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List:       openldap-devel
Subject:    Fwd: Question regarding MDB_NOLOCK
From:       David Barbour <dmbarbour () gmail ! com>
Date:       2015-01-31 7:01:44
Message-ID: CAAOQMSv2J=3=UNVwUSn0yt-iX5oE7z-zE88qamow4jwQf0Ghxw () mail ! gmail ! com
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On Sat, Jan 31, 2015 at 12:54 AM, Howard Chu <hyc@symas.com> wrote:

>
>  My earlier assumption (before reading mdb_page_alloc) was that LMDB
>> would be aggressive about grabbing pages freed by transactions that are
>> not actively being read. If we're relying on `last < oldest` to create a
>> two page discrepancy, this means when we actually have readers on older
>> transactions that we're being little more conservative than necessary.
>>
>
> More than necessary? I don't think so.


You'll conserve exactly one more transaction's free pages than necessary in
the case where a reader-lock exists on any transaction older than the most
recent snapshot.

[Attachment #3 (text/html)]

<div dir="ltr"><div class="gmail_quote"><div dir="ltr"><div class="gmail_extra"><div \
class="gmail_quote"><span class="">On Sat, Jan 31, 2015 at 12:54 AM, Howard Chu <span \
dir="ltr">&lt;<a href="mailto:hyc@symas.com" \
target="_blank">hyc@symas.com</a>&gt;</span> wrote:<br><blockquote \
class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><span><br>
 <blockquote class="gmail_quote" style="margin:0px 0px 0px \
0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
 My earlier assumption (before reading mdb_page_alloc) was that LMDB<br>
would be aggressive about grabbing pages freed by transactions that are<br>
not actively being read. If we&#39;re relying on `last &lt; oldest` to create a<br>
two page discrepancy, this means when we actually have readers on older<br>
transactions that we&#39;re being little more conservative than necessary.<br>
</blockquote>
<br></span>
More than necessary? I don&#39;t think \
so.</blockquote><div><br></div></span><div>You&#39;ll conserve exactly one more \
transaction&#39;s free pages than necessary in the case where a reader-lock exists on \
any transaction older than the most recent \
snapshot.<br></div><div><br></div></div></div></div> </div><br></div>



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