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.Q.qp for splayed table
The .Q.qp doc says
0bfor splayed table, but on KDB 4.0 it’s actually0. 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
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2 Replies
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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 sujoyrak**bleep** staff 40B Sep 17 17:20 v1
-rw-r–r– 1 sujoyrak**bleep** 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 - serialized object, deserializes it into memory as variable
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Thanks @sujoy13. What confused me is “directory of a splayed table”, which I interpreted as directory
tas in your example.A follow-up question: what is the real runtime difference between
l .andl tfor this particular example? The latter form also maps the table without copying data from disk to memory. By the waytis layed out on the disk, it is a splayed table…
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