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ClickHouse Java Clients & JDBC Driver
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SESSION_NOT_FOUND error with reconnect to ClickHouse on transactionSupport=true #1372

Open lystor opened 1 year ago

lystor commented 1 year ago

Describe the bug

Hello

Kafka Connect with ClickHouse JDBC driver is used for integration between Kafka and ClickHouse. We have a problem with duplicated records in ClickHouse and decided to enable ClickHouse transactions.

But when transactionSupport=true, Kafka Connect throws SESSION_NOT_FOUND error and reconnects to ClickHouse each time if the delay between inserts is longer than the default_session_timeout.

There are no errors if transactionSupport=false.

Is this the expected behavior?

Is it safe to use ClickHouse transactions on production?

Thank you

Steps to reproduce

Kafka Connect JdbcSinkConfig:

auto.create = false
auto.evolve = false
batch.size = 3000
connection.attempts = 3
connection.backoff.ms = 10000
connection.password = [hidden]
connection.url = jdbc:clickhouse://clickhouse-2.censored.com:8123/deploy_xeen?transactionSupport=true
connection.user = censored
db.timezone = UTC
delete.enabled = false
dialect.name =
fields.whitelist = []
insert.mode = insert
max.retries = 10
mssql.use.merge.holdlock = true
pk.fields = []
pk.mode = none
quote.sql.identifiers = ALWAYS
retry.backoff.ms = 3000
table.name.format = hero_stats
table.types = [TABLE]
trim.sensitive.log = false

Expected behaviour

No errors.

Error log

ClickHouse server:

2023.05.25 14:18:59.991498 [ 625 ] {} <Error> DynamicQueryHandler: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND), Stack trace (when copying this message, always include the lines below):

0. DB::Exception::Exception(DB::Exception::MessageMasked&&, int, bool) @ 0xe1e20b5 in /usr/bin/clickhouse
1. ? @ 0x8a14396 in /usr/bin/clickhouse
2. DB::Session::makeSessionContext(String const&, std::chrono::duration<long long, std::ratio<1l, 1000000000l>>, bool) @ 0x139f369a in /usr/bin/clickhouse
3. DB::HTTPHandler::processQuery(DB::HTTPServerRequest&, DB::HTMLForm&, DB::HTTPServerResponse&, DB::HTTPHandler::Output&, std::optional<DB::CurrentThread::QueryScope>&) @ 0x14972114 in /usr/bin/clickhouse
4. DB::HTTPHandler::handleRequest(DB::HTTPServerRequest&, DB::HTTPServerResponse&) @ 0x14978fee in /usr/bin/clickhouse
5. DB::HTTPServerConnection::run() @ 0x149e7a7d in /usr/bin/clickhouse
6. Poco::Net::TCPServerConnection::start() @ 0x17919874 in /usr/bin/clickhouse
7. Poco::Net::TCPServerDispatcher::run() @ 0x1791aa9b in /usr/bin/clickhouse
8. Poco::PooledThread::run() @ 0x17aa2327 in /usr/bin/clickhouse
9. Poco::ThreadImpl::runnableEntry(void*) @ 0x17a9fd5d in /usr/bin/clickhouse
10. ? @ 0x7f61d3f42b43 in ?
11. clone @ 0x7f61d3fd3bb4 in ?
 (version 23.3.2.37 (official build))
2023.05.25 14:18:59.993352 [ 625 ] {} <Error> DynamicQueryHandler: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND), Stack trace (when copying this message, always include the lines below):

