Putting the sessions that aren't doing the update on hold makes the new
mechanism work the same way the old one did with the exception that it
won't put any extra work on the database itself.
As there are no practical benefits to multiple sessions for the same user
mapping the databases at the same time, limiting them to one update per
user is sensible. This is especially true now that we know the
information_schema tables aren't the most efficient things in the world.
The current code implements this rate limiting by closing any extra
sessions that would start a second update. The final implementation should
suspend them for the duration of the update as it is far more
user-friendly.
The limits are currently global as the shard caches are also global. This
is a performance bottleneck and it could be solved by storing the shard
cache inside of a mxs::WorkerGlobal instead of having it as a global
cache.
This allows the set of servers used by the service to also participate in
the cache value resolution. This will prevent the most obvious of problems
but any abstractions of the servers will prevent this from working.
The code only handled the basic version of the command, returning incorrect
results if modifiers were used. The code is now removed, causing the command
to be routed to the backend of the current database. This will give correct
results as long as that backend contains all the tables of the database e.g.
no table sharding.
See script directory for method. The script to run in the top level
MaxScale directory is called maxscale-uncrustify.sh, which uses
another script, list-src, from the same directory (so you need to set
your PATH). The uncrustify version was 0.66.
Changes with ResultSet caused the send_databases and send_tables
functions to always return false. Also changed send_database to
return void since it shouldn't be able to fail anymore.
get_shard_target had become little bloated with the recent changes so
some routing cases were moved to their own functions. Also removed
some code that was not needed.
Add support for binary protocol prepared statements for schemarouter.
This implementation doesn't yet attempt to handle all the edge cases.
Prepared statements are routed to the server that contains the affected
tables, the internal id from the server is then mapped to the session
command id that is inceremented for each prepared statement. This unique
session command id is returned to the client because internal id given
by server might be same around different servers and this way it is
possible to keep track of them and route them to the right servers when
executed.
The schemarouter now also uses versioned configurations implemented by
shared pointers to configuration objects. Moved all the configuration
management into the Config class. Removed router options from
schemarouter.
Previously schemarouter only mapped databases to the servers
they were resided on. Now all the tables are also mapped to allow the
router to route queries to the right server based on the tables used in
that query.
Using the same implementation of the Backend and SessionCommand classes in
both schemarouter and readwritesplit will prevent duplication of code.
This commit only splits the generic parts of the class to a Backend class
which the schemarouter then extends. The session commands for both routers
are similar so they require no special handling.
