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From: Bart Schaefer <schaefer@brasslantern.com>
Date: Fri, 24 Jun 2016 18:47:47 -0700
Message-ID: <CAH+w=7YQz6iaJf0k=OkX2bQSL26ohU3wLRVYgki_Z6jLOYpzSw@mail.gmail.com>
Subject: Re: Memory usage of history?
To: Zsh Users <zsh-users@zsh.org>, Robin Dapp <rdapp@linux.vnet.ibm.com>
Content-Type: text/plain; charset=UTF-8

On Fri, Jun 24, 2016 at 6:47 AM, Dominik Vogt <vogt@linux.vnet.ibm.com> wrote:
>
> (A colleague
> says his zshs use 200 MB memory each with a history size of a
> million lines).

To expand on Eric's answer, zsh reads the entire $HISTFILE and retains
the last $HISTSIZE entries.  So a large $HISTFILE also slows down
startup, even if it doesn't consume lots of memory.

I can't imagine anyone having a million useful lines of history.  A
few tens of thousands at most.  Things he might consider that would
allow him to reduce SAVEHIST and/or HISTSIZE without losing too much
information:
* Set the hist_ignore_all_dups option, if he doesn't already.
* Set the hist_save_no_dups option, similarly.
* Define a zshaddhistory function to filter out commands that are
unlikely to be used again.

If he isn't already ignoring / not saving duplicates, an interesting
experiment might be to add hist_ignore_all_dups without changing
HISTSIZE, then run zsh and see how many lines of history actually end
up being retained.