Cassandra webinars August 2013

CASSANDRA COMMUNITY WEBINARS AUGUST 2013
IN CASE OF EMERGENCY,
BREAK GLASS
Aaron Morton
@aaronmorton
Co-Founder & Principal Consultant
www.thelastpickle.com
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

AboutThe Last Pickle
Work with clients to deliver and improve
Apache Cassandra based solutions.
Apache Cassandra Committer, DataStax MVP,
Hector Maintainer, 6+ years combined
Cassandra experience.
Based in New Zealand & Austin,TX.

Platform
Tools
Problems
Maintenance

The Platform

The Platform & Clients

The Platform & Running Clients

The Platform & Reality
Consistency
Availability
Partition Tolerance

The Platform & Consistency
Strong Consistency
(R + W > N)
Eventual Consistency
(R + W <= N)www.thelastpickle.com

What Price Consistency?
In a Multi DC cluster QUOURM
and EACH_QUOURM involve
cross DC latency.

The Platform & Availability
Maintain Consistency Level UP
nodes for each Token Range.

Best Case Failure with N=9 and RF 3, 100% Availability
Replica 1
Replica 2
Replica 3
Range A

Worst Case Failure with N=9 and RF 3, 78% Availability
Range B
Range A

The Platform & PartitionTolerance
A failed node does not create
a partition.

Partitions occur when the
network fails.

The Storage Engine
Optimised for
Writes.

Write Path
Append to Write Ahead Log.
(fsync every 10s by default, other options available)

Write Path
Merge new Columns into
Memtable.
(Lock free, always in memory.)

Write Path... Later
Asynchronously ﬂush
Memtable to a new SSTable on
disk.
(May be 10’s or 100’s of MB in size.)

SSTable Files
*-Data.db
*-Index.db
*-Filter.db
(And others)

Row Fragmentation
SSTable 1
foo:
dishwasher (ts 10):
tomato
purple (ts 10):
cromulent
SSTable 2
foo:
frink (ts 20):
ﬂayven
monkey (ts 10):
embiggins
SSTable 3 SSTable 4
foo:
dishwasher (ts 15):
tomacco
SSTable 5

Read Path
Read columns from each
SSTable, then merge results.
(Roughly speaking.)

Read Path
Use Bloom Filter to
determine if a row key does
not exist in a SSTable.
(In memory)

Read Path
Search for prior key in
*-Index.db sample.
(In memory)

Read Path
Scan *-Index.db from
prior key to ﬁnd the search
key and its’ *-Data.db
offset.
(On disk.)

Read Path
Read *-Data.db from
offset, all columns or speciﬁc
pages.

Read purple, monkey, dishwasher
SSTable 1-Data.db
foo:
dishwasher (ts 10):
tomato
purple (ts 10):
cromulent
SSTable 2-Data.db
foo:
frink (ts 20):
ﬂayven
monkey (ts 10):
embiggins
SSTable 3-Data.db SSTable 4-Data.db
foo:
dishwasher (ts 15):
tomacco
SSTable 5-Data.db
Bloom Filter
Index Sample
SSTable 1-Index.db
Bloom Filter
Index Sample
SSTable 2-Index.db
Bloom Filter
Index Sample
SSTable 3-Index.db
Bloom Filter
Index Sample
SSTable 4-Index.db
Bloom Filter
Index Sample
SSTable 5-Index.db
Memory
Disk

Read With Key Cache
SSTable 1-Data.db
foo:
dishwasher (ts 10):
tomato
purple (ts 10):
cromulent
SSTable 2-Data.db
foo:
frink (ts 20):
ﬂayven
monkey (ts 10):
embiggins
foo:
dishwasher (ts 15):
tomacco
SSTable 5-Data.db
Key Cache
Index Sample
SSTable 1-Index.db
Key Cache
Index Sample
SSTable 2-Index.db
Key Cache
Index Sample
SSTable 3-Index.db
Key Cache
Index Sample
SSTable 4-Index.db
Key Cache
Index Sample
SSTable 5-Index.db
Memory
Disk
Bloom Filter Bloom Filter Bloom Filter Bloom Filter Bloom Filter

