[Config] Document 'memtx' configuration settings

[andreyaksenov]

Product: Tarantool
Since: 3.0
Root document:

• A new In-memory storage topic in the Configuration section.
• A new memtx section in the Configuration reference.

SME: @ Totktonada
Child issue: #3509

Details

Options:

• https://github.com/tarantool/tarantool/blob/f58bfc97c627f1838696697339fb3e443c05767a/src/box/lua/config/instance_config.lua#L1124

Related topics:

• https://www.tarantool.io/en/doc/latest/concepts/engines/memtx/
• https://www.tarantool.io/en/doc/latest/reference/configuration/#configuring-the-storage

Related API for administration:

• https://www.tarantool.io/en/doc/latest/release/3.0.0/#database-statistics (not documented yet)
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_space/bsize/
• https://www.tarantool.io/en/doc/latest/reference/reference_lua/box_slab/

Related issues:

• new box.cfg parameter memtx_sort_threads #3509

% tarantool --help-env-list | grep MEMTX
| TT_MEMTX_ALLOCATOR                          | string         | small                                         | Community Edition  |
| TT_MEMTX_MAX_TUPLE_SIZE                     | integer        | 1048576                                       | Community Edition  |
| TT_MEMTX_MEMORY                             | integer        | 268435456                                     | Community Edition  |
| TT_MEMTX_MIN_TUPLE_SIZE                     | integer        | 16                                            | Community Edition  |
| TT_MEMTX_SLAB_ALLOC_FACTOR                  | number         | 1.05                                          | Community Edition  |
| TT_MEMTX_SLAB_ALLOC_GRANULARITY             | integer        | 8                                             | Community Edition  |
| TT_MEMTX_SORT_THREADS                       | integer        | box.NULL                                      | Community Edition  |

[andreyaksenov]

In a new topic, we can also add a link to sizing_calculator:
https://www.tarantool.io/en/sizing_calculator/

We can also mention that estimating the size of RAM depends on whether or not sharding is used.

Some low-level details: https://github.com/tarantool/tarantool/wiki/Memory-size-calculation