How to decrease the number of partitions?

Issue

• How to decrease the number of partitions?
• "2396093: Failure processing KafkaTopic watch event MODIFIED on resource my-topic with labels {strimzi.io/cluster=my-cluster}: Number of partitions cannot be decreased" error occurs

[2020-12-25 05:03:52,505] INFO  <TopicWatcher:43> [2.25.0.1/...] 32|kube =my-topic|2396093: event MODIFIED on resource my-topic generation=3, labels={strimzi.io/cluster=my-cluster}
[2020-12-25 05:03:52,548] INFO  <opicOperator:536> [oop-thread-0] 32|kube =my-topic|2396093: Reconciling topic my-topic, k8sTopic:nonnull, kafkaTopic:nonnull, privateTopic:nonnull
[2020-12-25 05:03:52,549] ERROR <opicOperator:691> [oop-thread-0] 32|kube =my-topic|2396093: Number of partitions cannot be decreased
[2020-12-25 05:03:52,590] INFO  <opicOperator:120> [oop-thread-0] Number of partitions cannot be decreased
[2020-12-25 05:03:52,600] INFO  <TopicWatcher:43> [2.25.0.1/...] 33|kube =my-topic|2396095: event MODIFIED on resource my-topic generation=3, labels={strimzi.io/cluster=my-cluster}
[2020-12-25 05:03:52,612] ERROR <TopicWatcher:56> [oop-thread-0] 32|kube =my-topic|2396093: Failure processing KafkaTopic watch event MODIFIED on resource my-topic with labels {strimzi.io/cluster=my-cluster}: Number of partitions cannot be decreased
io.strimzi.operator.topic.PartitionDecreaseException: Number of partitions cannot be decreased
     at io.strimzi.operator.topic.TopicOperator.update3Way(TopicOperator.java:694) ~[io.strimzi.topic-operator-0.20.0.redhat-00003.jar:0.20.0.redhat-00003]
     at io.strimzi.operator.topic.TopicOperator.reconcile(TopicOperator.java:597) ~[io.strimzi.topic-operator-0.20.0.redhat-00003.jar:0.20.0.redhat-00003]
     at io.strimzi.operator.topic.TopicOperator.lambda$reconcileOnResourceChange$24(TopicOperator.java:1062) ~[io.strimzi.topic-operator-0.20.0.redhat-00003.jar:0.20.0.redhat-00003]
     at io.vertx.core.Future.lambda$compose$3(Future.java:368) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.handle(FutureImpl.java:176) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.doComplete(CompositeFutureImpl.java:252) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.tryComplete(CompositeFutureImpl.java:227) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.tryComplete(CompositeFutureImpl.java:232) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.complete(CompositeFutureImpl.java:199) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.lambda$all$0(CompositeFutureImpl.java:39) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.Future.lambda$map$4(Future.java:416) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.Future.lambda$recover$6(Future.java:495) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.Future.lambda$map$4(Future.java:416) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.handle(FutureImpl.java:176) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.doComplete(CompositeFutureImpl.java:252) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.tryComplete(CompositeFutureImpl.java:227) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.tryComplete(CompositeFutureImpl.java:232) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.complete(CompositeFutureImpl.java:199) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.CompositeFutureImpl.lambda$all$0(CompositeFutureImpl.java:39) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.dispatch(FutureImpl.java:105) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.tryComplete(FutureImpl.java:150) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.FutureImpl.complete(FutureImpl.java:111) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.strimzi.operator.topic.KafkaImpl.lambda$mapFuture$7(KafkaImpl.java:168) ~[io.strimzi.topic-operator-0.20.0.redhat-00003.jar:0.20.0.redhat-00003]
     at io.vertx.core.impl.ContextImpl.executeTask(ContextImpl.java:366) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.vertx.core.impl.EventLoopContext.lambda$executeAsync$0(EventLoopContext.java:38) ~[io.vertx.vertx-core-3.9.4.redhat-00001.jar:3.9.4.redhat-00001]
     at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:164) [io.netty.netty-common-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:472) [io.netty.netty-common-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:500) [io.netty.netty-transport-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989) [io.netty.netty-common-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) [io.netty.netty-common-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) [io.netty.netty-common-4.1.50.Final-redhat-00001.jar:4.1.50.Final-redhat-00001]
     at java.lang.Thread.run(Thread.java:834) [?:?]