Adrian McCague created KAFKA-8042:
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Summary: 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: 2.1.1, 2.1.0
Reporter: Adrian McCague
Attachments: StateStoreSegments-StreamsConfig.txt
Note that this 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.
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):
{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
{code}
Once re-balancing and state restoration is complete - the redundant segment
files are deleted and the segment count drops to 508.
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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