vanishing history

vanishing history

[Adam Spiers]

Does anyone have any idea why my .zshhistory occasionally looses the
vast majority of its contents?  I can't reproduce it, so I can't begin
to track down what's going on.  I have the following settings:

HISTSIZE=3000
cshjunkiehistory
extendedhistory
histallowclobber
histexpiredupsfirst
histignorealldups
histignoredups
histreduceblanks
histverify
incappendhistory

I'm running 4.1.0-dev-2 from CVS.  I have a _very_ vague suspicion
that it might be something to do with running different versions of
zsh on the same history file, or maybe zcompile comes into it somehow,
but really I haven't a clue.  I wanted to get my .zshrc to
automatically alert me when it happens, via:

  _check_hist_size () {
    fc_out=( $(fc -l -1) )
    if (( "$fc_out[1]" < 500 )); then
      print "\nWARNING: Small history ($fc_out[1]) detected\!"
    fi
  }

but that just resulted in:

  _check_hist_size:fc:1: no such event: 0
  _check_hist_size:2: no such file or directory: 500

Re: vanishing history

[Wayne Davison]

On Wed, 28 Nov 2001, Adam Spiers wrote:
> Does anyone have any idea why my .zshhistory occasionally looses the
> vast majority of its contents?  I can't reproduce it, so I can't begin
> to track down what's going on.

I've seen this from time to time, but also have been unable to reproduce
it.  In pouring over the code I did finally see one potential way that
the loss of contents could happen: if the history file is locked by
another process while we're trying to rewrite it.  Here's the fix (which
causes us to just punt on the rewrite if we read nothing):

Index: Src/hist.c
--- Src/hist.c	16 Feb 2002 09:15:07 -0000	1.39
+++ Src/hist.c	16 Feb 2002 09:21:16 -0000
@@ -2083,7 +2083,8 @@
 	    hist_ignore_all_dups |= isset(HISTSAVENODUPS);
 	    readhistfile(fn, err, 0);
 	    hist_ignore_all_dups = isset(HISTIGNOREALLDUPS);
-	    savehistfile(fn, err, 0);
+	    if (histlinect)
+		savehistfile(fn, err, 0);
 	    deletehashtable(histtab);

 	    curhist = remember_curhist;

..wayne..