Thanks Jeff. I'm trying to figure out why the tombstones scans are happening if possible eliminate it.
On Sat, Feb 23, 2019, 10:50 PM Jeff Jirsa <jji...@gmail.com> wrote: > G1GC with an 8g heap may be slower than CMS. Also you don’t typically set > new gen size on G1. > > Again though - what problem are you solving here? If you’re serving reads > and sitting under 50% cpu, it’s not clear to me what you’re trying to fix. > Tombstones scanned won’t matter for your table, so if that’s your only > concern, I’d ignore it. > > > > -- > Jeff Jirsa > > > On Feb 23, 2019, at 7:26 PM, Rahul Reddy <rahulreddy1...@gmail.com> wrote: > > ```jvm setting > > -XX:+UseThreadPriorities > -XX:ThreadPriorityPolicy=42 > -XX:+HeapDumpOnOutOfMemoryError > -Xss256k > -XX:StringTableSize=1000003 > -XX:+AlwaysPreTouch > -XX:-UseBiasedLocking > -XX:+UseTLAB > -XX:+ResizeTLAB > -XX:+UseNUMA > -XX:+PerfDisableSharedMem > -Djava.net.preferIPv4Stack=true > -XX:+UseG1GC > -XX:G1RSetUpdatingPauseTimePercent=5 > -XX:MaxGCPauseMillis=500 > -XX:+PrintGCDetails > -XX:+PrintGCDateStamps > -XX:+PrintHeapAtGC > -XX:+PrintTenuringDistribution > -XX:+PrintGCApplicationStoppedTime > -XX:+PrintPromotionFailure > -XX:+UseGCLogFileRotation > -XX:NumberOfGCLogFiles=10 > -XX:GCLogFileSize=10M > > Total memory > free > total used free shared buffers cached > Mem: 16434004 16125340 308664 60 172872 5565184 > -/+ buffers/cache: 10387284 6046720 > Swap: 0 0 0 > > Heap settings in cassandra-env.sh > MAX_HEAP_SIZE="8192M" > HEAP_NEWSIZE="800M" > ``` > > On Sat, Feb 23, 2019, 10:15 PM Rahul Reddy <rahulreddy1...@gmail.com> > wrote: > >> Thanks Jeff, >> >> Since low writes and high reads most of the time data in memtables only. >> When I noticed intially issue no stables on disk everything in memtable >> only. >> >> On Sat, Feb 23, 2019, 10:01 PM Jeff Jirsa <jji...@gmail.com> wrote: >> >>> Also given your short ttl and low write rate, you may want to think >>> about how you can keep more in memory - this may mean larger memtable and >>> high flush thresholds (reading from the memtable), or perhaps the partition >>> cache (if you are likely to read the same key multiple times). You’ll also >>> probably win some with basic perf and GC tuning, but can’t really do that >>> via email. Cassandra-8150 has some pointers. >>> >>> -- >>> Jeff Jirsa >>> >>> >>> On Feb 23, 2019, at 6:52 PM, Jeff Jirsa <jji...@gmail.com> wrote: >>> >>> You’ll only ever have one tombstone per read, so your load is based on >>> normal read rate not tombstones. The metric isn’t wrong, but it’s not >>> indicative of a problem here given your data model. >>> >>> You’re using STCS do you may be reading from more than one sstable if >>> you update column2 for a given column1, otherwise you’re probably just >>> seeing normal read load. Consider dropping your compression chunk size a >>> bit (given the sizes in your cfstats I’d probably go to 4K instead of 64k), >>> and maybe consider LCS or TWCS instead of STCS (Which is appropriate >>> depends on a lot of factors, but STCS is probably causing a fair bit of >>> unnecessary compactions and probably is very slow to expire data). >>> >>> -- >>> Jeff Jirsa >>> >>> >>> On Feb 23, 2019, at 6:31 PM, Rahul Reddy <rahulreddy1...