Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gLJJC-0000Le-Hd for pgsql-committers@arkaria.postgresql.org; Sat, 10 Nov 2018 02:47:38 +0000 Received: from localhost ([127.0.0.1] helo=malur.postgresql.org) by malur.postgresql.org with esmtp (Exim 4.89) (envelope-from ) id 1gLJH2-0004iT-RD for pgsql-committers@arkaria.postgresql.org; Sat, 10 Nov 2018 02:45:24 +0000 Received: from makus.postgresql.org ([2001:4800:3e1:1::229]) by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gLJH2-0004h8-Iw for pgsql-committers@lists.postgresql.org; Sat, 10 Nov 2018 02:45:24 +0000 Received: from mail.thelabyrinth.net ([45.56.70.56]) by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256) (Exim 4.89) (envelope-from ) id 1gLJGz-0000dE-A4 for pgsql-committers@postgresql.org; Sat, 10 Nov 2018 02:45:22 +0000 Received: from Davids-iMac.local (c-73-39-99-224.hsd1.va.comcast.net [73.39.99.224]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: dsteele) by mail.thelabyrinth.net (Postfix) with ESMTPSA id BEDCA54666; Sat, 10 Nov 2018 02:45:19 +0000 (UTC) Subject: Re: pgsql: Make WAL segment size configurable at initdb time. From: David Steele To: Andres Freund Cc: pgsql-committers@postgresql.org References: <68ea97d6-2ed9-f339-e57d-ab3a33caf3b1@pgmasters.net> <20181005165447.zyzglieznybyi7wu@alap3.anarazel.de> Openpgp: preference=signencrypt Autocrypt: addr=david@pgmasters.net; prefer-encrypt=mutual; keydata= xsFNBFSheh0BEADGNb3c1kOaX5OGUDhqHTwJ3JW7XAllfWLdknpRg+/fihgLPPRnQHZhjq28 nmMLqM+C8TjezT2BgVACeu8qqASnuzN/E5+bAl9hVcgCP4eV/lEIWwVxmhcHqSdeWqWZSBRB tf07fLBnz22+3LwVsESN+fanWxnoqqvE0+hyGnCEDhOBkihgbYHuq4vw1+xgoGN1uDk4NShV El0ZWO90P4e5mOWA2Zsex+8YhGJlfRwMpU69okFCvjpWJKE+ufeJdlrxEpSSKW7SQ0kG1VF7 CvDKpF70TCWkb4Bagb6c7lwZrMjxuBnlIvOlV3RRY67PAaVIFRRvQJeJABOPHp8HnH8cwici 7gwwfWBrZZeAdPqs6VNjANqI9uaDasRnD3yHP6CcHIAeCl5hYnzNTkIqBRlnmD5y8s0VRDLr 6JR3FxscOsvwXPJ+He1RpRlxQDlBboaRFUz8endeQHhGUeHyekQcSYUaz4PX3OJBG0Xi7nr8 EOP6zOeP61z3dL8NuO3QjgPiygvS0qwMEPvOYo52nEGYn08nvFVajI8yxOXFnIwnmpgr5gdq nL9ga72tvSyJQAUx+YB7r1bKjRn/Mlt/fPIS5PXONofiO1K8uX+pzvIX6dnm7ihpFf1XC+uG 5+DKBnU7yS7jCRL52GxWHbuC3mT4tvzqH2b13TLng1Y7Izi+hwARAQABzSJEYXZpZCBTdGVl bGUgPGRhdmlkQHBnbWFzdGVycy5uZXQ+wsF5BBMBCAAjAhsDAh4BAheABQsJCAcDBRUKCQgL BBYCAwEFAlShuEECGQEACgkQn830JKJznPPsLhAAtKkIu0mFfxcVqApg4PNjZKYY4TWeN+I+ go/VKX8QWMadr33t8Sxcgyn48bjBYzgWQXhF4rMcFxDxI3ly5bdE8QKZkhFJJT7N2fBoo9Zm ZOsOvPd+5hz07VZpgNSiTXMAphj8+GSTLbYufm/OUnfpS1eovPtPdYPQpNC3RVHA0gtisz26 NgMLg6QN0iQuITs9N+wiaGtyVIornl4XAY2dM/Hvfr1aDFkukNNr52sc/mGqocG/dKC7dONA 3860y2MLszQcbAE45iEkmwpGkvxyc3i3tvdD3VNlVI1MKJUBnxFPUEI0lVq5WpApFSIU31+j aNunKIcfVxRnM8FTJBsw3RnFRpSsEtiLaZRm5sOZHa9+dy/DWDb+8O1I+momCo88+Jksd6pZ 2Tz9msOiJiTnFsCZgfbbmayH6w8ZyfHuO0DuxScM1UK+6CLC2VVjQFuH6WHqJpaENg5INswS qpUc05iC4i+6dZOe44cviX6LpHuP8vWM0E63CMun0l42yHWy+k6nLvx/fj7t++tF2JIJ92OG n/2MkM5lIKknRg27UjYAspD6f3NSZUMIe6tGyWPTtLOu8zOL5CeRyCHMWwUVDKJSBzlK2mV8 e0EbmtUJFsoNWXWKPKUIxX7JXPN3v523HmOhtyz5SnkGtwEqCZiv/JccYmh+S2IokAuscLNP EJrOwU0EVKF6HQEQALPpUsP67xfcj6NUMyySXSytUzMIVi5XNTyazuNcVfFZzT9QL8wFQkgy i/HOD3tmvdGxz6H8V+v+cszp88gCd8TwClss7u+iPsLlAQQWC4q0WiX4OhwFv2H004iuft8i odjiWDkYEgIFxlPNxQfHFmchkyODIJXQmnzbgsXwGZtJzAxEVh6AgYJqE/Ev/+kTJhJ7703n oIb+PXvafoB5axnU4nf7DuFa9X+q2/ZfzyAXUCKvzDvxb24iUgWFzlWBx0CnI21Kh6aS6hR6 