[tarantool-patches] Re: [PATCH 0/8] rfc: introduce dry-run execution of SQL queries

[Konstantin Osipov]

* Nikita Pettik <korablev at tarantool.org> [19/08/27 16:34]:
> To execute query in dry-run mode locally separate method of box has been added:
> box.dry_run("sql_string"). Current implementation does not modify box.execute()
> making it accept third optional argument (except for array of bindings) - this
> is to be discussed. 

If you have to use a separate method, call it "prepare", and
return a prepare handle. The handle may simply contain SQL text as
prepared state, + metadata. Let's not invent a new API, dry run is
an implementation detail.

> Other open (or dubious) questions.
> 
> 1. How to handle DML queries. Meanwhile getting meta-information of DDL queries
> is likely to be useless, calculating number of affected rows in case of DML
> query can be sensible. On the other hand, it can turn out to be quite
> non-trivial task.  In its current state, box.dry_run("DML_Query") always
> returns 0 as row count. IMHO it can be done but as a follow-up

The point of dry-run in particular is to find out on the driver
side whether the query returns a result set or not. So please
handle them.

> 2. Should dry_run() except for parsing also bind variables? I guess no, since
> it results in byte-code (i.e. prepared statement) modification. On the other
> hand, it allows setting correct type for bindings (see sql_bind_type()). By
> default, all binding parameters have boolean type.

No, dry-run is an alias to 'prepare', which doesn't return a
prepare handle only because we decided to use SQL text as a
prepared statement identifier, and hide an explicit prepared
statement handle from the client. The prepared statement cache
will be managed transparently by the server when it is added, for
two reasons:

- to not force this complication on the client
- to be able to use prepared statements with statements which were
  not explicitly prepared.

An important detail: for this reason, dry run should also return
the number of parameter markers, their type and count.


> 3. Interface for local call. In current implementation I've added box.dry_run()
> in addition to traditional box.execute() method. Instead, we can make
> box.execute() accept third argument as it is handled in net.box.

Replied.

I will look at the patch separately.


-- 
Konstantin Osipov, Moscow, Russia