0. DB::Exception::Exception(DB::Exception::MessageMasked&&, int, bool) @ 0xe1e20b5 in /usr/bin/clickhouse
1. ? @ 0x8a14396 in /usr/bin/clickhouse
2. DB::Session::makeSessionContext(String const&, std::chrono::duration<long long, std::ratio<1l, 1000000000l>>, bool) @ 0x139f369a in /usr/bin/clickhouse
3. DB::HTTPHandler::processQuery(DB::HTTPServerRequest&, DB::HTMLForm&, DB::HTTPServerResponse&, DB::HTTPHandler::Output&, std::optional<DB::CurrentThread::QueryScope>&) @ 0x14972114 in /usr/bin/clickhouse
4. DB::HTTPHandler::handleRequest(DB::HTTPServerRequest&, DB::HTTPServerResponse&) @ 0x14978fee in /usr/bin/clickhouse
5. DB::HTTPServerConnection::run() @ 0x149e7a7d in /usr/bin/clickhouse
6. Poco::Net::TCPServerConnection::start() @ 0x17919874 in /usr/bin/clickhouse
7. Poco::Net::TCPServerDispatcher::run() @ 0x1791aa9b in /usr/bin/clickhouse
8. Poco::PooledThread::run() @ 0x17aa2327 in /usr/bin/clickhouse
9. Poco::ThreadImpl::runnableEntry(void*) @ 0x17a9fd5d in /usr/bin/clickhouse
10. ? @ 0x7f61d3f42b43 in ?
11. clone @ 0x7f61d3fd3bb4 in ?
 (version 23.3.2.37 (official build))

Kafka Connect:

[2023-05-25 14:19:00,002] WARN Write of 1 records failed, remainingRetries=10 (io.confluent.connect.jdbc.sink.JdbcSinkTask)
java.sql.SQLException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))
, server ClickHouseNode [uri=http://clickhouse-2.censored.com:8123/deploy_xeen, options={transactionSupport=true}]@1625048275
    at com.clickhouse.jdbc.SqlExceptionUtils.handle(SqlExceptionUtils.java:85)
    at com.clickhouse.jdbc.SqlExceptionUtils.create(SqlExceptionUtils.java:31)
    at com.clickhouse.jdbc.SqlExceptionUtils.handle(SqlExceptionUtils.java:90)
    at com.clickhouse.jdbc.internal.ClickHouseConnectionImpl.getTableColumns(ClickHouseConnectionImpl.java:267)
    at com.clickhouse.jdbc.internal.ClickHouseConnectionImpl.prepareStatement(ClickHouseConnectionImpl.java:843)
    at com.clickhouse.jdbc.ClickHouseConnection.prepareStatement(ClickHouseConnection.java:121)
    at io.confluent.connect.jdbc.dialect.GenericDatabaseDialect.createPreparedStatement(GenericDatabaseDialect.java:368)
    at io.confluent.connect.jdbc.sink.BufferedRecords.add(BufferedRecords.java:138)
    at io.confluent.connect.jdbc.sink.JdbcDbWriter.write(JdbcDbWriter.java:74)
    at io.confluent.connect.jdbc.sink.JdbcSinkTask.put(JdbcSinkTask.java:88)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:587)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:336)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:237)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:206)
    at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:202)
    at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:257)
    at org.apache.kafka.connect.runtime.isolation.Plugins.lambda$withClassLoader$1(Plugins.java:181)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:829)
    Suppressed: java.sql.SQLException: Invalid transaction due to session not found or timed out
        at com.clickhouse.jdbc.SqlExceptionUtils.handle(SqlExceptionUtils.java:85)
        at com.clickhouse.jdbc.internal.JdbcTransaction.rollback(JdbcTransaction.java:63)
        at com.clickhouse.jdbc.internal.ClickHouseConnectionImpl.rollback(ClickHouseConnectionImpl.java:550)
        at io.confluent.connect.jdbc.sink.JdbcDbWriter.write(JdbcDbWriter.java:86)
        ... 13 more
    Caused by: java.io.IOException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))

