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MySQL 8.0.20 new features | MySQL 8.0.20 enhancements

MySQL 8.0.20 InnoDB enhancement:
Improvement for CATS:
CATS - Contention Aware Transaction Scheduling is improved in MySQL 8.0.20. For CATS transaction weight computation is required. From MySQL 8.0.20 this CATS weight computation is performed on separate thread entirely, which improves performance computation performance and accuracy. FIFO (First in first out) is removed from MySQL 8.0.20. Transaction scheduling performed by the CATS algorithm since MySQL 8.0.20, which used be performed by FIFO.
Explore more:
https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-20.html
https://mysqlserverteam.com/contention-aware-transaction-scheduling-arriving-in-innodb-to-boost-performance/
Storage area for Doublewritter:
Doublewritter buffer used to store data in system tablespace, now it is has its own storage area in doublewriter files, which has resulted in flexibility to place double writer buffer pages, increase throughput, reduce write latency. System variable for doublewritter storage are innodb_doublewrite_dir, innodb_doublewrite_files, innodb_doublewrite_pages,
innodb_doublewrite_batch_size.
Binary Log Compression:
MySQL 8.0.20 supports compression of Binary Logs. By default it is OFF. You can enable binary log compression by system variable binlog_transaction_compression. Algorithm zstd is used to compress binary logs. You can set the compression level (1 to 22) by using system variable binlog_transaction_compression_level_zstd. Transaction payloads remain in compressed state on originator, sent to replication slave, replication stream and relay log. Binary log compression saves disk space on originator, and recipient, as well as network bandwidth also. 

Primary Key Check:
System variable sql_require_primary_key was introduced in 8.0.13. MySQL 8.0.20 supports REQUIRE_TABLE_PRIMARY_KEY_CHECK for CHANGE MASTER TO statement. System variable sql_require_primary_key is used to evaluate the primary key check.
REQUIRE_TABLE_PRIMARY_KEY_CHECK, enables a replication slave to select its own policy for primary key checks. When it is ON for replication channel, it sets sql_require_primary_key=ON, when REQUIRE_TABLE_PRIMARY_KEY_CHECK is set to OFF, the sql_require_primary_key system variable value will be OFF. So slave can have its own policy to check primary key. The REQUIRE_TABLE_PRIMARY_KEY_CHECK default value is STREAM, in this situation slave value is replicated from the master for each transaction. Primary key check might help to identify Error: 1032, slave remain behind master in case of batch job for table with millions of rows.
Ref.:
https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-20.html
Explore InnoDB related bugs are fixed in MySQL 8.0.20 at - https://dev.mysql.com/doc/relnotes/mysql/8.0/en/news-8-0-20.html

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