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 1jxwJE-0005Fa-Rs for pgsql-hackers@arkaria.postgresql.org; Tue, 21 Jul 2020 17:44:08 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.92) (envelope-from ) id 1jxwJB-0004t1-2y for pgsql-hackers@arkaria.postgresql.org; Tue, 21 Jul 2020 17:44:05 +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 1jxwJA-0004st-Lg for pgsql-hackers@lists.postgresql.org; Tue, 21 Jul 2020 17:44:04 +0000 Received: from mail-ed1-x52a.google.com ([2a00:1450:4864:20::52a]) by magus.postgresql.org with esmtps (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1jxwJ3-0001gS-GR for pgsql-hackers@postgresql.org; Tue, 21 Jul 2020 17:44:04 +0000 Received: by mail-ed1-x52a.google.com with SMTP id g20so15885176edm.4 for ; Tue, 21 Jul 2020 10:43:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cybertec-at.20150623.gappssmtp.com; s=20150623; h=from:to:subject:mime-version:content-id:date:message-id; bh=IX8RiMocYcoaYeDSuyUbHi0XAQF8X0/UkpvLS7GywcU=; b=n4WCFPLYKtnO4kZftbQOjvQ0fzUgx4iqxjrDanxoh9rFBIh0lWel+KuIF/DuFh2U0U tvmFuyWAZlnOj/h9+x8bGGFU5DcUJ/TnvnzOP+ZkIgFEhduPVRXXFPY2LLBl64N2G9Hj 0++LIc8s2FfBlbT6SduFJLCMhjkkLzxjkj5N45CEpoy4Cwxof+HbCAyCH5nV/GMYJZi5 V9Vxk1I6Pex9G2KC5octC7H9AV7WpYAlnshPYPvE9TUxalvI4EGkV1nUgETj6m93SXOO Jw0wsOuIX8FyqKgHBfOe9levz/m1rO/ix/pKtfhRAAqqZC+VQvBnSmMsrte4oqeF2Vlm aokg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:subject:mime-version:content-id:date :message-id; bh=IX8RiMocYcoaYeDSuyUbHi0XAQF8X0/UkpvLS7GywcU=; b=ZmUAjx4S351b8JA3KRlnfqRbDILNb7jyDwnX8LACz4GMUBK7ZSQC5eQZ9ziG7jmHgT LAICYz+OZXf12b/PGZWtCeEZciO/EdFrRSRjGPzqEraL2I8ekw33L+9TJ1mI2dvmspSV xX8UtJTgbBZGTv/UE9pgl0p2vpt0Vgejx3Rfvg73Ru3vvtCi7roHfUEmxUGeSeBKx8I6 5g7kdrwNH//05UtYMW0ufHAQhWDYdDiONn6tzTLx2ZAKVEdpOHFiAm7k6SrFR+OmU4OI 0JOBJCbBHPdgmsYRWDnA2Z26SXpHMdvAkwmUVNrKLZ1DKywQ/5uGQ2yQ1KdceIV0B0Yb YeYg== X-Gm-Message-State: AOAM531kayVqCq36J2wVWYw0+dghQAsfNsoDLRkdpEi2irLdT0dLyVIH 1esH8arL33ZpnHVvF1WvpjS8w3YV1+huTg== X-Google-Smtp-Source: ABdhPJwuYVdm9GQhSRhrPH0b3/gkDf7C7307kGvFX/Qr43TqqNYkluys+HOTiwewg6DQ+ciHgSSO1Q== X-Received: by 2002:a05:6402:1d89:: with SMTP id dk9mr26801766edb.31.1595353434557; Tue, 21 Jul 2020 10:43:54 -0700 (PDT) Received: from antos (85-207-121-76.static.bluetone.cz. [85.207.121.76]) by smtp.gmail.com with ESMTPSA id w18sm17480758edv.11.2020.07.21.10.43.53 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jul 2020 10:43:54 -0700 (PDT) From: Antonin Houska To: pgsql-hackers@postgresql.org Subject: xl_heap_header alignment? X-Mailer: MH-E 8.6+git; nmh 1.7; GNU Emacs 26.3.50 MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <21642.1595353537.1@antos> Date: Tue, 21 Jul 2020 19:45:37 +0200 Message-ID: <21643.1595353537@antos> List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk I don't quite understand this part of the comment of the xl_heap_header structure: * NOTE: t_hoff could be recomputed, but we may as well store it because * it will come for free due to alignment considerations. What are the alignment considerations? The WAL code does not appear to assume any alignment, and therefore it uses memcpy() to copy the structure into a local variable before accessing its fields. For example, heap_xlog_insert(). -- Antonin Houska Web: https://www.cybertec-postgresql.com