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TiDB Lightning Error Resolution

Starting from v5.4.0, you can configure TiDB Lightning to skip errors like invalid type conversion and unique key conflicts, and to continue the data processing as if those wrong row data does not exist. A report will be generated for you to read and manually fix errors afterward. This is ideal for importing from a slightly dirty data source, where locating the errors manually is difficult and restarting TiDB Lightning on every encounter is costly.

This document introduces TiDB Lightning error types, how to query the errors, and provides an example. The following configuration items are involved:

  • lightning.max-error: the tolerance threshold of type error
  • conflict.strategy, conflict.threshold, and conflict.max-record-rows: configurations related to conflicting data
  • tikv-importer.duplicate-resolution (deprecated in v8.0.0 and will be removed in a future release): the conflict handling configuration that can only be used in the physical import mode
  • lightning.task-info-schema-name: the database where conflicting data is stored when TiDB Lightning detects conflicts

For more information, see TiDB Lightning (Task).

Type error

You can use the lightning.max-error configuration to increase the tolerance of errors related to data types. If this configuration is set to N, TiDB Lightning allows and skips up to N type errors from the data source before it exists. The default value 0 means that no error is allowed.

These errors are recorded in a database. After the import is completed, you can view the errors in the database and process them manually. For more information, see Error Report.

[lightning] max-error = 0

The above configuration covers the following errors:

  • Invalid values (example: set 'Text' to an INT column).
  • Numeric overflow (example: set 500 to a TINYINT column)
  • String overflow (example: set 'Very Long Text' to a VARCHAR(5) column).
  • Zero date-time (namely '0000-00-00' and '2021-12-00').
  • Set NULL to a NOT NULL column.
  • Failed to evaluate a generated column expression.
  • Column count mismatch. The number of values in the row does not match the number of columns of the table.
  • Any other SQL errors.

The following errors are always fatal, and cannot be skipped by changing lightning.max-error:

  • Syntax error (such as unclosed quotation marks) in the original CSV, SQL or Parquet file.
  • I/O, network or system permission errors.

Conflict errors

You can use the conflict.threshold configuration item to increase the tolerance of errors related to data conflict. If this configuration item is set to N, TiDB Lightning allows and skips up to N conflict errors from the data source before it exits. The default value is 10000, which means that 10000 errors are tolerant.

These errors are recorded in a table. After the import is completed, you can view the errors in the database and process them manually. For more information, see Error Report

Error report

If TiDB Lightning encounters errors during the import, it outputs a statistics summary about these errors in both your terminal and the log file when it exits.

  • The error report in the terminal is similar to the following table:

    #ERROR TYPEERROR COUNTERROR DATA TABLE
    1Data Type1000lightning_task_info.type_error_v1
  • The error report in the TiDB Lightning log file is as follows:

    [2022/03/13 05:33:57.736 +08:00] [WARN] [errormanager.go:459] ["Detect 1000 data type errors in total, please refer to table `lightning_task_info`.`type_error_v1` for more details"]

All errors are written to tables in the lightning_task_info database in the downstream TiDB cluster. After the import is completed, if the error data is collected, you can view the errors in the database and process them manually.

You can change the database name by configuring lightning.task-info-schema-name.

[lightning] task-info-schema-name = 'lightning_task_info'

TiDB Lightning creates 3 tables in this database:

CREATE TABLE type_error_v1 ( task_id bigint NOT NULL, create_time datetime(6) NOT NULL DEFAULT now(6), table_name varchar(261) NOT NULL, path varchar(2048) NOT NULL, offset bigint NOT NULL, error text NOT NULL, row_data text NOT NULL ); CREATE TABLE conflict_error_v1 ( task_id bigint NOT NULL, create_time datetime(6) NOT NULL DEFAULT now(6), table_name varchar(261) NOT NULL, index_name varchar(128) NOT NULL, key_data text NOT NULL, row_data text NOT NULL, raw_key mediumblob NOT NULL, raw_value mediumblob NOT NULL, raw_handle mediumblob NOT NULL, raw_row mediumblob NOT NULL, KEY (task_id, table_name) ); CREATE TABLE conflict_records ( task_id bigint NOT NULL, create_time datetime(6) NOT NULL DEFAULT now(6), table_name varchar(261) NOT NULL, path varchar(2048) NOT NULL, offset bigint NOT NULL, error text NOT NULL, row_id bigint NOT NULL COMMENT 'the row id of the conflicting row', row_data text NOT NULL COMMENT 'the row data of the conflicting row', KEY (task_id, table_name) );

type_error_v1 records all type errors managed by lightning.max-error. Each error corresponds to one row.

conflict_error_v2 records conflicts managed by the conflict configuration group in the physical import mode. Each pair of conflicts corresponds to two rows.

conflict_records records conflicts managed by the conflict configuration group in both the logical import mode and physical import mode. Each error corresponds to one row.

