skeema / skeema / 10966171821

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docker: disable doublewrite buffer on ephemeral DB instances

This commit improves performance of ephemeral Dockerized database servers
created by Skeema's workspace=docker option, as well as by Skeema's
integration test suites. Newly-created Dockerized instances will now have
the --skip-innodb-doublewrite option applied.

InnoDB's doublewrite buffer is a crash-safety mechanism, which is normally
very important for "real" database servers, but it isn't necessary for
ephemeral DBs which can be easily destroyed and recreated at will.

Disabling the doublewrite buffer seems to improve integration test execution
time by ~5% on MySQL 8.0+, likely because the server's internal data
dictionary is now stored in InnoDB pages instead of frm files. Similar gains
are expected when using workspace=docker with MySQL 8.0+ flavors, although
the impact will be more modest if running on Linux with docker-cleanup=destroy
due to automatic use of tmpfs in that situation (see commit 766efc3).

The improvement may be negligible on MySQL 5.x or any version of MariaDB,
since these flavors still use frm files. However, for uniformity it is enabled
on all new containers created by workspace=docker or integration tests.

This setting is only applied to newly-created Docker containers. If you have
existing Skeema-managed containers (either from workspace=docker without
docker-cleanup=destroy, or from Skeema integration tests), you must manually
remove them first if you wish for Skeema to recreate them with the new
setting applied.

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