Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jhKv0-0007HY-Qm for pgsql-hackers@arkaria.postgresql.org; Fri, 05 Jun 2020 22:34:30 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.92) (envelope-from ) id 1jhKuz-00013P-AY for pgsql-hackers@arkaria.postgresql.org; Fri, 05 Jun 2020 22:34:29 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jhKuz-00013H-3S for pgsql-hackers@lists.postgresql.org; Fri, 05 Jun 2020 22:34:29 +0000 Received: from mail-ed1-x542.google.com ([2a00:1450:4864:20::542]) by magus.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jhKuw-0007O5-4I for pgsql-hackers@postgresql.org; Fri, 05 Jun 2020 22:34:28 +0000 Received: by mail-ed1-x542.google.com with SMTP id q13so8648803edi.3 for ; Fri, 05 Jun 2020 15:34:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=2ndquadrant-com.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=xMbBNReNCBru/aJqpIWueeRSQbA89GFCtiyl3l4Ojus=; b=ZLLQEzuKnStlLPZ9yE/R262i78zjYhBN/G+lafKyKf9bcpKnU40/7XBgG1G5MQPRBP ovgxarzpWessW+/K4AMVJoNhF+8koLNSYxdHOL5qtuueNHaFzsZ+MVn51M2tH8ZKULZ8 dnU38I6x4by4XkoB7zIht4WFKJllpaAc9q22CmuQA2ZD+X9Mz5lOrZ57x0wBqKglhRzw 4KMxFUafwG3l+apMTPKjaC0wX2etfjwfXr8IfoTUfnWnjnleGp14DOZRyhYBlJcntfBh 65QmGdmFA28PDIYegb5hQK58c6bWD99YUUMM8q3holNCmjy+nBX87/edNpgsKsn3TORv jYCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=xMbBNReNCBru/aJqpIWueeRSQbA89GFCtiyl3l4Ojus=; b=hswdVbnzhs/7U/0qnvLpQ8+zw7+WSm2dGL1eWYUa24uA7lK2Xp6VphiKIyT3/+2pIE UgrqCuM6qVQDSM+yMkAI15g7OmV4L4nxTUP1/zjNCN4gEXZUgvb0xoUWfCXmGBXJbNFU W0bkfrUOMzcPfivetjnUZFTmH7SNWUQit8EkW9LdRO7tFckwBMSfgjJXPTXJN5hGtpmr xHhEeVZTDlaQczTyjfNWLDDOBvGXylNogF1bcDGYVsRHZSFS0sTqtg7FCgZU7wE8xGqX rqxS0P0l1t9HqfXj2SS3VaP5jjQkvVVWgWeyT4t/u/H2ZAuOGBaKXoT1dvarFU2asnH2 KqHg== X-Gm-Message-State: AOAM533FIJ1xAswkjHdqbTU7ZKIAUJDuAaODd9EEEG1kyQKllkxFirvI 5/DeNy/OD0rvczyLeagY4bzF1A== X-Google-Smtp-Source: ABdhPJwHos5FcX8sxC4SZjhHKfDUiAgVQfzIunazt3gkQfo25I8u5+9LFBYqUG+TcrJa4K/jX4U3CA== X-Received: by 2002:a50:f052:: with SMTP id u18mr11139959edl.16.1591396464969; Fri, 05 Jun 2020 15:34:24 -0700 (PDT) Received: from localhost (ip-86-49-253-141.net.upcbroadband.cz. [86.49.253.141]) by smtp.gmail.com with ESMTPSA id gt26sm5285561ejb.107.2020.06.05.15.34.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 05 Jun 2020 15:34:24 -0700 (PDT) Date: Sat, 6 Jun 2020 00:34:22 +0200 From: Tomas Vondra To: Thomas Munro Cc: Dmitry Dolgov <9erthalion6@gmail.com>, David Steele , Andres Freund , Alvaro Herrera , pgsql-hackers Subject: Re: WIP: WAL prefetch (another approach) Message-ID: <20200605223422.r76a5rpl2zg2xo34@development> References: <226b5950-7404-a51d-8dc7-53895b363a38@pgmasters.net> <20200419114820.h62ryte7uwu46e2x@localhost> <20200425191935.4p6qxzzu5bklodwk@localhost> <20200502151423.yf52i63u232fdfrg@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk Hi, I wonder if we can collect some stats to measure how effective the prefetching actually is. Ultimately we want something like cache hit ratio, but we're only preloading into page cache, so we can't easily measure that. Perhaps we could measure I/O timings in redo, though? regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services