[RFC CQL v4+] cql_extension: wide range of unset values.

 
Problem

The current implementation of unset_value regularly fails (see Issues).
We need to implement a new unset_value(s) mechanism which is robust and will work well for v4+ protocols.

Issues

1- A client has to encode unset_value for all the columns
in an insert-prepared query values.

example: INSERT INTO table(pkey,ckey,col1,col2,col3,col4) values(?,?,?,?,?,?);

An execute query should unset all the columns one by one by encoding unset_value as "int(-2)"

a- binded-values = (pkey_value, ckey_value, col1_value, unset_value, unset_value, unset_value) or
b- binded-values = (pkey_value, ckey_value, unset_value, unset_value, unset_value, col4_value) etc.

this increase the execute query binary buffer which is in term increase the bandwidth and latency for both request/response.

2- Returning Select-queries buffer not differentiate between null and unset_value for a subset of given rows.

example:
imagine you have a dataset in the table where each row of the returning select response have different
unset/null columns, consider the following query:
SELECT * FROM table where pkey = pkey_value;
and with a page_size = 3 rows ,

 

 

Proposed solution

Instead of just having null(-1) and unset_value(-2), extending the unset_value(s)
to a range from unset_(-2) to unset_(-2,147,483,648),
where unset_value = unset_(-2)
unset_rest = unset_(-2,147,483,648)
anything in between will be unset_(neg_integer).

Solution for issue_1:

a- binded-values = (pkey_value, ckey_value, col1_value, unset_rest)
b- binded-values = (pkey_value, ckey_value, unset_(-4), col4_value)

Solution for issue_2:

work with all select-un/prepared responses.

row1 buffer -> pkey_value, ckey_value, col1_value, unset_rest.
this will enable the buffer to shift to a new row.

row2 buffer -> pkey_value, ckey_value, unset_(-4), col4_value.
this will enable the buffer to skip the columns metadata -4+1=-3 columns and start decoding from col4 for the next cell_value in the row.

row3 buffer -> pkey_value, ckey_value, unset_(-3), col3_value, unset_rest.
this buffer is a mix of row1/row2.

this solution not limited to unset_(neg-int) , it can be used on null cell responses to decrease the bandwidth between CQL and client.

to be compatible with all the current v4+ cql/drivers, we should force the client to send a flag with the select query request (either in the frame-header or somewhere in the cql statement),
and for returning buffer we could use the rows flags (ex, has_unset_values?: boolean) to let the driver know if it exist in the page.

Benefits

-implementing this will enable apps to design complex data-model up to 2 billion columns without trading off anything.

-reducing the number of write-prepared statements in datamodel with millions of columns to a highest degree.

-huge impact on the bandwidth/cpu-cycles.
 
-easy to implement in the client side.

Record of votes

+1 Louay Kamel