Re: Tombstones in memtable
Reads increase on all most all nodes same is the case with CPU. it's goes
high on all nodes
On Sat, Feb 23, 2019, 11:04 PM Kenneth Brotman
wrote:
> When the CPU utilization spikes from 5-10% to 50%, how many nodes does it
> happen to at the same time?
>
>
>
> *From:* Rahul Reddy [mailto:rahulreddy1...@gmail.com]
> *Sent:* Saturday, February 23, 2019 7:26 PM
> *To:* user@cassandra.apache.org
> *Subject:* Re: Tombstones in memtable
>
>
>
> ```jvm setting
>
>
>
> -XX:+UseThreadPriorities
>
> -XX:ThreadPriorityPolicy=42
>
> -XX:+HeapDumpOnOutOfMemoryError
>
> -Xss256k
>
> -XX:StringTableSize=103
>
> -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 sharedbuffers cached
>
> Mem: 16434004 16125340 308664 60 1728725565184
>
> -/+ buffers/cache: 103872846046720
>
> 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
> 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 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 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 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 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 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.t
RE: Tombstones in memtable
When the CPU utilization spikes from 5-10% to 50%, how many nodes does it
happen to at the same time?
From: Rahul Reddy [mailto:rahulreddy1...@gmail.com]
Sent: Saturday, February 23, 2019 7:26 PM
To: user@cassandra.apache.org
Subject: Re: Tombstones in memtable
```jvm setting
-XX:+UseThreadPriorities
-XX:ThreadPriorityPolicy=42
-XX:+HeapDumpOnOutOfMemoryError
-Xss256k
-XX:StringTableSize=103
-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 sharedbuffers cached
Mem: 16434004 16125340 308664 60 1728725565184
-/+ buffers/cache: 103872846046720
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 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 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 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 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 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 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.
```
```table
Re: Tombstones in memtable
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 wrote:
>
> ```jvm setting
>
> -XX:+UseThreadPriorities
> -XX:ThreadPriorityPolicy=42
> -XX:+HeapDumpOnOutOfMemoryError
> -Xss256k
> -XX:StringTableSize=103
> -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 sharedbuffers cached
> Mem: 16434004 16125340 308664 60 1728725565184
> -/+ buffers/cache: 103872846046720
> 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 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 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 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 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 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
>>> 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_
Re: Tombstones in memtable
```jvm setting
-XX:+UseThreadPriorities
-XX:ThreadPriorityPolicy=42
-XX:+HeapDumpOnOutOfMemoryError
-Xss256k
-XX:StringTableSize=103
-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 sharedbuffers cached
Mem: 16434004 16125340 308664 60 1728725565184
-/+ buffers/cache: 103872846046720
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 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 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 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
>> 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 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
>>> 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.
Re: Tombstones in memtable
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 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 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 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 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
>> 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: 0.0
>> 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 c
Re: Tombstones in memtable
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 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 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 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 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: 0.0
Bloom filter space used: 23888
Bloom filter off heap memory used: 23880
Index summary off heap memory u
Re: Tombstones in memtable
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 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 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 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: 0.0
>>> 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
RE: Tombstones in memtable
Rahul,
You wrote that during peak hours you only have a couple hundred inserts per
node so now I’m not sure why the default settings wouldn’t have worked just
fine. I sense there is more to the story. What else could explain those
tombstones?
From: Rahul Reddy [mailto:rahulreddy1...@gmail.com]
Sent: Saturday, February 23, 2019 5:56 PM
To: user@cassandra.apache.org
Subject: Re: Tombstones in memtable
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: 0.0
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 LatencyPartition Size
Cell Count
(micros) (micros) (bytes)
50% 000 20.50 17.0886
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 5.7273
0
Max 1.00 42.51152.32 124
1
```
3 node in
Re: Tombstones in memtable
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 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 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: 0.0
> 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 LatencyPartition
> SizeCell 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 42.51152.32
> 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 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
>> 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
Re: Tombstones in memtable
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 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: 0.0
> 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 LatencyPartition Size
> Cell Count
> (micros) (micros) (bytes)
>
> 50% 0.00 20.50 17.0886
> 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 5.7273
> 0
> Max 1.00 42.51152.32 124
> 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 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 wrote:
>
RE: Tombstones in memtable
Rahul, Please see this DataStax article which suggests you might be using Cassandra as a queue-like dataset – and that’s an anti-pattern for Cassandra. It could be you need to use a different database. It could be your data model is wrong: https://www.datastax.com/dev/blog/cassandra-anti-patterns-queues-and-queue-like-datasets Kenneth Brotman From: Jeff Jirsa [mailto:jji...@gmail.com] Sent: Saturday, February 23, 2019 4:47 PM To: user@cassandra.apache.org Subject: Re: Tombstones in memtable 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 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 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 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
Re: Tombstones in memtable
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: 0.0
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 LatencyPartition Size
Cell Count
(micros) (micros) (bytes)
50% 0.00 20.50 17.0886
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 5.7273
0
Max 1.00 42.51152.32 124
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 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 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 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.
