com >> > >> > wrote: >> >> >> >> > We added a bunch of new nodes to a cluster (2.1.13) and everything >> went >> >> > fine, except for the number of pending compactions that is staying >> quite >> >> > high on a subset of the new nodes. Over the past 3 days, the pending >> >> > compactions have never been less than ~130 on such nodes, with peaks >> of >> >> > ~200. >> >> >> >> When you bootstrap with Vnodes, you end up with thousands (or tens of >> >> thousands) of sstables – with 256 Vnodes (default) * 20 sstables per >> node, >> >> your resulting node will have 5k sstables. It takes quite a while for >> >> compaction to chew through that. If you added a bunch of nodes in >> sequence, >> >> you’d have 5k on the first node, then potentailly 10k on the next, and >> could >> >> potentially keep increasing as you start streaming from nodes that >> have way >> >> too many sstables. This is one of the reasons that many people who >> have to >> >> grow their clusters frequently try not to use vnodes. >> >> >> >> From your other email: >> >> >> >> > Also related to this point, now I'm seeing something even more odd: >> some >> >> > compactions are way bigger than the size of the column family >> itself, such >> >> > as: >> >> >> >> The size reported by compactionstats is the uncompressed size – if >> you’re >> >> using compression, it’s perfectly reasonable for 30G of data to show >> up as >> >> 118G of data during compaction. >> >> >> >> - Jeff >> >> >> >> From: Gianluca Borello >> >> Reply-To: "user@cassandra.apache.org" >> >> Date: Monday, March 21, 2016 at 12:50 PM >> >> To: "user@cassandra.apache.org" >> >> Subject: Pending compactions not going down on some nodes of the >> cluster >> >> >> >> Hi, >> >> >> >> We added a bunch of new nodes to a cluster (2.1.13) and everything went >> >> fine, except for the number of pending compactions that is staying >> quite >> >> high on a subset of the new nodes. Over the past 3 days, the pending >> >> compactions have never been less than ~130 on such nodes, with peaks of >> >> ~200. On the other nodes, they correctly fluctuate between 0 and ~20, >> which >> >> has been our norm for a long time. >> >> >> >> We are quite paranoid about pending compactions because in the past >> such >> >> high number caused a lot of data being brought in memory during some >> reads >> >> and that triggered a chain reaction of full GCs that brought down our >> >> cluster, so we try to monitor them closely. >> >> >> >> Some data points that should let the situation speak for itself: >> >> >> >> - We use LCS for all our column families >> >> >> >> - The cluster is operating absolutely fine and seems healthy, and every >> >> node is handling pretty much the same load in terms of reads and >> writes. >> >> Also, these nodes with higher pending compactions don't seem in any way >> >> performing worse than the others >> >> >> >> - The pending compactions don't go down even when setting the >> compaction >> >> throughput to unlimited for a very long time >> >> >> >> - This is the typical output of compactionstats and tpstats: >> >> >> >> $ nodetool compactionstats >> >> pending tasks: 137 >> >> compaction type keyspace table completed >> total >> >> unit progress >> >> Compaction draios message_data60 6111208394 >> 6939536890 >> >> bytes 88.06% >> >> Compaction draios message_data1 26473390790 >> 37243294809 >> >> bytes 71.08% >> >> Active compaction remaining time : n/a >> >> >> >> $ nodetool tpstats >> >> Pool Name Active Pending Completed Blocked >> >> All time blocked >> >> CounterMutationStage 0 