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Posted to dev@kafka.apache.org by "A. Sophie Blee-Goldman (Jira)" <ji...@apache.org> on 2021/03/25 02:27:00 UTC
[jira] [Resolved] (KAFKA-8042) Kafka Streams creates many segment
stores on state restore
[ https://issues.apache.org/jira/browse/KAFKA-8042?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
A. Sophie Blee-Goldman resolved KAFKA-8042.
-------------------------------------------
Fix Version/s: 2.6.0
Resolution: Fixed
I believe this issue should be solved via https://issues.apache.org/jira/browse/KAFKA-10005 -- most likely the segments you are seeing are due to disabling compaction during the "bulk loading" phase of restoration. This lines up with your observation that upon completion of restoration, the number of files went back down, as we would issue a manual compaction after the bulk loading.
Since 2.6 bulk loading has been removed, so you should not see such large spikes in the number of files since compaction is never disabled
> 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
> Fix For: 2.6.0
>
> 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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