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https://issues.apache.org/jira/browse/KAFKA-8042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16802020#comment-16802020
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Adrian McCague commented on KAFKA-8042:
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This definitely applies to the 2.1 release.
KAFKA-7934 does look like a path to avoid this issue, but I feel like there is
another problem here with regard to the number of segments being created and
not removed. It appears the total number that could be created during
rebalancing is arbitrary, implying to me that there is a degree of redundancy
here. As it stands moving to this version introduces a risk of filling up our
state volumes.
> Kafka Streams creates many segment stores on state restore
> ----------------------------------------------------------
>
> Key: KAFKA-8042
> URL: https://issues.apache.org/jira/browse/KAFKA-8042
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.1.0, 2.1.1
> Reporter: Adrian McCague
> Priority: Major
> Attachments: StateStoreSegments-StreamsConfig.txt
>
>
> Note that this is from the perspective of one instance of an application,
> where there are 8 instances total, with partition count 8 for all topics and
> of course stores. Standby replicas = 1.
> In the process there are multiple instances of {{KafkaStreams}} so the below
> detail is from one of these.
> h2. Actual Behaviour
> During state restore of an application, many segment stores are created (I am
> using MANIFEST files as a marker since they preallocate 4MB each). As can be
> seen this topology has 5 joins - which is the extent of its state.
> {code:java}
> bash-4.2# pwd
> /data/fooapp/0_7
> bash-4.2# for dir in $(find . -maxdepth 1 -type d); do echo "${dir}: $(find
> ${dir} -type f -name 'MANIFEST-*' -printf x | wc -c)"; done
> .: 8058
> ./KSTREAM-JOINOTHER-0000000025-store: 851
> ./KSTREAM-JOINOTHER-0000000040-store: 819
> ./KSTREAM-JOINTHIS-0000000024-store: 851
> ./KSTREAM-JOINTHIS-0000000029-store: 836
> ./KSTREAM-JOINOTHER-0000000035-store: 819
> ./KSTREAM-JOINOTHER-0000000030-store: 819
> ./KSTREAM-JOINOTHER-0000000045-store: 745
> ./KSTREAM-JOINTHIS-0000000039-store: 819
> ./KSTREAM-JOINTHIS-0000000044-store: 685
> ./KSTREAM-JOINTHIS-0000000034-store: 819
> There are many (x800 as above) of these segment files:
> ./KSTREAM-JOINOTHER-0000000025-store.1551466290000
> ./KSTREAM-JOINOTHER-0000000025-store.1551559020000
> ./KSTREAM-JOINOTHER-0000000025-store.1551492690000
> ./KSTREAM-JOINOTHER-0000000025-store.1551548790000
> ./KSTREAM-JOINOTHER-0000000025-store.1551698610000
> ./KSTREAM-JOINOTHER-0000000025-store.1551530640000
> ./KSTREAM-JOINOTHER-0000000025-store.1551484440000
> ./KSTREAM-JOINOTHER-0000000025-store.1551556710000
> ./KSTREAM-JOINOTHER-0000000025-store.1551686730000
> ./KSTREAM-JOINOTHER-0000000025-store.1551595650000
> ./KSTREAM-JOINOTHER-0000000025-store.1551757350000
> ./KSTREAM-JOINOTHER-0000000025-store.1551685740000
> ./KSTREAM-JOINOTHER-0000000025-store.1551635250000
> ./KSTREAM-JOINOTHER-0000000025-store.1551652410000
> ./KSTREAM-JOINOTHER-0000000025-store.1551466620000
> ./KSTREAM-JOINOTHER-0000000025-store.1551781770000
> ./KSTREAM-JOINOTHER-0000000025-store.1551587400000
> ./KSTREAM-JOINOTHER-0000000025-store.1551681450000
> ./KSTREAM-JOINOTHER-0000000025-store.1551662310000
> ./KSTREAM-JOINOTHER-0000000025-store.1551721710000
> ./KSTREAM-JOINOTHER-0000000025-store.1551750750000
> ./KSTREAM-JOINOTHER-0000000025-store.1551630960000
> ./KSTREAM-JOINOTHER-0000000025-store.1551615120000
> ./KSTREAM-JOINOTHER-0000000025-store.1551792330000
> ./KSTREAM-JOINOTHER-0000000025-store.1551462660000
> ./KSTREAM-JOINOTHER-0000000025-store.1551536910000
> ./KSTREAM-JOINOTHER-0000000025-store.1551592350000
> ./KSTREAM-JOINOTHER-0000000025-store.1551527340000
> ./KSTREAM-JOINOTHER-0000000025-store.1551606870000
> ./KSTREAM-JOINOTHER-0000000025-store.1551744150000
> ./KSTREAM-JOINOTHER-0000000025-store.1551508200000
> ./KSTREAM-JOINOTHER-0000000025-store.1551486420000
> ... etc
> {code}
> Once re-balancing and state restoration is complete - the redundant segment
> files are deleted and the segment count drops to 508 total (where the above
> mentioned state directory is one of many).
> We have seen the number of these segment stores grow to as many as 15000 over
> the baseline 508 which can fill smaller volumes. *This means that a state
> volume that would normally have ~300MB total disk usage would use in excess
> of 30GB during rebalancing*, mostly preallocated MANIFEST files.
> h2. Expected Behaviour
> For this particular application we expect 508 segment folders total to be
> active and existing throughout rebalancing. Give or take migrated tasks that
> are subject to the {{state.cleanup.delay.ms}}.
> h2. Preliminary investigation
> * This does not appear to be the case in v1.1.0. With our application the
> number of state directories only grows to 670 (over the base line 508)
> * The MANIFEST files were not preallocated to 4MB in v1.1.0 they are now in
> v2.1.x, this appears to be expected RocksDB behaviour, but exacerbates the
> many segment stores.
> * Suspect https://github.com/apache/kafka/pull/5253 to be the source of this
> change of behaviour.
> A workaround is to use {{rocksdb.config.setter}} and set the preallocated
> amount for MANIFEST files to a lower value such as 64KB, however the number
> of segment stores appears to be unbounded so disk volumes may still fill up
> for a heavier application.
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