Table Filter

The TiDB migration tools operate on all the databases by default, but oftentimes only a subset is needed. For example, you only want to work with the schemas in the form of foo* and bar* and nothing else.

Since TiDB 4.0, all TiDB migration tools share a common filter syntax to define subsets. This document describes how to use the table filter feature.

Usage

CLI

Table filters can be applied to the tools using multiple -f or --filter command line parameters. Each filter is in the form of db.table, where each part can be a wildcard (further explained in the next section). The following lists the example usage.

• Dumpling:

  ./dumpling -f 'foo*.*' -f 'bar*.*' -P 3306 -o /tmp/data/
  

• TiDB Lightning:

  ./tidb-lightning -f 'foo*.*' -f 'bar*.*' -d /tmp/data/ --backend tidb
  

TOML configuration files

Table filters in TOML files are specified as array of strings. The following lists the example usage.

• TiDB Lightning:

  [mydumper]
  filter = ['foo*.*', 'bar*.*']
  

Syntax

Plain table names

Each table filter rule consists of a "schema pattern" and a "table pattern", separated by a dot (.). Tables whose fully-qualified name matches the rules are accepted.

db1.tbl1
db2.tbl2
db3.tbl3

A plain name must only consist of valid identifier characters, such as:

• digits (0 to 9)
• letters (a to z, A to Z)
• $
• _
• non ASCII characters (U+0080 to U+10FFFF)

All other ASCII characters are reserved. Some punctuations have special meanings, as described in the next section.

Wildcards

Each part of the name can be a wildcard symbol described in fnmatch(3):

• * — matches zero or more characters
• ? — matches one character
• [a-z] — matches one character between "a" and "z" inclusively
• [!a-z] — matches one character except "a" to "z".

db[0-9].tbl[0-9a-f][0-9a-f]
data.*
*.backup_*

"Character" here means a Unicode code point, such as:

• U+00E9 (é) is 1 character.
• U+0065 U+0301 (é) are 2 characters.
• U+1F926 U+1F3FF U+200D U+2640 U+FE0F (🤦🏿‍♀️) are 5 characters.

File import

To import a file as the filter rule, include an @ at the beginning of the rule to specify the file name. The table filter parser treats each line of the imported file as additional filter rules.

For example, if a file config/filter.txt has the following content:

employees.*
*.WorkOrder

the following two invocations are equivalent:

./dumpling -f '@config/filter.txt'
./dumpling -f 'employees.*' -f '*.WorkOrder'

A filter file cannot further import another file.

Comments and blank lines

Inside a filter file, leading and trailing white-spaces of every line are trimmed. Furthermore, blank lines (empty strings) are ignored.

A leading # marks a comment and is ignored. # not at start of line is considered syntax error.

# this line is a comment
db.table   # but this part is not comment and may cause error

Exclusion

An ! at the beginning of the rule means the pattern after it is used to exclude tables from being processed. This effectively turns the filter into a block list.

*.*
#^ note: must add the *.* to include all tables first
!*.Password
!employees.salaries

Escape character

To turn a special character into an identifier character, precede it with a backslash \.

db\.with\.dots.*

For simplicity and future compatibility, the following sequences are prohibited:

• \ at the end of the line after trimming whitespaces (use [ ] to match a literal whitespace at the end).
• \ followed by any ASCII alphanumeric character ([0-9a-zA-Z]). In particular, C-like escape sequences like \0, \r, \n and \t currently are meaningless.

Quoted identifier

Besides \, special characters can also be suppressed by quoting using " or `.

"db.with.dots"."tbl\1"
`db.with.dots`.`tbl\2`

The quotation mark can be included within an identifier by doubling itself.

"foo""bar".`foo``bar`
# equivalent to:
foo\"bar.foo\`bar

Quoted identifiers cannot span multiple lines.

It is invalid to partially quote an identifier:

"this is "invalid*.*

Regular expression

In case very complex rules are needed, each pattern can be written as a regular expression delimited with /:

/^db\d{2,}$/./^tbl\d{2,}$/

These regular expressions use the Go dialect. The pattern is matched if the identifier contains a substring matching the regular expression. For instance, /b/ matches db01.

Multiple rules

When a table name matches none of the rules in the filter list, the default behavior is to ignore such unmatched tables.

To build a block list, an explicit *.* must be used as the first rule, otherwise all tables will be excluded.

# every table will be filtered out
./dumpling -f '!*.Password'

# only the "Password" table is filtered out, the rest are included.
./dumpling -f '*.*' -f '!*.Password'

In a filter list, if a table name matches multiple patterns, the last match decides the outcome. For instance:

# rule 1
employees.*
# rule 2
!*.dep*
# rule 3
*.departments

The filtered outcome is as follows: