SAMU-64 Allow administrators to enable or disable parallel replication on a per-table basis

Per-domain dedicated thread for processing ordered transactions. The

thread is reserved from the total number of domain threads (controlled

by slave_parallel_threads and slave_domain_parallel_threads). Whether

the event goes to ordered thread depends on FL_ALLOW_PARALLEL flag as

well as several other conditions. FL_ALLOW_PARALLEL is passed from

master and is set for the event depending on master configuration

directives. To allow dedicated slave on server one must enable it

explicitly with configuration directive:

  set global slave_ordered_thread= 1;

Originally it was controlled by skip_parallel_replication session

variable which can be changed per-statement. This patch adds several

more directives to control it on per-schema and per-table levels:

  parallel_do_db

  parallel_do_table

  parallel_ignore_db

  parallel_ignore_table

  parallel_wild_do_table

  parallel_wild_ignore_table

Each directive is comma-separated list of fully-qualified table

names. Spaces after comma are ignored (but not before).

"Table" directives take precedence over "db" directives. "Do"

directives take precedence over "ignore" directives. "Wild" directives

are checked if "do" and "ignore" directives did not match.

If none of the above directives present everything is considered

parallel. If any of the above directives present and the table did not

match anything in the lists it is considered ordered.

Examples:

  set @@global.parallel_do_db=	   "db_parallel";

  set @@global.parallel_ignore_db= "db_serial";

  set global parallel_do_table=  "db_serial.t3,  db_serial.t1";

  set global parallel_wild_ignore_table= "db_parallel.non_parallel_%"

Normal behaviour of ordered transaction is before start to wait any of

prior transactions to commit: they get into different commit

groups. But since all the ordered transactions (within one domain) go

to a single thread we may avoid that restriction with this directive

on slave:

  set global slave_ordered_dont_wait= 1;

When set events without explicit FL_WAITED flag going to ordered

thread nonetheless accept optimistic speculation. I.e. they get into

same commit group with parallel events: ordered event is executed in

parallel with parallel events.