Re: HISTSIZE

[Zoltan Hidvegi <hzoli@cs.elte.hu>]

> I have noticed that when I set HISTSIZE (the maximum size of the
> history list) in zsh to something huge, zsh takes huge amounts of
> memory.
> 
> When I converted from bash, I have easily ported all the init files,
> and HISTSIZE caused terrible problems (especially since I didn't know
> HISTSIZE was causing them). The reason I set HISTSIZE to such a big
> value is just to keep it from bothering me -- it is just a *maximum*
> value I am changing. In bash it worked exactly that way (no additional
> memory expense). But it seems that the organization of history storage
> requires resizehistevents() to reallocate the list to HISTSIZE history
> entries.
> 
> I wonder how difficult would it be to patch hist.c in such a way that
> the actual size of the history list changes dynamically, HISTSIZE
> being only an upper limit to that change.

Zsh uses a HISTSIZE long array to store history entries.  gethistent(X) is
defined as (histentarr+((X)%histentct)) (with proper bounds checking at
apropriate places).  This is usually the most compact representation.  A
linked list can be used but then the pointers would require extra memory.
histentarr is almost full in most cases since it is filled from $HISTFILE
upon invocation.  Most people do like to limit the number of stored history
events since loading and saving big histories takes a long time.  Of course
SAVEHIST can be smaller than HISTSIZE but most people do not issue more
than 1000 commands from one shell so HISTSIZE = SAVEHIST + 1000 should be
enough.

Zoltan