        at com.clickhouse.client.http.HttpUrlConnectionImpl.checkResponse(HttpUrlConnectionImpl.java:184)
        at com.clickhouse.client.http.HttpUrlConnectionImpl.post(HttpUrlConnectionImpl.java:227)
        at com.clickhouse.client.http.ClickHouseHttpClient.send(ClickHouseHttpClient.java:124)
        at com.clickhouse.client.AbstractClient.sendAsync(AbstractClient.java:161)
        at com.clickhouse.client.AbstractClient.lambda$execute$0(AbstractClient.java:273)
        at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1700)
        ... 3 more
Caused by: java.io.IOException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))

    at com.clickhouse.client.http.HttpUrlConnectionImpl.checkResponse(HttpUrlConnectionImpl.java:184)
    at com.clickhouse.client.http.HttpUrlConnectionImpl.post(HttpUrlConnectionImpl.java:227)
    at com.clickhouse.client.http.ClickHouseHttpClient.send(ClickHouseHttpClient.java:124)
    at com.clickhouse.client.AbstractClient.execute(AbstractClient.java:280)
    at com.clickhouse.client.ClickHouseClientBuilder$Agent.sendOnce(ClickHouseClientBuilder.java:282)
    at com.clickhouse.client.ClickHouseClientBuilder$Agent.send(ClickHouseClientBuilder.java:294)
    at com.clickhouse.client.ClickHouseClientBuilder$Agent.execute(ClickHouseClientBuilder.java:349)
    at com.clickhouse.client.ClickHouseClient.executeAndWait(ClickHouseClient.java:1056)
    at com.clickhouse.client.ClickHouseRequest.executeAndWait(ClickHouseRequest.java:2154)
    at com.clickhouse.jdbc.internal.ClickHouseConnectionImpl.getTableColumns(ClickHouseConnectionImpl.java:264)
    ... 18 more
[2023-05-25 14:19:00,002] INFO Closing connection #1 to Generic (io.confluent.connect.jdbc.util.CachedConnectionProvider)
[2023-05-25 14:19:00,007] INFO Initializing writer using SQL dialect: GenericDatabaseDialect (io.confluent.connect.jdbc.sink.JdbcSinkTask)
[2023-05-25 14:19:00,007] ERROR WorkerSinkTask{id=gone_deploy-xeen_hero_stats-0} RetriableException from SinkTask: (org.apache.kafka.connect.runtime.WorkerSinkTask)
org.apache.kafka.connect.errors.RetriableException: java.sql.SQLException: Exception chain:
java.sql.SQLException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))
, server ClickHouseNode [uri=http://clickhouse-2.censored.com:8123/deploy_xeen, options={transactionSupport=true}]@1625048275
java.io.IOException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))

    at io.confluent.connect.jdbc.sink.JdbcSinkTask.put(JdbcSinkTask.java:114)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.deliverMessages(WorkerSinkTask.java:587)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.poll(WorkerSinkTask.java:336)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.iteration(WorkerSinkTask.java:237)
    at org.apache.kafka.connect.runtime.WorkerSinkTask.execute(WorkerSinkTask.java:206)
    at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:202)
    at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:257)
    at org.apache.kafka.connect.runtime.isolation.Plugins.lambda$withClassLoader$1(Plugins.java:181)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
    at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
    at java.base/java.lang.Thread.run(Thread.java:829)
Caused by: java.sql.SQLException: Exception chain:
java.sql.SQLException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))
, server ClickHouseNode [uri=http://clickhouse-2.censored.com:8123/deploy_xeen, options={transactionSupport=true}]@1625048275
java.io.IOException: Code: 372. DB::Exception: Session not found. (SESSION_NOT_FOUND) (version 23.3.2.37 (official build))

