| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | bossartn(at)amazon(dot)com, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, michael(at)paquier(dot)xyz, sulamul(at)gmail(dot)com, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: inefficient loop in StandbyReleaseLockList() |
| Date: | 2021-11-06 22:46:48 |
| Message-ID: | 20211106224648.wcmavq6ngv43ysb7@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
On 2021-11-06 18:32:54 -0400, Tom Lane wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2021-11-06 14:06:12 -0400, Tom Lane wrote:
> >> + * Note that this takes time proportional to the length of the list,
> >> + * since the remaining entries must be moved.
> >> */
> >> List *
> >> list_delete_first(List *list)
>
> > Perhaps we could point to list_delete_last()? But it's an improvement without
> > that too.
>
> Good point. The note at list_delete_last that it's O(1) isn't really
> on point --- instead, the text for list_delete_first should be like
>
> + * Note that this takes time proportional to the length of the list,
> + * since the remaining entries must be moved. Consider reversing the
> + * list order so that you can use list_delete_last() instead. However,
> + * if that causes you to replace lappend() with lcons(), you haven't
> + * improved matters.
LGTM
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