o00D2OBiU+yCpW9eRTi3SuDuslmtCUaZz5V4SHo37ochEYfZ2LYOPsBO3PUMx8T7MDYrmv/x 4W5rdjugz4NXWROStNNLpS74LW20rdrEKMDltph7U2zfjjS663K+CUxoXn/ha2WnzBocoY5o KwdViLln4s0ivOTa4clHJJUsYiAxLShAe2AP+5kJim24tAabbEOsrRTn9RpT7J8jVT/G0YDE glujEt0U04Akkj5NO4G7vJP/AyX5zKZetkp/HFiFBZMkUuXD/KgDc5EM2fpQtaxGGY2fcQqY VHUbbxstxyl5d349M9rok7O90hw9BkP0Q8UEpgmlZ6ftwx+ZfZmBEdQ7HcMHnSPSNJkXt/Vi ozlcrSnkVXzCXvH9DHrIpgenp8btsJ2XyjSdrEu4jAqYeirW+3qRABEBAAHCwV8EGAEIAAkF AlSheh0CGwwACgkQn830JKJznPNmERAApYaQK6i9F6hM2RUD/PqQC45WmzOXK9bDSS9hdk4p Nc5jSW2+FkcMFe1XFG2NyGf1v5KBPxuDTQp35PIwRsL59xNmPICu0ae6zmCPUpxbMIEzb/VU wXqeuNp3cRVll06goDt5w+2LlAtBrxuDjiWxby9LH+vsIUMLWYu+M50pdtOcXOsO1+zyfs3w U6xRZ3PaFDKO1cB68okDFG/cFHnYfY5aETV7LgVBHEOQLwL01U01QC/iqY/aNO4iUH/+PBc0 R6mYlP7IqDQOQVTJ0dXP365thl0Q7c9e2JQSS9wuSv2EEiR//nnZREtLyrQNLwsXE8UFBDe7 uA8Lm2ldmQYpHHKAcorGVTHYJaaus2LjH8tZ1i4RGg4hKMJSHil/5C+Ghl+PmcACVeGaxB0c mJ8+0jyWDkLCDMAXJJyvXRWIONTAxVt5kKg1/iMAq1IQYNd66agnmgxdSvKLPUo0JJ5fhQJp 2bqDDTrINTZg+Rub2HeoOMxYJsMypK+6aY4iVlm2Z7A9SgyQDjGAXzD9+XaezNFeXxfPbjo6 46qA9SycdYhiwaTcTQakiLkZWRIkSjGQwNCK9NktE1fYnXfR0+WaWFduQ4BfM5uta1bt8esB /mLEjVYS9RRAWZ/untJrR9JYGTC4Mu6tcLGZD7385yX3TNM1iaIUGxlKkHHCZCnILyo= Message-ID: Date: Fri, 9 Nov 2018 21:45:18 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk On 10/5/18 1:03 PM, David Steele wrote: > Hi Andres, > > On 10/5/18 5:54 PM, Andres Freund wrote: >> On 2018-09-20 11:48:08 -0400, David Steele wrote: >> >>> diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml >>> index e1073ac6d3..3bfd172441 100644 >>> --- a/doc/src/sgml/config.sgml >>> +++ b/doc/src/sgml/config.sgml >>> @@ -8440,10 +8440,8 @@ dynamic_library_path = >>> 'C:\tools\postgresql;H:\my_project\lib;$libdir' >>>         >>>         >>>          >>> -        Reports the number of blocks (pages) in a WAL segment file. >>> -        The total size of a WAL segment file in bytes is equal to >>> -        wal_segment_size multiplied by >>> wal_block_size; >>> -        by default this is 16MB.  See >> linkend="wal-configuration"/> for >>> +        Reports the size of write ahead log segments. >>> +        The default value is 16MB. See >> linkend="wal-configuration"/> for >>>           more information. >>>          >>>         >> >> Why is this actually more correct? You mean because we have a conversion >> that does the mb conversion at display time? > > In pre-11 versions of Postgres, you get this: > > postgres=# select setting, unit from pg_settings where name = > 'wal_segment_size'; >  setting | unit > ---------+------ >  2048    | 8kB > > But in v11 you get this: > > select setting, unit from pg_settings where name = 'wal_segment_size'; >  setting  | unit > ----------+------ >  16777216 | B > > So, while the WAL segment size used to be expressed in terms of 8K pages > it is now expressed in terms of absolute bytes.  This seemed to me to be > a very deliberate change in the original commit so I guessed it was done > for clarity, but that the docs didn't get the message. Thoughts on this? I know it's minor in the grand scheme of things but it caused me some confusion when I was updating pgBackRest for v11 and I imagine it might do the same for others. -- -David david@pgmasters.net