    at io.confluent.connect.jdbc.sink.JdbcSinkTask.getAllMessagesException(JdbcSinkTask.java:159)
    at io.confluent.connect.jdbc.sink.JdbcSinkTask.put(JdbcSinkTask.java:108)
    ... 12 more
[2023-05-25 14:19:00,766] INFO Attempting to open connection #1 to Generic (io.confluent.connect.jdbc.util.CachedConnectionProvider)
[2023-05-25 14:19:00,785] INFO JdbcDbWriter Connected (io.confluent.connect.jdbc.sink.JdbcDbWriter)
[2023-05-25 14:19:00,819] INFO Checking Generic dialect for existence of TABLE "hero_stats" (io.confluent.connect.jdbc.dialect.GenericDatabaseDialect)
[2023-05-25 14:19:00,854] INFO Using Generic dialect TABLE "hero_stats" present (io.confluent.connect.jdbc.dialect.GenericDatabaseDialect)
[2023-05-25 14:19:00,886] INFO Checking Generic dialect for type of TABLE "hero_stats" (io.confluent.connect.jdbc.dialect.GenericDatabaseDialect)

Configuration

Environment

ClickHouse server

3600 60
zhicwu commented 1 year ago

Hi @lystor, AFAIK, transaction support in ClickHouse is still experimental, which means it is not yet ready for production use. However, it is encouraged to use this feature to address integrity issues and provide feedback. I haven't encountered any problems related to this feature causing data corruption or loss, but it is recommended to search the ClickHouse main repository for further evaluation before applying it to your PROD environment.

It appears that there are multiple ClickHouse servers running behind the DNS, and the following events occurred: 1) Kafka Connect asked JDBC driver to start a transaction, hence session was created on server 1 2) Kafka Connect passed a query like insert into ch_table values(?,?,?) to the JDBC driver 3) The JDBC driver attempted to execute a query select * from ch_table where 0 on server 2 (using the same session ID) to determine parameter types(for serializing Java objects in the RowBinary data format) 4) Server 2 reported a session not found error, because the session was created on server 1 and did not exist on server 2

As a workaround, you may want to enable sticky session on your load balancer by checking the session_id parameter in the request URL. Enabling implicit_transaction may help too if the JDBC driver is used in auto-commit mode. However, this is not the case in Kafka Connect, as auto-commit is disabled.

Adding a ClickHouse dialect to Kafka Connect could be beneficial. However, it's not advisable to enhance the driver to support one transaction per query, regardless of whether auto-commit is enabled or not.

lystor commented 1 year ago

Hi @zhicwu, Thank you for your detailed answer.

It appears that there are multiple ClickHouse servers running behind the DNS

Nope. A single ClickHouse Server and a single ClickHouse Keeper are used without any load balancers.

It seems the problem is caused by the JDBC driver.

Full configuration below.

config.xml:

<clickhouse>
    <allow_experimental_transactions>1</allow_experimental_transactions>

    <backups>
        <allowed_disk>backups</allowed_disk>
        <allowed_path>/backups/</allowed_path>
    </backups>

    <grpc remove="remove"></grpc>

    <listen_host remove="remove">::</listen_host>

    <logger replace="replace">
        <console>1</console>
        <level>warning</level>
    </logger>

    <max_partition_size_to_drop>0</max_partition_size_to_drop>
    <max_table_size_to_drop>0</max_table_size_to_drop>

    <mysql_port remove="remove"></mysql_port>

    <postgresql_port remove="remove"></postgresql_port>

    <prometheus>
        <asynchronous_metrics>true</asynchronous_metrics>
        <endpoint>/metrics</endpoint>
        <events>true</events>
        <metrics>true</metrics>
        <port>9187</port>
        <status_info>true</status_info>
    </prometheus>

    <storage_configuration>
        <disks>
            <backups>
                <type>local</type>
                <path>/backups/</path>
            </backups>
        </disks>
    </storage_configuration>

    <zookeeper>
        <node>
            <host>clickhouse-2.censored.local</host>
            <port>9181</port>
        </node>
    </zookeeper>
</clickhouse>

keeper_config.xml:

<clickhouse>
    <listen_host>0.0.0.0</listen_host>

    <logger replace="replace">
        <console>1</console>
        <level>warning</level>
    </logger>