Read with Row Cache
Row Cache
SSTable 1-Data.db
foo:
dishwasher (ts 10):
tomato
purple (ts 10):
cromulent
SSTable 2-Data.db
foo:
frink (ts 20):
ﬂayven
monkey (ts 10):
embiggins
foo:
dishwasher (ts 15):
tomacco
SSTable 5-Data.db
Key Cache
Index Sample
SSTable 1-Index.db
Key Cache
Index Sample
SSTable 2-Index.db
Key Cache
Index Sample
SSTable 3-Index.db
Key Cache
Index Sample
SSTable 4-Index.db
Key Cache
Index Sample
SSTable 5-Index.db
Memory
Disk
Bloom Filter Bloom Filter Bloom Filter Bloom Filter Bloom Filter

Performant Reads
Design queries to read from a
small number of SSTables.

Performant Reads
Read a small number of
named columns or a slice of
columns.

Performant Reads
Design data model to support
current application
requirements.

Logging
Conﬁgure via
log4j-server.properties
and
StorageServiceMBean

DEBUG Logging For One Class
log4j.logger.org.apache.cassandra.thrift.
CassandraServer=DEBUG

Reading Logs
INFO [OptionalTasks:1] 2013-04-20 14:03:50,787
MeteredFlusher.java (line 62) flushing high-traffic column
family CFS(Keyspace='KS1', ColumnFamily='CF1') (estimated
403858136 bytes)
INFO [OptionalTasks:1] 2013-04-20 14:03:50,787
ColumnFamilyStore.java (line 634) Enqueuing flush of Memtable-
CF1@1333396270(145839277/403858136 serialized/live bytes,
1742365 ops)
INFO [FlushWriter:42] 2013-04-20 14:03:50,788 Memtable.java
(line 266) Writing Memtable-CF1@1333396270(145839277/403858136
serialized/live bytes, 1742365 ops)

GC Logs
cassandra-env.sh
# GC logging options -- uncomment to enable
# JVM_OPTS="$JVM_OPTS -XX:+PrintGCDetails"
# JVM_OPTS="$JVM_OPTS -XX:+PrintGCDateStamps"
# JVM_OPTS="$JVM_OPTS -XX:+PrintHeapAtGC"
# JVM_OPTS="$JVM_OPTS -XX:+PrintTenuringDistribution"
# JVM_OPTS="$JVM_OPTS -XX:+PrintGCApplicationStoppedTime"
# JVM_OPTS="$JVM_OPTS -XX:+PrintPromotionFailure"
# JVM_OPTS="$JVM_OPTS -XX:PrintFLSStatistics=1"
# JVM_OPTS="$JVM_OPTS -Xloggc:/var/log/cassandra/gc-`date +
%s`.log"

ParNew GC Starting
{Heap before GC invocations=224115 (full 111):
par new generation total 873856K, used 717289K ...)
eden space 699136K, 100% used ...)
from space 174720K, 10% used ...)
to space 174720K, 0% used ...)

Tenuring Distribution
240217.053: [ParNew
Desired survivor size 89456640 bytes, new threshold 4 (max 4)
- age 1: 22575936 bytes, 22575936 total
- age 2: 350616 bytes, 22926552 total
- age 3: 4380888 bytes, 27307440 total
- age 4: 1155104 bytes, 28462544 total

ParNew GC Finishing
Heap after GC invocations=224116 (full 111):

nodetool info
Token : 0
Gossip active : true
Load : 130.64 GB
Generation No : 1369334297
Uptime (seconds) : 29438
Heap Memory (MB) : 3744.27 / 8025.38
Data Center : east
Rack : rack1
Exceptions : 0
Key Cache : size 104857584 (bytes), capacity 104857584
(bytes), 25364985 hits, 34874180 requests, 0.734 recent hit
rate, 14400 save period in seconds
Row Cache : size 0 (bytes), capacity 0...

