Entries in -w (2)

Why doesn’t my query 'select from reallybigtable' ever return?

It's a valid query, but q will run out of memory before returning. You'll have to add some constraints to the query to reduce the size of the result set. Something like

select from reallybigtable where date = YYYY.MM.DD

would be a good start.

How do i interpret the output of function .Q.w[]?

An example explains it best:

$ rlwrap q
KDB+ 2.7 2011.02.16 Copyright © 1993-2011 Kx Systems
q).Q.w[]
used| 108432   / bytes malloced
heap| 67108864 / heap bytes available
peak| 67108864 / heap high-watermark in bytes
wmax| 0        / workspace limit from -w param
mmap| 0        / amount of memory mapped
syms| 537      / number of symbols interned
symw| 15616    / bytes used by 537 symbols
q)

Note how .Q.w is simply a pretty print output of \w and the workspace memory footprint from \w 0

q).Q.w
k){`used`heap`peak`wmax`mmap`syms`symw!(."\\w"),."\\w 0"}
q)\w
108304 67108864 67108864 0 0j
q)