    <keeper_server>
            <tcp_port>9181</tcp_port>

            <server_id>1</server_id>

            <raft_configuration replace="replace">
                <server>
                    <id>1</id>
                    <hostname>clickhouse-2.censored.local</hostname>
                    <port>9234</port>
                </server>
            </raft_configuration>
    </keeper_server>
</clickhouse>

users.xml:

<clickhouse>
    <profiles>
        <default>
            <allow_introspection_functions>1</allow_introspection_functions>
        </default>
    </profiles>

    <users>
        <default>
            <access_management>1</access_management>
            <named_collection_control>1</named_collection_control>
            <show_named_collections>1</show_named_collections>
            <show_named_collections_secrets>1</show_named_collections_secrets>

            <networks replace="replace">
                <ip>127.0.0.1</ip>
            </networks>
        </default>
    </users>
</clickhouse>

initdb.sql:

CREATE USER IF NOT EXISTS censored IDENTIFIED BY 'censored';
GRANT SELECT ON *.* TO censored;
GRANT INSERT ON *.* TO censored;

docker-compose.yml:

version: "3.8"

services:
  keeper:
    command:
      - /usr/bin/clickhouse-keeper
      - --config-file=/etc/clickhouse-keeper/keeper_config.xml
    image: clickhouse/clickhouse-keeper:23.3.2.37
    logging:
      options:
        max-size: 10m
        max-file: "2"
    network_mode: host
    ports:
      - "9181:9181"
      - "9234:9234"
    restart: unless-stopped
    ulimits:
      memlock:
        soft: -1
        hard: -1
      nofile:
        soft: 65000
        hard: 65000
    user: clickhouse
    volumes:
      - ./keeper/keeper_config.xml:/etc/clickhouse-keeper/keeper_config.d/censored.xml:ro
      - /data/clickhouse/keeper:/var/lib/clickhouse

  server:
    cap_add:
      - IPC_LOCK
      - NET_ADMIN
      - SYS_NICE
    image: clickhouse/clickhouse-server:23.3.2.37
    logging:
      options:
        max-size: 10m
        max-file: "2"
    network_mode: host
    ports:
      - "8123:8123"
      - "9000:9000"
      - "9187:9187"
    restart: unless-stopped
    ulimits:
      memlock:
        soft: -1
        hard: -1
      nofile:
        soft: 65000
        hard: 65000
    user: clickhouse
    volumes:
      - ./server/config.xml:/etc/clickhouse-server/config.d/censored.xml:ro
      - ./server/initdb.sql:/docker-entrypoint-initdb.d/initdb.sql:ro
      - ./server/users.xml:/etc/clickhouse-server/users.d/censored.xml:ro
      - /data/clickhouse/server:/var/lib/clickhouse
      - backups:/backups

volumes:
  backups:
    driver_opts:
      type: "nfs"
      o: "addr=backup-1.censored.local,intr,nfsvers=4.1,noatime,nodiratime,soft"
      device: "backup-1.censored.local:/data/clickhouse"

kafka-connect Dockerfile:

FROM confluentinc/cp-kafka-connect-base:7.4.0

ENV CONNECT_PLUGIN_PATH="/usr/share/java,/usr/share/confluent-hub-components"

RUN set -ex \
    && confluent-hub install --no-prompt confluentinc/kafka-connect-avro-converter:7.4.0 \
    && confluent-hub install --no-prompt confluentinc/kafka-connect-jdbc:10.7.0 \
    && cd /usr/share/confluent-hub-components/confluentinc-kafka-connect-jdbc/lib \
    && curl -fsLO https://github.com/ClickHouse/clickhouse-java/releases/download/v0.4.6/clickhouse-jdbc-0.4.6-shaded.jar

kafka-connect StatefulSet:

