.Q.qp for splayed table

Community Support
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1

https://learninghub.kx.com/forums/topic/q-qp-for-splayed-table

The .Q.qp doc says 0b for splayed table, but on KDB 4.0 it’s actually 0. Is it a bug, or there is a new way to check if a table is splayed?

 

q)`:./t/ set ([] v1:10 20 30; v2:1.1 2.2 3.3) 
`:./t/ 

q)l ./t 
`t 

q)0b~.Q.qp t x
0b 

q)0~.Q.qp t 
1b

 

 

2

If you refer here: https://code.kx.com/q/basics/syscmds/#l-load-file-or-directory

  • serialized object, deserializes it into memory as variable name
  • directory of a splayed table, maps the table to variable name, without loading any columns into memory
When you are running, l .t -> you are loading the object as t in root. Thus .Q.qp is showing t as 0

% ls -lrth t
total 16
-rw-r–r– 1 sujoyrakbleep staff 40B Sep 17 17:20 v1
-rw-r–r– 1 sujoyrakbleep staff 40B Sep 17 17:20 v2

% q
KDB+ 4.0 2021.07.12 Copyright (C) 1993-2021 Kx Systems
q)l .
q)a
,t q).Q.qp t 0b q)l t t
q).Q.qp t
0

 

3

Thanks @sujoy13. What confused me is “directory of a splayed table”, which I interpreted as directory t as in your example.

A follow-up question: what is the real runtime difference between l . and l t for this particular example? The latter form also maps the table without copying data from disk to memory. By the way t is layed out on the disk, it is a splayed table…