ColumnSyntaxTypeConflictDescription
task_idThe TiDB Lightning task ID that generates this error
create_timeThe time at which the error is recorded
table_nameThe name of the table that contains the error, in the form of '`db`.`tbl`'
pathThe path of the file that contains the error
offsetThe byte position in the file where the error is found
errorThe error message
contextThe text that surrounds the error
index_nameThe name of the unique key in conflict. It is 'PRIMARY' for primary key conflicts.
key_dataThe formatted key handle of the row that causes the error. The content is for human reference only, and not intended to be machine-readable.
row_dataThe formatted row data that causes the error. The content is for human reference only, and not intended to be machine-readable
raw_keyThe key of the conflicted KV pair
raw_valueThe value of the conflicted KV pair
raw_handleThe row handle of the conflicted row
raw_rowThe encoded value of the conflicted row

Example

In this example, a data source is prepared with some known errors.

  1. Prepare the database and table schema.

    mkdir example && cd example echo 'CREATE SCHEMA example;' > example-schema-create.sql echo 'CREATE TABLE t(a TINYINT PRIMARY KEY, b VARCHAR(12) NOT NULL UNIQUE);' > example.t-schema.sql
  2. Prepare the data.

    cat <<EOF > example.t.1.sql INSERT INTO t (a, b) VALUES (0, NULL), -- column is NOT NULL (1, 'one'), (2, 'two'), (40, 'forty'), -- conflicts with the other 40 below (54, 'fifty-four'), -- conflicts with the other 'fifty-four' below (77, 'seventy-seven'), -- the string is longer than 12 characters (600, 'six hundred'), -- the number overflows TINYINT (40, 'forty'), -- conflicts with the other 40 above (42, 'fifty-four'); -- conflicts with the other 'fifty-four' above EOF
  3. Configure TiDB Lightning to enable strict SQL mode, use the Local-backend to import data, replace duplicates, and skip up to 10 errors.

    cat <<EOF > config.toml [lightning] max-error = 10 [tikv-importer] backend = 'local' sorted-kv-dir = '/tmp/lightning-tmp/' [conflict] strategy = 'replace' [mydumper] data-source-dir = '.' [tidb] host = '127.0.0.1' port = 4000 user = 'root' password = '' sql-mode = 'STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE' EOF
  4. Run TiDB Lightning. This command will exit successfully because all errors are skipped.

    tiup tidb-lightning -c config.toml
  5. Verify that the imported table only contains the two normal rows:

    $ mysql -u root -h 127.0.0.1 -P 4000 -e 'select * from example.t' +---+-----+ | a | b | +---+-----+ | 1 | one | | 2 | two | +---+-----+
  6. Check whether the type_error_v1 table has caught the three rows involving type conversion:

    $ mysql -u root -h 127.0.0.1 -P 4000 -e 'select * from lightning_task_info.type_error_v1;' -E *************************** 1. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.620090 table_name: `example`.`t` path: example.t.1.sql offset: 46 error: failed to cast value as varchar(12) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin for column `b` (#2): [table:1048]Column 'b' cannot be null row_data: (0,NULL) *************************** 2. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.627496 table_name: `example`.`t` path: example.t.1.sql offset: 183 error: failed to cast value as varchar(12) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin for column `b` (#2): [types:1406]Data Too Long, field len 12, data len 13 row_data: (77,'seventy-seven') *************************** 3. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.629929 table_name: `example`.`t` path: example.t.1.sql offset: 253 error: failed to cast value as tinyint(4) for column `a` (#1): [types:1690]constant 600 overflows tinyint row_data: (600,'six hundred')
  7. Check whether the conflict_error_v1 table has caught the four rows that have unique/primary key conflicts:

    $ mysql -u root -h 127.0.0.1 -P 4000 -e 'select * from lightning_task_info.conflict_error_v1;' --binary-as-hex -E *************************** 1. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.669601 table_name: `example`.`t` index_name: PRIMARY key_data: 40 row_data: (40, "forty") raw_key: 0x7480000000000000C15F728000000000000028 raw_value: 0x800001000000020500666F727479 raw_handle: 0x7480000000000000C15F728000000000000028 raw_row: 0x800001000000020500666F727479 *************************** 2. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.674798 table_name: `example`.`t` index_name: PRIMARY key_data: 40 row_data: (40, "forty") raw_key: 0x7480000000000000C15F728000000000000028 raw_value: 0x800001000000020600666F75727479 raw_handle: 0x7480000000000000C15F728000000000000028 raw_row: 0x800001000000020600666F75727479 *************************** 3. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.680332 table_name: `example`.`t` index_name: b key_data: 54 row_data: (54, "fifty-four") raw_key: 0x7480000000000000C15F6980000000000000010166696674792D666FFF7572000000000000F9 raw_value: 0x0000000000000036 raw_handle: 0x7480000000000000C15F728000000000000036 raw_row: 0x800001000000020A0066696674792D666F7572 *************************** 4. row *************************** task_id: 1635888701843303564 create_time: 2021-11-02 21:31:42.681073 table_name: `example`.`t` index_name: b key_data: 42 row_data: (42, "fifty-four") raw_key: 0x7480000000000000C15F6980000000000000010166696674792D666FFF7572000000000000F9 raw_value: 0x000000000000002A raw_handle: 0x7480000000000000C15F72800000000000002A raw_row: 0x800001000000020A0066696674792D666F7572

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