From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21072 invoked by alias); 23 Mar 2017 16:45:11 -0000 Mailing-List: contact zsh-workers-help@zsh.org; run by ezmlm Precedence: bulk X-No-Archive: yes List-Id: Zsh Workers List List-Post: List-Help: X-Seq: 40889 Received: (qmail 23059 invoked from network); 23 Mar 2017 16:45:11 -0000 X-Qmail-Scanner-Diagnostics: from mail-vk0-f45.google.com by f.primenet.com.au (envelope-from , uid 7791) with qmail-scanner-2.11 (clamdscan: 0.99.2/21882. spamassassin: 3.4.1. Clear:RC:0(209.85.213.45):SA:0(-0.0/5.0):. Processed in 0.882098 secs); 23 Mar 2017 16:45:11 -0000 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on f.primenet.com.au X-Spam-Level: X-Spam-Status: No, score=-0.0 required=5.0 tests=RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL,SPF_PASS,T_DKIM_INVALID autolearn=unavailable autolearn_force=no version=3.4.1 X-Envelope-From: schaefer@brasslantern.com X-Qmail-Scanner-Mime-Attachments: | X-Qmail-Scanner-Zip-Files: | Received-SPF: pass (ns1.primenet.com.au: SPF record at _netblocks.google.com designates 209.85.213.45 as permitted sender) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=brasslantern-com.20150623.gappssmtp.com; s=20150623; h=from:message-id:date:in-reply-to:comments:references:to:subject :mime-version; bh=Br44/VTY6c5qmLN2MhQA5Y7upjX7dlvFe/Hn3wUTPTo=; b=0XrUf+bUHnBmzM1W+jxHCpfSmU0cDfp7WHEG/1wRfRa3YH1IIKVWG/tg8gitYOjom/ GVeubV2zsyyVCqm7LqrfRNkx+rg508AZa/Y2C+gAL9302V+N7y7JkbtzG0ARw7oW6uLS +fZ/D1X67HRK1+Q7HxQ1rNWDKM1mpLvVpgpz7emlp6/70SqCKirmAHQvljgUFyn9Fan4 Fc/dpNIHumneUOe2kdYB3foIkROyjT12IebEPYi6zGeQ8ilG936Aac6VWoxyQYn3C7oN mQmiOPI26DIgbpsol1ZmAOji6hLIFss5crcwqJa8wIJI28EXPLgiCWcpwo+3o8gyafq6 QMwQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:message-id:date:in-reply-to:comments :references:to:subject:mime-version; bh=Br44/VTY6c5qmLN2MhQA5Y7upjX7dlvFe/Hn3wUTPTo=; b=CtP17pE2lPKjOdbT6EchMOiQpBjC/JzXNJ8lH+wEbwA2PK2k+O/KGT8MsRdc//M0mF B5APfGnWmy3DGvc50Y42VIGNEkqcXd9627Mi1VuNKN8qfWCIq06FbHsJoKABbKprjcWA 0cCYaGZsmIXwdnTZ2gY0oprJv0kpuLRzZT3Imjqwzy6i+lIdTyAe0HxqVv1hU+UqA3zn t+wjf0owa4BXqGHe/wtqGNXGIccysKcr1cCS/p1wZ07y12sU6PRjznWCQPrmPslni9Js IJzHpztCtOKcfmskXKtdfFhY1+RRLp8qKLHRpjyQhaHzHDRpqGhLpIuNpNBPtjFebEpL pdgw== X-Gm-Message-State: AFeK/H2sP/zMMh52oingn2V8WRnDTPjVoYEks8kKh8v6mraTkJe1IPDzpOd3lnPjIlMGkw== X-Received: by 10.31.234.3 with SMTP id i3mr1630760vkh.36.1490287504296; Thu, 23 Mar 2017 09:45:04 -0700 (PDT) From: Bart Schaefer Message-Id: <170323094602.ZM8458@torch.brasslantern.com> Date: Thu, 23 Mar 2017 09:46:02 -0700 In-Reply-To: Comments: In reply to Sebastian Gniazdowski "Re: An idea for fast "last-N-lines" read" (Mar 23, 11:17am) References: <1490076282.321781.918060736.22D2C432@webmail.messagingengine.com> <170322205304.ZM5853@torch.brasslantern.com> X-Mailer: OpenZMail Classic (0.9.2 24April2005) To: zsh-workers@zsh.org Subject: Re: An idea for fast "last-N-lines" read MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii On Mar 23, 11:17am, Sebastian Gniazdowski wrote: } Subject: Re: An idea for fast "last-N-lines" read } } % lines=(); typeset -F SECONDS=0; lines=( "${(@f)${${mapfile[input.db]}[-250000,-1]}}" ); echo $SECONDS, ${#lines} } 0.3925410000, 1536 } } I would expect mapfile to perform little better. The whole file has to get metafied by heap copy before subscripting can be applied ... mapfile was a lot more efficient before we began to need to store parameters in metafied state. Other parameter ops are also going to do pass-by-value even if the base reference is mmap'd, so there will be some constructs where the whole file is copied over and over. Nothing to be done about that without a full rewrite of subst.c ... } Wonder how would sysread perform, and what about metafication when using it. Metafication should be OK, it makes a metafied heap copy just as does mapfile. if you first "sysseek -w end 25000" and then "sysread -s 25000" it should be quite fast, but reading an entire large file may be slower than with mapfile.