  ...
      containers:
      - env:
        - name: CONNECT_BOOTSTRAP_SERVERS
          value: kafka-1-dev-ps.censored.com:9092
        - name: CONNECT_CONFIG_STORAGE_REPLICATION_FACTOR
          value: "1"
        - name: CONNECT_CONFIG_STORAGE_TOPIC
          value: gone_deploy-xeen_kafka-connect-config
        - name: CONNECT_GROUP_ID
          value: deploy-xeen
        - name: CONNECT_KEY_CONVERTER
          value: io.confluent.connect.avro.AvroConverter
        - name: CONNECT_KEY_CONVERTER_SCHEMA_REGISTRY_URL
          value: http://kafka-1-dev-ps.censored.com:8081
        - name: CONNECT_OFFSET_STORAGE_REPLICATION_FACTOR
          value: "1"
        - name: CONNECT_OFFSET_STORAGE_TOPIC
          value: gone_deploy-xeen_kafka-connect-offset
        - name: CONNECT_REST_ADVERTISED_HOST_NAME
          valueFrom:
            fieldRef:
              apiVersion: v1
              fieldPath: status.podIP
        - name: CONNECT_REST_PORT
          value: "8083"
        - name: CONNECT_STATUS_STORAGE_REPLICATION_FACTOR
          value: "1"
        - name: CONNECT_STATUS_STORAGE_TOPIC
          value: gone_deploy-xeen_kafka-connect-status
        - name: CONNECT_VALUE_CONVERTER
          value: io.confluent.connect.avro.AvroConverter
        - name: CONNECT_VALUE_CONVERTER_SCHEMA_REGISTRY_URL
          value: http://kafka-1-dev-ps.censored.com:8081
        - name: KAFKA_HEAP_OPTS
          value: -Xms512M -Xmx512M
        - name: KAFKA_JMX_OPTS
          value: -javaagent:/usr/share/java/cp-base-new/jmx_prometheus_javaagent-0.18.0.jar=9187:/etc/kafka-connect-exporter/config.yml
        image: artifactory-1.censored.com/kafka-connect:xeen-4504
        name: kafka-connect
...
zhicwu commented 1 year ago

Thank you, @lystor, for providing additional details about the environment.

The transaction depends on the session to function properly. Therefore, if an insert operation takes longer than the default session timeout, the transaction will be rolled back on the server, and the client will receive a "session not found" error. Have you attempted to increase the values of transaction_timeout or session_timeout (in seconds) in the JDBC connection string? Alternatively, you can consider increasing the value of default_session_timeout in the server configuration.

I will improve the error message to make it less confusing for others.

lystor commented 1 year ago

Therefore, if an insert operation takesis reproduced longer than the default session timeout.

We don't have such long transactions.

The bug has 100% reproduction rate on new idle server without any workload and active users even on insert of single row.

STR: delay between events in kafka longer than max_session_timeout.

The server's configuration is provided below.

zhicwu commented 1 year ago

delay between events in kafka longer than max_session_timeout.

I see. Actually, the transaction begins when jdbcConnection.setAutoCommit(false) is called. After either a commit() or a rollback() operation, the current transaction is closed, and a new transaction is initiated.

Perhaps it would be preferable to delay initiating the transaction until the first query is executed. In the meantime, as a workaround, you can increase the values of transaction_timeout or session_timeout in connection string.

lystor commented 1 year ago

@zhicwu , thank you for the workaround.

Last question: are you going to make some fixes in the JDBC-driver to remove this annoying and useless DB::Exception: Session not found from logs?

Or this is the expected behavior, and users have to accept and live with these errors in the logs on both client and ClickHouse server sides?

zhicwu commented 1 year ago

The current behavior is as expected, although it can be confusing. Nevertheless, there is room for improvement in terms of usability. It is uncertain whether session and transaction will be decoupled in the future. However, for the Java library, I am contemplating implementing two modifications:

Let's keep this issue as open until the necessary changes have been implemented.