nodetool ring
Note: Ownership information does not include topology, please specify a keyspace.
Address DC Rack Status State Load Owns Token
10.1.64.11 east rack1 Up Normal 130.64 GB 12.50% 0
10.1.65.8 west rack1 Up Normal 88.79 GB 0.00% 1
10.1.64.78 east rack1 Up Normal 52.66 GB 12.50% 212...216
10.1.65.181 west rack1 Up Normal 65.99 GB 0.00% 212...217

nodetool ring KS1
Address DC Rack Status State Load Effective-Ownership Token
10.1.64.11 east rack1 Up Normal 130.72 GB 12.50% 0
10.1.65.8 west rack1 Up Normal 88.81 GB 12.50% 1

nodetool status
$ nodetool status
Datacenter: ams01 (Replication Factor 3)
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns Host ID Rack
UN 10.70.48.23 38.38 GB 256 19.0% 7c5fdfad-63c6-4f37-bb9f-a66271aa3423 RAC1
UN 10.70.6.78 58.13 GB 256 18.3% 94e7f48f-d902-4d4a-9b87-81ccd6aa9e65 RAC1
UN 10.70.47.126 53.89 GB 256 19.4% f36f1f8c-1956-4850-8040-b58273277d83 RAC1
Datacenter: wdc01 (Replication Factor 3)
=================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns Host ID Rack
UN 10.24.116.66 65.81 GB 256 22.1% f9dba004-8c3d-4670-94a0-d301a9b775a8 RAC1
UN 10.55.104.90 63.31 GB 256 21.2% 4746f1bd-85e1-4071-ae5e-9c5baac79469 RAC1
UN 10.55.104.27 62.71 GB 256 21.2% 1a55cfd4-bb30-4250-b868-a9ae13d81ae1 RAC1

nodetool cfstats
Keyspace: KS1
Column Family: CF1
SSTable count: 11
Space used (live): 32769179336
Space used (total): 32769179336
Number of Keys (estimate): 73728
Memtable Columns Count: 1069137
Memtable Data Size: 216442624
Memtable Switch Count: 3
Read Count: 95
Read Latency: NaN ms.
Write Count: 1039417
Write Latency: 0.068 ms.
Bloom Filter False Postives: 345
Bloom Filter False Ratio: 0.00000
Bloom Filter Space Used: 230096
Compacted row minimum size: 150
Compacted row maximum size: 322381140
Compacted row mean size: 2072156

nodetool cfhistograms
$nodetool cfhistograms KS1 CF1
Offset SSTables Write Latency Read Latency Row Size Column Count
1 67264 0 0 0 1331591
2 19512 0 0 0 4241686
3 35529 0 0 0 474784
...
10 10299 1150 0 0 21768
12 5475 3569 0 0 3993135
14 1986 9098 0 0 1434778
17 258 30916 0 0 366895
20 0 52980 0 0 186524
24 0 104463 0 0 25439063
...
179 0 93 1823 1597 1284167
215 0 84 3880 1231655 1147150
258 0 170 5164 209282 956487

nodetool proxyhistograms
$nodetool proxyhistograms
Offset Read Latency Write Latency Range Latency
60 0 15 0
72 0 51 0
86 0 241 0
103 2 2003 0
124 9 5798 0
149 67 7348 0
179 222 6453 0
215 184 6071 0
258 134 5436 0
310 104 4936 0
372 89 4997 0
446 39 6383 0
535 76797 7518 0
642 9364748 96065 0
770 16406421 152663 0
924 7429538 97612 0
1109 6781835 176829 0

JMX via JConsole

JMX via MX4J

JMX via JMXTERM
$ java -jar jmxterm-1.0-alpha-4-uber.jar
Welcome to JMX terminal. Type "help" for available commands.
$>open localhost:7199
#Connection to localhost:7199 is opened
$>bean org.apache.cassandra.db:type=StorageService
#bean is set to org.apache.cassandra.db:type=StorageService
$>info
#mbean = org.apache.cassandra.db:type=StorageService
#class name = org.apache.cassandra.service.StorageService
# attributes
%0 - AllDataFileLocations ([Ljava.lang.String;, r)
%1 - CommitLogLocation (java.lang.String, r)
%2 - CompactionThroughputMbPerSec (int, rw)
...
# operations
%1 - void bulkLoad(java.lang.String p1)
%2 - void clearSnapshot(java.lang.String p1,[Ljava.lang.String; p2)
%3 - void decommission()

JVM Heap Dump via JMAP
jmap -dump:format=b,
file=heap.bin pid

JVM Heap Dump withYourKit

Corrupt SSTable
(Very rare.)

