sql: expose KV range metadata to SQL for "experienced" admins

[knz]

This is a follow-up to #8938, a proposal to implement two new functions:

• crdb_encode_pkey(table_or_index_name, expr...), returning bytea, with table_or_index_name a string or identifier (string would be more easy and would create an opportunity to play with the virtual schema). This would compute and return the KV-level key encoding for the primary key of the specified table/index using the values given in the other arguments.
• crdb_current_range_bounds(pkey), where pkey is a bytea, returning a tuple of two bytea, with the two values are the current known range bounds for the range containing pkey.

The two functions in combinations can then be used to estimate "distance" between two rows in a table, in the sense of whether they belong to the same range or not, and can be used as a follow-up to #8938 to check that a split requested with "ALTER TABLE ... SPLIT" was actually processed.

The function names are just proposals.

cc @mjibson

[knz]

Once this is available the SPLIT AT syntax can be simplified to take a simple bytea expression that is the result of the encode_pkey function.

[a6802739]

@knz, please give me some more reference and I have time to fix it now.

[knz]

@a6802739 Please review #8938 and the discussion that accompanied the PR to see if you understand what this feature is about. Then we can discuss if you have questions.

[a6802739]

@knz , I start to fix this issue.

about crdb_encode_pkey(table_or_index_name, expr...), do you mean wee add this function to encode primary key value to kv value which is used in kv level. it should be like /Table/TableID/PrimaryID/Value, so how can we map the table name or the index name to the specified id?

about crdb_current_range_bounds(pkey), do you mean to find the correct range contains the key?it seems in testutils/serverutils/test_server_shim.go , it already has function LookupRange.

[knz]

For the first point you need to investigate the table/index descriptors.

For the second point yes the solution will need LookupRange.

[petermattis]

@knz Now that we have SHOW TESTING_RANGES, is there anything left to do here?

[knz]

No indeed