[tarantool-patches] Re: [PATCH] Do not update schema_version on space:truncate().

[Sergey Petrenko <sergepetrenko@tarantool.org>]

06.07.2018 17:07, Konstantin Osipov пишет:
> * Serge Petrenko <sergepetrenko@tarantool.org> [18/07/06 14:52]:
>> Schema version is used by both clients and internal modules to check
>> whether there vere any updates in spaces and indices. While clients
>> only need to be notified when there is a noticeable change, e.g.
>> space is removed, internal components also need to be notified when
>> something like space:truncate() happens, because even though this
>> operation doesn't change space id or any of its indices, it creates a
>> new space object, so all the pointers to the old object have to be updated.
>> Currently both clients and internals share the same schema version, which
>> leads to unnecessary updates on the client side.
>>
>> Fix this by implementing 2 separate counters for internal and public use:
>> schema_state gets updated on every change, including recreation of the same
>> space object, while schema_version is updated only when there are noticable
>> changes for the clients. Introduce a new AlterOp to alter.cc to update
>> public schema_version.
>> Now all the internals reference schema_state, while all the clients use
>> schema_version. box.iternal.schema_version() returns schema_version
>> (the public one).
> The new schema is instantiated/becomes effective in do(), not in commit.
>
> Before do() and commit() there is a yield and new queries
> can see the new schema already.
>
Will fix. I thought it'd be a good idea to only increment when we 
already know
we won't be returning to the old state.
So I should increase schema_version in UpdateSchemaVersion::alter() and 
decrease it in
UpdateSchemaVersion::rollback() ? And what about creation/drop of a 
space? Move
schema_version increment to on_replace_dd_space() and decrement in case 
of failure to
on_create_space_rollback() / on_drop_space_rollback() ?