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 how to use the type error feature (lightning.max-error) and the duplicate resolution feature (tikv-importer.duplicate-resolution). It also introduces the database where these errors are stored (lightning.task-info-schema-name). At the end of this document, an example is provided.

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 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.
• Unique/Primary key conflict in TiDB-backend, when on-duplicate = "error".
• Any other SQL errors.

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

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

Unique/Primary key conflict in the Local-backend is handled separately and explained in the next section.

Duplicate resolution in Local-backend mode

In the Local-backend mode, TiDB Lightning imports data by first converting them to KV pairs and ingesting the pairs into TiKV in batches. Unlike the TiDB-backend mode, duplicate rows are not detected until the end of a task. Therefore, duplicate errors in the Local-backend mode are not controlled by max-error, but rather by a separate configuration duplicate-resolution.

[tikv-importer]
duplicate-resolution = 'none'

The value options of duplicate-resolution are as follows:

• 'none': Does not detect duplicate data. If a unique/primary key conflict does exist, the imported table will have inconsistent data and index, and will fail checksum check.
• 'record': Detects duplicate data, but does not attempt to fix it. If a unique/primary key conflict does exist, the imported table will have inconsistent data and index, and will skip checksum and report the count of the conflict errors.
• 'remove': Detects duplicate data, and removes all duplicated rows. The imported table will be consistent, but the involved rows are ignored and have to be added back manually.

TiDB Lightning duplicate resolution can detect duplicate data only within the data source. This feature cannot handle conflict with existing data before running TiDB Lightning.

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 TYPE	ERROR COUNT	ERROR DATA TABLE
  1	Data Type	1000	lightning_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 syntax_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,
    context     text
);

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)
);

type_error_v1 records all type errors managed by the max-error configuration. There is one row per error.

conflict_error_v1 records all unique/primary key conflict in the Local-backend. There are 2 rows per pair of conflicts.

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, 'fourty'),         -- 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, delete 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/'
       duplicate-resolution = 'remove'
   
       [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, "fourty")
       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