Re: Tombstones in memtable
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 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 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 >>> 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
Re: Tombstones in memtable
I’m not parsing this - did the lower gcgs help or not ? Seeing the table histograms is the next step if this is still a problem The table level TTL doesn’t matter if you set a TTL on each insert -- Jeff Jirsa > On Feb 23, 2019, at 4:37 PM, Rahul Reddy 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 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 >>> 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
Re: Tombstones in memtable
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 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 > 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 > >
Re: tombstones threshold warning
Thanks Ken, further investigating what I found is the tombstones which I am
seeing are from null values in the collection objects. Tombstones are also
inserted into when initial collection values are inserted but seems like
they are not counted towards threshold warning and do not show up in
tracing. These tests I did on 3.11.3 version of cassandra.
Record inserted with values in collection objects - I see tombstones but
they do not show up in tracing.
"partition" : {
"key" : [ "e7cd5752-bc0d-4157-a80f-7523add8dbcd" ],
"position" : 121
},
"rows" : [
{
"type" : "row",
"position" : 528,
"clustering" : [ "ELVIS" ],
"liveness_info" : { "tstamp" : "2019-02-21T21:34:06.574848Z" },
"cells" : [
{ "name" : "frozen_race", "value" : {"race_title": "Ronde van
Gelderland", "race_date": "2015-04-19 00:00:00.000Z", "race_time":
"03:22:23"} },
{ "name" : "basics_udt", "deletion_info" : { "marked_deleted" :
"2019-02-21T21:34:06.574847Z", "local_delete_time" : "2019-02-21T21:34:06Z"
} },
{ "name" : "basics_udt", "path" : [ "birthday" ], "value" :
"1993-06-18 00:00:00.000Z" },
{ "name" : "basics_udt", "path" : [ "nationality" ], "value" :
"New Zealand" },
{ "name" : "events_list", "deletion_info" : { "marked_deleted" :
"2019-02-21T21:34:06.574847Z", "local_delete_time" : "2019-02-21T21:34:06Z"
} },
{ "name" : "events_list", "path" : [
"6ab41176-3620-11e9-81ac-87caa6eca935" ], "value" : "list-element1" },
{ "name" : "events_list", "path" : [
"6ab41177-3620-11e9-81ac-87caa6eca935" ], "value" : "list-element2" },
{ "name" : "frozen_race_list", "deletion_info" : {
"marked_deleted" : "2019-02-21T21:34:06.574847Z", "local_delete_time" :
"2019-02-21T21:34:06Z" } },
{ "name" : "frozen_race_list", "path" : [
"6ab41178-3620-11e9-81ac-87caa6eca935" ], "value" : {"race_title":
"Rabobank 7-Dorpenomloop Aalburg", "race_date": "2015-05-09 00:00:00.000Z",
"race_time": "02:58:33"} },
{ "name" : "frozen_race_list", "path" : [
"6ab41179-3620-11e9-81ac-87caa6eca935" ], "value" : {"race_title": "Ronde
van Gelderland", "race_date": "2015-04-19 00:00:00.000Z", "race_time":
"03:22:23"} },
{ "name" : "teams_map", "deletion_info" : { "marked_deleted" :
"2019-02-21T21:34:06.574847Z", "local_delete_time" : "2019-02-21T21:34:06Z"
} },
{ "name" : "teams_map", "path" : [ "1" ], "value" : "map-value1"
},
{ "name" : "teams_map", "path" : [ "2" ], "value" : "map-value2"
},
{ "name" : "teams_set", "deletion_info" : { "marked_deleted" :
"2019-02-21T21:34:06.574847Z", "local_delete_time" : "2019-02-21T21:34:06Z"
} },
{ "name" : "teams_set", "path" : [ "set-element1" ], "value" : ""
},
{ "name" : "teams_set", "path" : [ "set-element2" ], "value" : ""
}
cassandra@cqlsh:dev_ticket> select * from collsndudt where id =
e7cd5752-bc0d-4157-a80f-7523add8dbcd and lastname = 'ELVIS';
id | lastname |
basics_udt
| events_list|
frozen_race
|
frozen_race_list
| teams_map | teams_set
--+--+---++---+---++--
e7cd5752-bc0d-4157-a80f-7523add8dbcd |ELVIS | {birthday: '1993-06-18
00:00:00.00+', nationality: 'New Zealand', height: null, weight:
null} | ['list-element1', 'list-element2'] | {race_title: 'Ronde van
Gelderland', race_date: '2015-04-19 00:00:00.00+', race_time:
'03:22:23'} | [{race_title: 'Rabobank 7-Dorpenomloop Aalburg', race_date:
'2015-05-09 00:00:00.00+', race_time: '02:58:33'}, {race_title:
'Ronde van Gelderland', race_date: '2015-04-19 00:00:00.00+',
race_time: '03:22:23'}] | {1: 'map-value1', 2: 'map-value2'} |
{'set-element1', 'set-element2'}
(1 rows)
Tracing session: aa82f2c0-3621-11e9-81ac-87caa6eca935
activity
|
timestamp | source| source_elapsed | client
-++---++---
Execute CQL3 query | 2019-02-21 21:43:03.404000 | 10.216.87.180
| 0 | 127.0.0.1
Parsing select * from collsndudt where id =
e7cd5752-bc0d-4157-a80f-7523add8dbcd and lastname = 'ELVIS'; [CoreTh
