What should be done?

Currently, both handler-level and backends-level batch sizes are constants. That's because we don't want to consume too much memory on the FerretDB side and go over backend limits such as a maximum number or size of query parameters. We also don't know how to detect and/or auto-tune those parameters yet.

But we should allow changing those values via testing flags.

Where?

See reference above.

Definition of Done

• handler updated;
• all backends updated;
• benchmarks updated and run;
• spot refactorings done.