Output Files

mydumper generates several files during the generation of the dump. Many of these are for the table data itself since every table has at least one file.

Metadata

When a dump is executed a file called metadata.partial is created in the output directory and is renamed to metadata when mydumper finish without error. This contains the start and end time of the dump as well as the master binary log positions if applicable.

This is an example of the content of this file:

Started dump at: 2011-05-05 13:57:17
SHOW MASTER STATUS:
  Log: linuxjedi-laptop-bin.000001
  Pos: 106

Finished dump at: 2011-05-05 13:57:17

Since version 0.14.1-1 format has been changed to:

# Started dump at: 2023-06-09 11:47:18
[master]
# Channel_Name = '' # It can be use to setup replication FOR CHANNEL
File = mydumper1-bin.000017
Position = 241149225
Executed_Gtid_Set = 7b166a41-65a2-11ed-9de3-0800275ff74d:1-147115,7b166a41-65a2-11ed-9de3-0800275ff74e:1-61558

[`sakila`.`store`]
Rows = 2
data_checksum = 3119812626
schema_checksum = B7B99B4C
indexes_checksum = B4D31E3

[`sakila`]
schema_checksum = FDF2173B
post_checksum = 42085F07
# Finished dump at: 2023-06-09 11:47:18

Table Data

The data from every table is written into a separate file, also if the --rows option is used then each chunk of table will be in a separate file. The file names for this are in the format:

database.table.sql(.gz|.zst)

or if chunked:

database.table.chunk.sql(.gz|.zst)

Where ‘chunk’ is a number padded with up to 5 zeros or:

database.table.chunk.chunk2.sql(.gz|.zst)

Where ‘chunk2’ is a number padded with up to 5 zeros.

Table Schemas

As long as the --no-schemas option is not specified, mydumper will create a file for the schema of every table it is writing data for. The files for this are in the following format:

database.table-schema.sql(.gz|.zst)

Compression (since 0.15.1-1)

By default, mydumper is not compressing backup. In order to compress the file you need to use -c which by default is going to use GZIP compression method. You can also use ZSTD to compress your backups. The internal compression mechanisim has been removed from the code and we are using /usr/bin/gzip and /usr/bin/zstd. If you need to change to a different location or different compression software, you need to set:

--exec-per-thread
--exec-per-thread-extension

For example:

mydumper -o data --clear -T sakila.film --exec-per-thread="/usr/bin/bzip2" --exec-per-thread-extension=".bz2"
-rw-r--r-- 1 circleci circleci   520 Jul 16 13:59 metadata
-rw-r----- 1 circleci circleci 11500 Jul 16 13:59 sakila.film.00000.sql.bz2
-rw-r----- 1 circleci circleci 11360 Jul 16 13:59 sakila.film.00001.sql.bz2
-rw-r----- 1 circleci circleci   758 Jul 16 13:59 sakila.film-schema.sql.bz2
-rw-r----- 1 circleci circleci   322 Jul 16 13:59 sakila-schema-create.sql.bz2
myloader -d data -o --exec-per-thread="/usr/bin/bzip2 -d" --exec-per-thread-extension=".bz2"

Daemon mode

Daemon mode does things a little differently. There are the directories 0 and 1 inside the dump directory. These alternate when dumping so that if mydumper fails for any reason there is still a good snapshot. When a snapshot dump is complete the last_dump symlink is updated to point to that dump.

If binary logging is enabled mydumper will connect as if it is a slave server and constantly retreives the binary logs into the binlogs subdirectory.