Compaction Error
ERROR [CompactionExecutor:36] 2013-04-29 07:50:49,060 AbstractCassandraDaemon.java
(line 132) Exception in thread Thread[CompactionExecutor:36,1,main]
java.lang.RuntimeException: Last written key
DecoratedKey(138024912283272996716128964353306009224, 6138633035613062
2d616666362d376330612d666531662d373738616630636265396535) >= current key
DecoratedKey(127065377405949402743383718901402082101,
64323962636163652d646561372d333039322d386166322d663064346132363963386131) writing
into *-tmp-hf-7372-Data.db
at
org.apache.cassandra.io.sstable.SSTableWriter.beforeAppend(SSTableWriter.java:134)
at org.apache.cassandra.io.sstable.SSTableWriter.append(SSTableWriter.java:153)
at
org.apache.cassandra.db.compaction.CompactionTask.execute(CompactionTask.java:160)
at
org.apache.cassandra.db.compaction.LeveledCompactionTask.execute(LeveledCompaction
Task.java:50)
at org.apache.cassandra.db.compaction.CompactionManager
$2.runMayThrow(CompactionManager.java:164)

Cause
Change in KeyValidator or
bug in older versions.

Fix
nodetool scrub

Dropped Messages

Logs
MessagingService.java (line 658) 173 READ messages dropped in last 5000ms
StatusLogger.java (line 57) Pool Name Active Pending
StatusLogger.java (line 72) ReadStage 32 284
StatusLogger.java (line 72) RequestResponseStage 1 254
StatusLogger.java (line 72) ReadRepairStage 0 0

nodetool tpstats
Message type Dropped
RANGE_SLICE 0
READ_REPAIR 0
BINARY 0
READ 721
MUTATION 1262
REQUEST_RESPONSE 196

Causes
Excessive GC.
Overloaded IO.
Overloaded Node.
Wide Reads / Large Batches.

High Read Latency

nodetool info
Token : 113427455640312814857969558651062452225
Gossip active : true
Thrift active : true
Load : 291.13 GB
Generation No : 1368569510
Uptime (seconds) : 1022629
Heap Memory (MB) : 5213.01 / 8025.38
Data Center : 1
Rack : 20
Exceptions : 0
Key Cache : size 104857584 (bytes), capacity 104857584 (bytes), 13436862
hits, 16012159 requests, 0.907 recent hit rate, 14400 save period in seconds
Row Cache : size 0 (bytes), capacity 0 (bytes), 0 hits, 0 requests, NaN
recent hit rate, 0 save period in seconds

nodetool cfstats
Column Family: page_views
SSTable count: 17
Space used (live): 289942843592
Space used (total): 289942843592
Number of Keys (estimate): 1071416832
Memtable Columns Count: 2041888
Memtable Data Size: 539015124
Memtable Switch Count: 83
Read Count: 267059
Read Latency: NaN ms.
Write Count: 10516969
Write Latency: 0.054 ms.
Pending Tasks: 0
Bloom Filter False Positives: 128586
Bloom Filter False Ratio: 0.00000
Bloom Filter Space Used: 802906184
Compacted row minimum size: 447
Compacted row maximum size: 3973
Compacted row mean size: 867

nodetool cfhistograms KS1 CF1
1 178437 0 0 0 0
2 20042 0 0 0 0
3 15275 0 0 0 0
4 11632 0 0 0 0
5 4771 0 0 0 0
6 4942 0 0 0 0
7 5540 0 0 0 0
8 4967 0 0 0 0
10 10682 0 0 0 284155
12 8355 0 0 0 15372508
14 1961 0 0 0 137959096
17 322 3 0 0 625733930
20 61 253 0 0 252953547
24 53 15114 0 0 39109718
29 18 255730 0 0 0
35 1 1532619 0 0 0
...

nodetool cfhistograms KS1 CF1
446 0 120 233 0 0
535 0 155 261 21361 0
642 0 127 284 19082720 0
770 0 88 218 498648801 0
924 0 86 2699 504702186 0
1109 0 22 3157 48714564 0
1331 0 18 2818 241091 0
1597 0 15 2155 2165 0
1916 0 19 2098 7 0
2299 0 10 1140 56 0
2759 0 10 1281 0 0
3311 0 6 1064 0 0
3973 0 4 676 3 0
...

jmx-term
$ java -jar jmxterm-1.0-alpha-4-uber.jar
Welcome to JMX terminal. Type "help" for available commands.
$>open localhost:7199
#Connection to localhost:7199 is opened
$>bean org.apache.cassandra.db:columnfamily=CF2,keyspace=KS2,type=ColumnFamilies
#bean is set to
org.apache.cassandra.db:columnfamily=CF2,keyspace=KS2,type=ColumnFamilies
$>get BloomFilterFalseRatio
#mbean =
org.apache.cassandra.db:columnfamily=CF2,keyspace=KS2,type=ColumnFamilies:
BloomFilterFalseRatio = 0.5693801541828607;

Back to cfstats
Column Family: page_views
Read Count: 270075
Bloom Filter False Positives: 131294

Cause
bloom_ﬁlter_fp_chance had been set to 0.1
to reduce memory requirements when
storing 1+ Billion rows per Node.

Fix
Changed read queries to select by column
name to limit SSTables per query.
Long term, migrate to Cassandra v1.2 for off
heap Bloom Filters.

GC Problems

WARN
WARN [ScheduledTasks:1] 2013-03-29 18:40:48,158
GCInspector.java (line 145) Heap is 0.9355130159566108 full.
You may need to reduce memtable and/or cache sizes.
INFO [ScheduledTasks:1] 2013-03-26 16:36:06,383
GCInspector.java (line 122) GC for ConcurrentMarkSweep: 207 ms
for 1 collections, 10105891032 used; max is 13591642112
GCInspector.java (line 122) GC for ParNew: 256 ms for 1
collections, 6504905688 used; max is 13591642112

Serious GC Problems
GCInspector.java (line 122) GC for ParNew: 1115 ms for 1
collections, 9355247296 used; max is 12801015808

Flapping Node
INFO [GossipTasks:1] 2013-03-28 17:42:07,944 Gossiper.java
(line 830) InetAddress /10.1.20.144 is now dead.
INFO [GossipStage:1] 2013-03-28 17:42:54,740 Gossiper.java
(line 816) InetAddress /10.1.20.144 is now UP
INFO [GossipTasks:1] 2013-03-28 17:46:00,585 Gossiper.java
(line 816) InetAddress /10.1.20.144 is now UP

“GC Problems are the result
of workload and
conﬁguration.”
Aaron Morton, Just Now.

Workload Correlation?
Look for wide rows, large
writes, wide reads, un-
bounded multi row reads or
writes.

Compaction Correlation?
Slow down Compaction to improve stability.
concurrent_compactors: 2
compaction_throughput_mb_per_sec: 8
in_memory_compaction_limit_in_mb: 32
(Monitor and reverse when resolved.)

GC Logging Insights
Slow down rate of tenuring and enable full
GC logging.
HEAP_NEWSIZE="1200M"
JVM_OPTS="$JVM_OPTS -XX:SurvivorRatio=4"
JVM_OPTS="$JVM_OPTS -XX:MaxTenuringThreshold=4"

GC’ing Objects in ParNew
- age 1: 8090240 bytes, 8090240 total
- age 2: 565016 bytes, 8655256 total
- age 3: 330152 bytes, 8985408 total
- age 4: 657840 bytes, 9643248 total

GC’ing Objects in ParNew
- age 1: 1315072 bytes, 1315072 total
- age 2: 541072 bytes, 1856144 total
- age 3: 499432 bytes, 2355576 total
- age 4: 316808 bytes, 2672384 total

Cause
Nodes had wide rows & 1.3+
Billion rows and 3+GB of
Bloom Filters.
(Using older bloom_filter_fp_chance of 0.000744.)

