The Write Ahead Log (WAL) is one of the most important components of a database. All the changes to data files are logged in the WAL (called the redo log in InnoDB). This allows to postpone the moment when the modified pages are flushed to disk, still protecting from data losses.
The write intense workloads had performance limited by synchronization in which many user threads were involved, when writing to the redo log. This was especially visible when testing performance on servers with multiple CPU cores and fast storage devices, such as modern SSD disks.
We needed a new design that would address the problems faced by our customers and users today and also in the future. Tweaking the old design to achieve scalability was not an option any more. The new design also had to be flexible, so that we can extend it to do sharding and parallel writes in the
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