Disable implicit box.cfg{} in sql

[Mons]

In #3266 there were added implicit empty box.cfg{} to box.execute

At first, this behavior differs from other functions like box.select etc.
At second, this could be harmful, because calling empty box.cfg will start an instance without replication in readwrite mode, which, in case, could lead to unintended background data modification

I could not see a reason for implicit cfg inside sql and I insist on strict requirement of explicit box.cfg from box.execute

[Gerold103]

There was a certain reason to add auto box.cfg - interactive SQL console. In the SQL console you can't call box.cfg{}. Its auto call in the console should be preserved.

[kyukhin]

Maybe there's a way to do implicit cfg{} in interactive mode only?

[Gerold103]

There is. Just patch console.lua to call box.cfg in case SQL language is active, and it was not called before a first request.

[Totktonada]

It is possible now using built-in LUA function:

SELECT lua('box.cfg{listen = 3301} return true')

See tarantool/doc#879

[igormunkin]

I found the following example today:

$ ./src/tarantool
Tarantool 2.5.0-98-ge215737a9
type 'help' for interactive help
tarantool> \set language sql
---
- true
...

tarantool> SELECT 1
2020-06-03 23:51:55.373 [20388] main/103/interactive C> Tarantool 2.5.0-98-ge215737a9
2020-06-03 23:51:55.373 [20388] main/103/interactive C> log level 5
2020-06-03 23:51:55.374 [20388] main/103/interactive I> mapping 268435456 bytes for memtx tuple arena...
2020-06-03 23:51:55.374 [20388] main/103/interactive I> mapping 134217728 bytes for vinyl tuple arena...
2020-06-03 23:51:55.380 [20388] main/103/interactive I> instance uuid 8a4ec0ff-590b-4a68-b2b8-4edcfa49d35c
2020-06-03 23:51:55.380 [20388] main/103/interactive I> initializing an empty data directory
2020-06-03 23:51:55.405 [20388] main/103/interactive I> assigned id 1 to replica 8a4ec0ff-590b-4a68-b2b8-4edcfa49d35c
2020-06-03 23:51:55.405 [20388] main/103/interactive I> cluster uuid f7a600e4-4913-43b1-aec4-02ec9e4fb45a
2020-06-03 23:51:55.406 [20388] snapshot/101/main I> saving snapshot `./00000000000000000000.snap.inprogress'
2020-06-03 23:51:55.439 [20388] snapshot/101/main I> done
2020-06-03 23:51:55.440 [20388] main/103/interactive I> ready to accept requests
2020-06-03 23:51:55.440 [20388] main/105/checkpoint_daemon I> scheduled next checkpoint for Thu Jun  4 01:04:01 2020
---
- metadata:
  - name: '1'
    type: integer
  rows:
  - [1]
...

tarantool> SELECT lua('box.cfg{log="tarantool.log"} return true')
---
- null
- Can't set option 'log' dynamically
...

[Totktonada]

@igormunkin log is not a dynamic option.

$ tarantool
Tarantool 2.5.0-62-gbb7c3d167
type 'help' for interactive help
tarantool> box.cfg{}
<...>
tarantool> box.cfg{log = 'log.txt'}
---
- error: Can't set option 'log' dynamically
...

Are you want to highlight that we're unable to tune a non-dynamic option after a box.execute(<...>) call (as well as after box.cfg(<...>) call)?

[igormunkin]

Are you want to highlight that we're unable to tune a non-dynamic option after a box.execute(<...>)call (as well as after box.cfg(<...>) call)?

Precisely.

[Totktonada]

I don't have an opinion regarding which decision would be better here, but I want to note that it may depend on other activities around box.cfg(). Cited from my email re #4231:

Also I'm not sure that disabling implicit box.cfg() is the right
direction. Maybe we should make all box.cfg() options dynamically
configurable, allow to join a cluster with initial snapshot (after very
first box.cfg()), dynamically adjust memtx_memory if it is not set
explicitly and make other improvements for user's convenience.

I have no opinion here, just noted that it is not so clear as it may
look at first glance.