Fix
Increased FP chance to 0.1 on
one CF’s and .01 on others.
(One CF reduced from 770MB to 170MB of Bloom Filters.)

Fix
Increased
index_interval from 128
to 512.
(Increased key_cache_size_in_mb to 200.)

Fix
MAX_HEAP_SIZE="8G"
HEAP_NEWSIZE="1000M"
-XX:SurvivorRatio=4"
-XX:MaxTenuringThreshold=2"

Maintenance
Expand to Multi DC

Expand to Multi DC
Update Snitch
Update Replication Strategy
Add Nodes
Update Replication Factor
Rebuild

DC Aware Snitch?
SimpleSnitch puts all
nodes in rack1 and
datacenter1.

More Snitches?
PropertyFileSnitch
RackInferringSnitch

Gossip Based Snitch?
Ec2Snitch
Ec2MultiRegionSnitch
GossipingPropertyFileSnitch*

Changing the Snitch
Do Not change the DC or
Rack for an existing node.
(Cassandra will not be able to ﬁnd your data.)

Moving to the GossipingPropertyFileSnitch
Update cassandra-
topology.properties
on existing nodes with existing DC/Rack
settings for all existing nodes.
Set default to new DC.

Update cassandra-
rackdc.properties
on existing nodes with existing DC/Rack for
the node.

Use a rolling restart to upgrade existing nodes
to GossipingPropertyFileSnitch

Got NTS ?
Must use
NetworkTopologyStrategy
for Multi DC deployments.

SimpleStrategy
Order Token Ranges.
Start with range that contains
Row Key.
Count to RF.

SimpleStrategy
"foo"

Order Token Ranges in the DC.
Start with range that contains the Row Key.
Add ﬁrst unselected Token Range from each
Rack.
Repeat until RF selected.

"foo"
Rack 1
Rack 2Rack 3

NetworkTopologyStrategy & 1 Rack
"foo"
Rack 1

Changing the Replication Strategy
Be Careful if existing
conﬁguration has multiple
Racks.
(Cassandra may not be able to ﬁnd your data.)

Changing the Replication Strategy
Update Keyspace conﬁguration to use
NetworkTopologyStrategy with
datacenter1:3 and new_dc:0.

PreparingThe Client
Disable auto node discovery or use DC
aware methods.
Use LOCAL_QUOURM or EACH_QUOURM.

Conﬁguring New Nodes
Add auto_bootstrap: false to
cassandra.yaml.
Use GossipingPropertyFileSnitch.
Three Seeds from each DC.
(Use cluster_name as a safety.)

Conﬁguring New Nodes
Update cassandra-
rackdc.properties
on new nodes with new DC/Rack for the
node.
(Ignore cassandra-topology.properties)

StartThe New Nodes
New Nodes in the Ring in the
new DC without data or
trafﬁc.

Change the Replication Factor
Update Keyspace conﬁguration to use
NetworkTopologyStrategy with
dataceter1:3 and new_dc:3.

Change the Replication Factor
New DC nodes will start
receiving writes from old DC
coordinators.

Y U No Bootstrap?
DC 1 DC 2

nodetool rebuild DC1
DC 1 DC 2

Rebuild Complete
New Nodes now performing Strong
Consistency reads.
(If EACH_QUOURM used for writes.)

Summary
Relax.
Understand the Platform and
the Tools.
Always maintain Availability.

Aaron Morton
@aaronmorton
Co-Founder & Principal Consultant
Licensed under a Creative Commons Attribution-NonCommercial 3.0 New Zealand License

Cassandra webinars August 2013

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Cassandra webinars August 2013