Re: [tarantool-patches] [PATCH] box: add on_schema_init trigger

[Vladimir Davydov <vdavydov.dev@gmail.com>]

On Tue, Mar 05, 2019 at 10:54:54AM +0300, Konstantin Osipov wrote:
> * Serge Petrenko <sergepetrenko@tarantool.org> [19/03/03 23:25]:
> > This patch introduces an on_schema_init trigger. The trigger may be set
> > before box.cfg() is called and is called during box.cfg() right after
> > prototypes of system spaces, such as _space, are created. This allows to
> > set triggers on system spaces before any other non-system data is
> > recovered. For example, it is possible to set an on_replace trigger on
> > _space, which will work even during recovery.
> > 
> > Part of #3159
> > 
> > @TarantoolBot document
> > Title: document box.ctl.on_schema_init triggers
> > on_schema_init triggers are set before the first call to box.cfg() and
> > are fired during box.cfg() before user data recovery start.
> 
> Please explain in the docbot request why we're adding this with
> an example: provide the docs team with a full example how to use
> these triggers to easily change space engine type in replication events
> or make a space on a replicate "terminate" in replication by
> changing its group id to GROUP_LOCAL.
> 
> > 
> > diff --git a/src/box/lua/ctl.c b/src/box/lua/ctl.c
> > index 7010be138..0767cf476 100644
> > --- a/src/box/lua/ctl.c
> > +++ b/src/box/lua/ctl.c
> > @@ -40,6 +40,7 @@
> >  #include "lua/trigger.h"
> >  
> >  #include "box/box.h"
> > +#include "box/schema.h"	/* on_schema_init triggers */
> 
> 
> Please move the declaration to a more suitable place (box/box.h?)
> to avoid polluting the include list.

IMO having on_schema_init defined in schema.cc (we can't move it to
box.cc) and declared in box.h would look confusing.

> 
> > +trig = box.ctl.on_schema_init(testing_trig)
> > +test:is(type(trig), 'function', 'on_schema_init trigger set')
> > +
> > +box.cfg{log = 'tarantool.log'}
> > +test:like(str, 'on_schema_init', 'on_schema_init trigger works')
> > +str = ''
> > +box.schema.space.create("test")
> > +-- test that _space.on_replace trigger may be set in on_schema_init
> > +test:like(str, '_space:on_replace', 'can set on_replace')
> > +test:check()
> > +box.space.test:drop()
> > +os.exit(0)
> 
> Please write a full test for changed storage engine on replica *in
> addition to* this unit test. Another test for replica-local spaces
> on replica won't hurt.

Nit: I'd also rename the test from box-tap/ctl_on_schema_init.test.lua
to box-tap/on_schema_init.test.lua.