Help Center > > Developer Guide> Query Performance Optimization> Troubleshooting Errors Using SQL Statements> Automatic Retry upon SQL Statement Execution Errors

Automatic Retry upon SQL Statement Execution Errors

Updated at: Jul 15, 2020 GMT+08:00

With automatic retry (referred to as CN retry), DWS retries an SQL statement when the execution of this statement fails. If an SQL statement sent from the gsql client, JDBC driver, or ODBC driver fails to be executed, the CN can automatically identify the error reported during execution and re-deliver the task to retry.

The restrictions of this function are as follows:

  • Functionality restrictions:
    • CN retry increases execution success rate but does not guarantee success.
    • CN retry is enabled by default. In this case, the system records logs about temporary tables. If it is disabled, the system will not record the logs. Therefore, do not repeatedly enable and disable CN retry when temporary tables are used. Otherwise, data inconsistency may occur after a CN retry following a primary/standby switchover.
    • CN retry is enabled by default. In this case, the unlogged keyword is ignored in the statement for creating unlogged tables and thereby ordinary tables will be created by using this statement. If CN retry is disabled, the system records logs about unlogged tables. Therefore, do not repeatedly enable and disable CN retry when unlogged tables are used. Otherwise, data inconsistency may occur after a CN retry following a primary/standby switchover.
    • When GDS is used to export data, CN retry is supported. The existing mechanism checks for duplicate files and deletes duplicate files during data export. Therefore, you are advised not to repeatedly export data for the same foreign table unless you are sure that files with the same name in the data directory need to be deleted.
  • Error type restrictions:

    Only the error types in Table 1 are supported.

  • Statement type restrictions:

    Support single-statement CN retry, stored procedures, functions, and anonymous blocks. Statements in transaction blocks are not supported.

  • Statement restrictions of a stored procedure:
    • If an error occurs during the execution of a stored procedure containing EXCEPTION (including statement block execution and statement execution in EXCEPTION), the stored procedure can be retried. If the error is captured by EXCEPTION, the stored procedure cannot be retried.
    • Packages that use global variables are not supported.
    • DBMS_JO is not supported.
    • UTL_FILE is not supported.
  • Cluster status restrictions:
    • Only DNs or GTMs are faulty.
    • The cluster can be recovered before the number of CN retries reaches the allowed maximum (controlled by max_query_retry_times). Otherwise, CN retry may fail.
    • CN retry is not supported during scale-out.
  • Data import restrictions:
    • The COPY FROM STDIN statement is not supported.
    • The gsql \copy from metacommand is not supported.
    • JDBC CopyManager copyIn is not supported.

Table 1 lists the error types supported by CN retry and the corresponding error codes. You can use the GUC parameter retry_ecode_list to set the list of error types supported by CN retry. You are not advised to modify this parameter. To modify it, contact Huawei technical support.

Table 1 Error types supported by CN retry

Error Type

Error Code

Remarks

CONNECTION_RESET_BY_PEER

YY001

TCP communication errors: Connection reset by peer (communication between the CN and DNs)

STREAM_CONNECTION_RESET_BY_PEER

YY002

TCP communication errors: Stream connection reset by peer (communication between DNs)

LOCK_WAIT_TIMEOUT

YY003

Lock wait timeout

CONNECTION_TIMED_OUT

YY004

TCP communication errors: Connection timed out

SET_QUERY_ERROR

YY005

Failed to deliver the SET command: Set query

OUT_OF_LOGICAL_MEMORY

YY006

Failed to apply for memory: Out of logical memory

SCTP_MEMORY_ALLOC

YY007

SCTP communication errors: Memory allocate error

SCTP_NO_DATA_IN_BUFFER

YY008

SCTP communication errors: SCTP no data in buffer

SCTP_RELEASE_MEMORY_CLOSE

YY009

SCTP communication errors: Release memory close

SCTP_TCP_DISCONNECT

YY010

SCTP communication errors: TCP disconnect

SCTP_DISCONNECT

YY011

SCTP communication errors: SCTP disconnect

SCTP_REMOTE_CLOSE

YY012

SCTP communication errors: Stream closed by remote

SCTP_WAIT_POLL_UNKNOW

YY013

Waiting for an unknown poll: SCTP wait poll unknown

SNAPSHOT_INVALID

YY014

Snapshot invalid

ERRCODE_CONNECTION_RECEIVE_WRONG

YY015

Connection receive wrong

OUT_OF_MEMORY

53200

Out of memory

CONNECTION_FAILURE

08006

GTM errors: Connection failure

CONNECTION_EXCEPTION

08000

Failed to communicate with DNs due to connection errors: Connection exception

ADMIN_SHUTDOWN

57P01

System shutdown by administrators: Admin shutdown

STREAM_REMOTE_CLOSE_SOCKET

XX003

Remote socket disabled: Stream remote close socket

ERRCODE_STREAM_DUPLICATE_QUERY_ID

XX009

Duplicate query id

ERRCODE_STREAM_CONCURRENT_UPDATE

YY016

Stream concurrent update

To enable CN retry, set the following GUC parameters:
  • Mandatory GUC parameters (required by both CNs and DNs)

    max_query_retry_times. For details, see max_query_retry_times.

    If CN retry is enabled, temporary table data is logged. For data consistency, do not switch the enabled/disabled status (for details, see max_query_retry_times) for CN retry when the temporary tables are being used by sessions.

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