@gmail.com> >>> wrote: >>> >>> Do you see anything wrong with this metric. >>> >>> metric to scan tombstones >>> >>> increase(cassandra_Table_TombstoneScannedHistogram{keyspace="mykeyspace",Table="tablename",function="Count"}[5m]) >>> >>> And sametime CPU Spike to 50% whenever I see high tombstone alert. >>> >>> On Sat, Feb 23, 2019, 9:25 PM Jeff Jirsa <jji...@gmail.com> wrote: >>> >>>> Your schema is such that you’ll never read more than one tombstone per >>>> select (unless you’re also doing range reads / table scans that you didn’t >>>> mention) - I’m not quite sure what you’re alerting on, but you’re not going >>>> to have tombstone problems with that table / that select. >>>> >>>> -- >>>> Jeff Jirsa >>>> >>>> >>>> On Feb 23, 2019, at 5:55 PM, Rahul Reddy <rahulreddy1...@gmail.com> >>>> wrote: >>>> >>>> Changing gcgs didn't help >>>> >>>> CREATE KEYSPACE ksname WITH replication = {'class': >>>> 'NetworkTopologyStrategy', 'dc1': '3', 'dc2': '3'} AND durable_writes = >>>> true; >>>> >>>> >>>> ```CREATE TABLE keyspace."table" ( >>>> "column1" text PRIMARY KEY, >>>> "column2" text >>>> ) WITH bloom_filter_fp_chance = 0.01 >>>> AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'} >>>> AND comment = '' >>>> AND compaction = {'class': >>>> 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy', >>>> 'max_threshold': '32', 'min_threshold': '4'} >>>> AND compression = {'chunk_length_in_kb': '64', 'class': >>>> 'org.apache.cassandra.io.compress.LZ4Compressor'} >>>> AND crc_check_chance = 1.0 >>>> AND dclocal_read_repair_chance = 0.1 >>>> AND default_time_to_live = 18000 >>>> AND gc_grace_seconds = 60 >>>> 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 = '99PERCENTILE'; >>>> >>>> flushed table and took tsstabledump >>>> grep -i '"expired" : true' SSTables.txt|wc -l >>>> 16439 >>>> grep -i '"expired" : false' SSTables.txt |wc -l >>>> 2657 >>>> >>>> ttl is 4 hours. >>>> >>>> INSERT INTO keyspace."TABLE_NAME" ("column1", "column2") VALUES (?, ?) >>>> USING TTL(4hours) ?'; >>>> SELECT * FROM keyspace."TABLE_NAME" WHERE "column1" = ?'; >>>> >>>> metric to scan tombstones >>>> >>>> increase(cassandra_Table_TombstoneScannedHistogram{keyspace="mykeyspace",Table="tablename",function="Count"}[5m]) >>>> >>>> during peak hours. we only have couple of hundred inserts and 5-8k >>>> reads/s per node. >>>> ``` >>>> >>>> ```tablestats >>>> Read Count: 605231874 >>>> Read Latency: 0.021268529760215503 ms. >>>> Write Count: 2763352 >>>> Write Latency: 0.027924007871599422 ms. >>>> Pending Flushes: 0 >>>> Table: name >>>> SSTable count: 1 >>>> Space used (live): 1413203 >>>> Space used (total): 1413203 >>>> Space used by snapshots (total): 0 >>>> Off heap memory used (total): 28813 >>>> SSTable Compression Ratio: 0.5015090954531143 >>>> Number of partitions (estimate): 19568 >>>> Memtable cell count: 573 >>>> Memtable data size: 22971 >>>> Memtable off heap memory used: 0 >>>> Memtable switch count: 6 >>>> Local read count: 529868919 >>>> Local read latency: 0.020 ms >>>> Local write count: 2707371 >>>> Local write latency: 0.024 ms >>>> Pending flushes: 0 >>>> Percent repaired: 0.0 >>>> Bloom filter false positives: 1 >>>> Bloom filter false ratio: 0.00000 >>>> Bloom filter space used: 23888 >>>> Bloom filter off heap memory used: 23880 >>>> Index