Troubleshoot SQL execution errors

  After reproducing the SQL execution error, perform the following steps to collect information for troubleshooting.

  1. Execute the following statement to obtain `trace_id`:

     <main id="notice" type='notice'>
     <h4>Notice</h4>
     <p>You must execute the following statement immediately after the SQL statement that causes the error is executed; otherwise, <code>trace_id</code> of the error SQL statement cannot be obtained. </p>
     </main>

     :::tab
     tab MySQL mode

     The following statement is executed to obtain `trace_id` in MySQL mode:

     ```shell
     obclient> SELECT last_trace_id();
     ```

     tab Oracle mode

     The following statement is executed to obtain `trace_id` in Oracle mode:

     ```shell
     obclient> SELECT last_trace_id() FROM DUAL;
     ```

     :::

  2. Obtain the host information based on the obtained `trace_id`.

     Generally, an OceanBase cluster is deployed across multiple nodes. You can execute the following SQL statement to obtain the node that actually executed the SQL statement, and then filter logs based on the node.

     :::tab
     tab MySQL mode

     Execute the following statement in MySQL mode:

     ```shell
     obclient> SELECT * FROM oceanbase.GV$OB_SQL_AUDIT WHERE trace_id=last_trace_id;
     ```

     Replace `last_trace_id` with `trace_id` obtained in the previous step.

     tab Oracle mode

     Execute the following statement in Oracle mode:

     ```shell
     obclient> SELECT * FROM SYS.GV$OB_SQL_AUDIT WHERE trace_id=last_trace_id;
     ```

     Replace `last_trace_id` with `trace_id` obtained in the previous step.

     :::

     Based on the query result in the `GV$OB_SQL_AUDIT` view, the host corresponding to `svr_ip` is the host that actually executed the SQL statement.

  3. Use the `ssh` command to log in to the host based on the obtained host information.

  4. Go to the log directory.

     Taking the installation directory of OceanBase Database, `/home/admin/oceanbase`, as an example. The specific log storage path depends on the actual environment.

     ```shell
     cd /home/admin/oceanbase/log
     ```

  5. Execute the following command to filter relevant logs.

     ```shell
     grep "${trace_id}" observer.log
     ```

     ```shell
     grep "${trace_id}" observer.log.xxx
     ```

     Replace `${trace_id}` with `trace_id` obtained in the previous steps. `observer.log.xxx` is a log file with a timestamp. Replace `xxx` with the actual timestamp in the log file name based on the timestamp when you reproduce the SQL execution error.

  6. Based on the information provided in the logs, analyze the issue based on the error code or error message.

     For more information about logs and error codes, see [Overview of logs](../800.logging/100.logging-overview.md) and [Overview of error information](../../700.reference/500.system-reference/600.error-code-of-mysql-mode/100.use-error-information-of-mysql-mode.md).

     If the information in the logs is unclear, contact technical engineers for assistance.