0 0 0 >> >> 0 >> >> ReadStage 1 0 111766844 0 >> >> 0 >> >> RequestResponseStage 0 0 244259493 0 >> >> 0 >> >> MutationStage 0 0 163268653 0 >> >> 0 >> >> ReadRepairStage 0 0 8933323 0 >> >> 0 >> >> GossipStage 0 0 363003 0 >> >> 0 >> >> CacheCleanupExecutor 0 0 0 0 >> >> 0 >> >> AntiEntropyStage 0 0 0 0 >> >> 0 >> >> MigrationStage 0 0 2 0 >> >> 0 >> >> Sampler 0 0 0 0 >> >> 0 >> >> ValidationExecutor 0 0 0 0 >> >> 0 >> >> CommitLogArchiver 0 0 0 0 >> >> 0 >> >> MiscStage 0 0 0 0 >> >> 0 >> >> MemtableFlushWriter 0 0 32644 0 >> >> 0 >> >> MemtableReclaimMemory 0 0 32644 0 >> >> 0 >> >> PendingRangeCalculator 0 0 527 0 >> >> 0 >> >> MemtablePostFlush 0 0 36565 0 >> >> 0 >> >> CompactionExecutor 2 70 108621 0 >> >> 0 >> >> InternalResponseStage 0 0 0 0 >> >> 0 >> >> HintedHandoff 0 0 10 0 >> >> 0 >> >> Native-Transport-Requests 6 0 188996929 0 >> >> 79122 >> >> >> >> Message type Dropped >> >> RANGE_SLICE 0 >> >> READ_REPAIR 0 >> >> PAGED_RANGE 0 >> >> BINARY 0 >> >> READ 0 >> >> MUTATION 0 >> >> _TRACE 0 >> >> REQUEST_RESPONSE 0 >> >> COUNTER_MUTATION 0 >> >> >> >> - If I do a nodetool drain on such nodes, and then wait for a while, >> the >> >> number of pending compactions stays high even if there are no >> compactions >> >> being executed anymore and the node is completely idle: >> >> >> >> $ nodetool compactionstats >> >> pending tasks: 128 >> >> >> >> - It's also interesting to notice how the compaction in the previous >> >> example is trying to compact ~37 GB, which is essentially the whole >> size of >> >> the column family message_data1 as reported by cfstats: >> >> >> >> $ nodetool cfstats -H draios.message_data1 >> >> Keyspace: draios >> >> Read Count: 208168 >> >> Read Latency: 2.4791508685292647 ms. >> >> Write Count: 502529 >> >> Write Latency: 0.20701542000561163 ms. >> >> Pending Flushes: 0 >> >> Table: message_data1 >> >> SSTable count: 261 >> >> SSTables in each level: [43/4, 92/10, 125/100, 0, 0, 0, 0, 0, 0] >> >> Space used (live): 36.98 GB >> >> Space used (total): 36.98 GB >> >> Space used by snapshots (total): 0 bytes >> >> Off heap memory used (total): 36.21 MB >> >> SSTable Compression Ratio: 0.15461126176169512 >> >> Number of keys (estimate): 101025 >> >> Memtable cell count: 229344 >> >> Memtable data size: 82.4 MB >> >> Memtable off heap memory used: 0 bytes >> >> Memtable switch count: 83 >> >> Local read count: 208225 >> >> Local read latency: 2.479 ms >> >> Local write count: 502581 >> >> Local write latency: 0.208 ms >> >> Pending flushes: 0 >> >> Bloom filter false positives: 11497 >> >> Bloom filter false ratio: 0.04307 >> >> Bloom filter space used: 94.97 KB >> >> Bloom filter off heap memory used: 92.93 KB >> >> Index summary off heap memory used: 57.88 KB >> >> Compression metadata off heap memory used: 36.06 MB >> >> Compacted partition minimum bytes: 447 bytes >> >> Compacted partition maximum bytes: 34.48 MB >> >> Compacted partition mean bytes: 1.51 MB >> >> Average live cells per slice (last five minutes): 26.269698643294515 >> >> Maximum live cells per slice (last five minutes): 100.0 >> >> Average tombstones per slice (last five minutes): 0.0 >> >> Maximum tombstones per slice (last five minutes): 0.0 >> >> >> >> - There are no warnings or errors in the log, even after a clean >> restart >> >> >> >> - Restarting the node doesn't seem to have any effect on the number of >> >> pending compactions >> >> >> >> Any help would be very appreciated. >> >> >> >> Thank you for reading >> >> >> > >> >> >> >> -- >> Close the World, Open the Net >> http://www.linux-wizard.net >> > >