summary off heap memory used: 4717 >>>> Compression metadata off heap memory used: 216 >>>> Compacted partition minimum bytes: 73 >>>> Compacted partition maximum bytes: 124 >>>> Compacted partition mean bytes: 99 >>>> Average live cells per slice (last five minutes): 1.0 >>>> Maximum live cells per slice (last five minutes): 1 >>>> Average tombstones per slice (last five minutes): 1.0 >>>> Maximum tombstones per slice (last five minutes): 1 >>>> Dropped Mutations: 0 >>>> histograms >>>> Percentile SSTables Write Latency Read Latency Partition >>>> Size Cell Count >>>> (micros) (micros) >>>> (bytes) >>>> 50% 0.00 20.50 17.08 >>>> 86 1 >>>> 75% 0.00 24.60 20.50 >>>> 124 1 >>>> 95% 0.00 35.43 29.52 >>>> 124 1 >>>> 98% 0.00 35.43 42.51 >>>> 124 1 >>>> 99% 0.00 42.51 51.01 >>>> 124 1 >>>> Min 0.00 8.24 5.72 >>>> 73 0 >>>> Max 1.00 42.51 152.32 >>>> 124 1 >>>> ``` >>>> >>>> 3 node in dc1 and 3 node in dc2 cluster. With instanc type aws ec2 >>>> m4.xlarge >>>> >>>> On Sat, Feb 23, 2019, 7:47 PM Jeff Jirsa <jji...@gmail.com> wrote: >>>> >>>>> Would also be good to see your schema (anonymized if needed) and the >>>>> select queries you’re running >>>>> >>>>> >>>>> -- >>>>> Jeff Jirsa >>>>> >>>>> >>>>> On Feb 23, 2019, at 4:37 PM, Rahul Reddy <rahulreddy1...@gmail.com> >>>>> wrote: >>>>> >>>>> Thanks Jeff, >>>>> >>>>> I'm having gcgs set to 10 mins and changed the table ttl also to 5 >>>>> hours compared to insert ttl to 4 hours . Tracing on doesn't show any >>>>> tombstone scans for the reads. And also log doesn't show tombstone scan >>>>> alerts. Has the reads are happening 5-8k reads per node during the peak >>>>> hours it shows 1M tombstone scans count per read. >>>>> >>>>> On Fri, Feb 22, 2019, 11:46 AM Jeff Jirsa <jji...@gmail.com> wrote: >>>>> >>>>>> If all of your data is TTL’d and you never explicitly delete a cell >>>>>> without using s TTL, you can probably drop your GCGS to 1 hour (or less). >>>>>> >>>>>> Which compaction strategy are you using? You need a way to clear out >>>>>> those tombstones. There exist tombstone compaction sub properties that >>>>>> can >>>>>> help encourage compaction to grab sstables just because they’re full of >>>>>> tombstones which will probably help you. >>>>>> >>>>>> >>>>>> -- >>>>>> Jeff Jirsa >>>>>> >>>>>> >>>>>> On Feb 22, 2019, at 8:37 AM, Kenneth Brotman < >>>>>> kenbrot...@yahoo.com.invalid> wrote: >>>>>> >>>>>> Can we see the histogram? Why wouldn’t you at times have that many >>>>>> tombstones? Makes sense. >>>>>> >>>>>> >>>>>> >>>>>> Kenneth Brotman >>>>>> >>>>>> >>>>>> >>>>>> *From:* Rahul Reddy [mailto:rahulreddy1...@gmail.com >>>>>> <rahulreddy1...@gmail.com>] >>>>>> *Sent:* Thursday, February 21, 2019 7:06 AM >>>>>> *To:* user@cassandra.apache.org >>>>>> *Subject:* Tombstones in memtable >>>>>> >>>>>> >>>>>> >>>>>> We have small table records are about 5k . >>>>>> >>>>>> All the inserts comes as 4hr ttl and we have table level ttl 1 day >>>>>> and gc grace seconds has 3 hours. We do 5k reads a second during peak >>>>>> load >>>>>> During the peak load seeing Alerts for tomstone scanned histogram >>>>>> reaching >>>>>> million. >>>>>> >>>>>> Cassandra version 3.11.1. Please let me know how can this tombstone >>>>>> scan can be avoided in memtable >>>>>> >>>>>>