PARTITION BY KEY ALGORITHM={crc32|murmur|...}

As of 10.5, MariaDB supports 1 and 2 in the ALGORITHM option of a PARTITION clause:

CREATE TABLE t1 (a VARCHAR(64)) PARTITION BY KEY ALGORITHM=1 (a) PARTITIONS 4;

CREATE TABLE t1 (a VARCHAR(64)) PARTITION BY KEY ALGORITHM=2 (a) PARTITIONS 4;

where:

• 1 means MySQL 5.1 hash
• 2 means MySQL 5.5 hash

The built-in hash functions are not always good. For example, on BINARY-alike or VARBINARY-alike data types the distribution is not good when the data has many zero bytes.

See MDEV-20791 as an example of a bad distribution.

In order to improve distribution, let's implement more hash options, e.g. crc32, murmur:

CREATE TABLE t1 (a VARCHAR(64)) PARTITION BY KEY ALGORITHM=crc32 (a) PARTITIONS 4;

CREATE TABLE t1 (a VARCHAR(64)) PARTITION BY KEY ALGORITHM=murmur (a) PARTITIONS 4;

New algorithm options will be identified by textual names instead of numbers. As this is more readable.

The old values of 1 and 2 will remain as numbers (for backward compatibility). Optionally, they can get textual aliases, e.g. mysql51 or mysql55:

ALGORITH=mysql51