运行命令：
`λ oc exec -it ms-ksql-db-server-deployment-76f454b75-mjfbh bash`
[appuser@ms-ksql-db-server-deployment-76f454b75-mjfbh ~]$ `ksql`
OpenJDK 64-Bit Server VM warning: Option UseConcMarkSweepGC was deprecated in version 9.0 and will likely be removed in a future release.
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= | | _____ __ _| | _ \| __ ) =
= | |/ / __|/ _` | | | | | _ \ =
= | <\__ \ (_| | | |_| | |_) | =
= |_|\_\___/\__, |_|____/|____/ =
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= The Database purpose-built =
= for stream processing apps =
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Copyright 2017-2022 Confluent Inc.
CLI v0.26.0, Server v0.26.0 located at http://localhost:8088
Server Status: RUNNING
Having trouble? Type 'help' (case-insensitive) for a rundown of how things work!
ksql> CREATE STREAM CLIENT_STREAM WITH (KAFKA_TOPIC='private-import-clients',VALUE_FORMAT='AVRO');
Message
----------------
Stream created
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ksql> SET 'auto.offset.reset'='earliest';
Successfully changed local property 'auto.offset.reset' to 'earliest'. Use the UNSET command to revert your change.
ksql> SHOW STREAMS;
Stream Name | Kafka Topic | Key Format | Value Format | Windowed
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CLIENT_STREAM | private-import-clients | KAFKA | AVRO | false
KSQL_PROCESSING_LOG | default_ksql_processing_log | KAFKA | JSON | false
------------------------------------------------------------------------------------------
ksql> SELECT * FROM CLIENT_STREAM EMIT CHANGES;我正在从一个主题 private-import-clients 编写 KSQL Streams，我假设我创建的 Stream 的结果将给 origin 一个主题 CLIENT_STREAM 或其他名称。这是对的吗？如果是这样，KSQL stores 那个主题 CLIENT_STREAM 在哪里？我有一个 Spring 启动应用程序，它将使用主题 CLIENT_STREAM 。
回答1
CREATE STREAM 语句是 DDL 语句，因此操作是更新 ksqlDB 元数据。
每个 ksqlDB 服务器都有一个内部的内存中元数据 store 或元存储，它在接收 DDL 语句时构建。 Metastore 是内存中的 map。对于每个新的 DDL 语句，ksqlDB 引擎都会向元存储添加一个条目。
ksqlDB 引擎将 DML 语句转换为 Kafka Streams 应用程序
https://docs.ksqldb.io/en/latest/operate-and-deploy/how-it-works/解释了 KSQL 如何创建逻辑、物理计划以及它如何处理查询。
因此它 stores 仅用于 DDL 语句的内存中 map 中的本地元数据，其行为类似于 DML 语句的流。