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]
>>>>> 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
