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[162.239.31.113]) by smtp.gmail.com with ESMTPSA id 3f1490d57ef6-e8fe61e6544sm4905112276.32.2025.08.06.18.12.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Aug 2025 18:12:42 -0700 (PDT) Message-ID: <7fd9f434-e0d9-414b-b396-841ad3c00040@joeconway.com> Date: Wed, 6 Aug 2025 21:12:41 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Safe vm.overcommit_ratio for Large Multi-Instance PostgreSQL Fleet To: Frits Hoogland Cc: Priya V , pgsql-performance@lists.postgresql.org References: <3A250F65-F5DE-4E24-ADE7-BEFF4A18A8B9@gmail.com> Content-Language: en-US From: Joe Conway Autocrypt: addr=mail@joeconway.com; keydata= xsFNBEpXMCsBEADDnXUQzjlyi/cX02Gtdy2CLcroE5CsC7DJKdOBDbfgn0kfiIYoV5JniG4l VyzZUodY8yUAagqLYolh0UkBzs9N+qkm7erde4ypw3jzVQ37BuzIvk3nMUbuDZDgxWqX+nVS sKc+BQ5BpzgCHg48leoRO2ohjvYnUhgH3j2rFZCzaj6qQ7mv+XoxOJmUlVQtG06Jwkk7Vu14 7U9nMMM6hyUKzVnmCphnlcMNo26UyVU70MwFfFJgcI0c5fpp8byN56eD6VJVnufO5WAuEhzE qcrSJR2FAlmM90GBY+6vP29twLDCHuSFvrnujNCx/BvCC/a3/gPvyAFp4JtMm9eXAmq3m/Kw 94nTJXVdcbQeQQDp3KIG7MmWS4lnGvPn8v0CjgNaLvZXFLo1FgmUVsyEq1Lww4iRLa6sbpXJ ESx15UEue1k1YZM9C+4F/o3aeKNsAienjw2EXFzcaxIg/C4P493VMi3Qa8ycVxR5iYhUbYdo DFIUQhbFNsYfrtW/qZAELT3FCYFpZYG01e9Hj+cBrXXgyDDkQ5Lq4mlvmkRvuxn61V6Au4HA 0sJiCox5pM1FvzT+aI8HY1BYaiB9Pl4fhpKgmhhlSuglk9v39S4jmlUIb45iLAUVpeNM6Qjm 69pf5da9sm4aGFa7YlDSKf/WcU7z9ITZxsilOi2n7YJiwG7kTQARAQABzSRKb3NlcGggRSBD b253YXkgPG1haWxAam9lY29ud2F5LmNvbT7CwXoEEwEIACQCGwMCHgECF4AFCwkIBwMFFQoJ CAsFFgIDAQAFAlWTVvUCGQEACgkQMyt+aLaZQ0oPCQ/9HyRewMyvAIJRmoXoLAr8AoFLId6R qBJnNX0Lll0RLZui65aQ0+exwX7aH7TxWR16B2gWX3OmLfGT8XITOoG+zt9zsEpLvNkHchkF T/jyAcbuRj5WX9hamZgMbjXAJeCdlhW+fRA9Upb0w4dgBjqK5OgsqMikASL7t2vogHl9H08j vSoQLW+8wTnSBXBeBTBwB7xLIin5WVivzFHUCrnD2UsjeBIW3fmGdpTAjSxRzG+UPYVwXQ8F FLt7DpEytvLWapmZWMRdj0WZ/Q3SOO/Ed0yFqbzuwKaWcFrQBNeS2Sig+FefBNS98f9Hx7ku H3DW34qX/zSSdDh0jLs7X3PkIgF6BZR2TxaCwHPP9ERDiDaUInC9U7We1iZE1DjW8rLMEVJB hY0ClrrF67pnUKTbcU+uajpPn+2Jl74T0Set/XxpHZ4cezcJuqg31R8vHZgd5cf1WKP0D0pc qiuS02BBFkNCs1jQ+raTWcDuE6F1mUO2nvjUBN9r4y5DUbCNSqLKeAe/aA6JaSDkBpoXKdNS +c4rbzbktWkfUW8EhVlCGzNpy4ezEoVsqV2Ex7fNoxsE2vnSylLT9hycAmYf8ryMvniRZqnD T4JgLenIcQlkhB896T7wApOXfD8OJj1/XFxAfPi6vdlsr81uoxuB4euLp8IyduwLORRUogO9 zmAXG5jOwU0ESlcyJwEQAOkTBb9yDhJbMUgvhM11rZwT5tm4Y9TqtEHn0Zy3t9g7bdFFpMva v/KENd3oAtLFpMDf+H3AggFk4ftUwJwiVgJ88ilvCynJUGXiuYIaexY4DLgn4xpnuiEpYEFV dWnlw7dWVTc62exfqIz9bSWRzwfBCY9ruYGEb4RDPDSNSAVyI7sxHzef2asiYxIcxrTrw5Vu gWNlPZcV5/EJ6PUvATjBF2TBkXV7KOciQng2tsQGrGMkY5mduNqwpuh6zfPcVF8LeObe96wv 5ZhPRpO79nef7hnK2lJogp3JIo558Jlbz9WHtQEMZR85+bUhtI825QyNAFz3Jrn7NMgvDikc 2OrWo7YMgMC5hDSWVFqA6/EQCNnDWGABWgeYHZFpnPwsvUWIYdhSilUuj/Tuzvz9ZmucFNbQ bauDQw6VQ38ofGnoYDZFJsGncprB8dBi4tDrIQ+1RlIh6C2Z/eMipqJOT26+spluTjouvnKT 0S5yOgyX0PjbsysgwQdCGNJLHOjhHbSpSmOLaduV3CQo/0+DHT/TBjYfIXjTWouY9TkGxG4e NrxU0u2xAy5bMqOPmsFdjLTWlQUlF/fTMhB54XwI3FHWgnSnXZzStDTmTebLNdT/ftgliAzA 81uMj49j0exv731/v+7udLA1bV8gnZ01zQCASDpWiRQR3fgwcugSUqgRABEBAAHCwV8EGAEI AAkFAkpXMicCGwwACgkQMyt+aLaZQ0pwAQ//bjcWnZg/jjRQ9gbZUGMqniItZYRglBMKIqt4 Fia379JmHwTvavnFkJ8XMZ56UB0FIrgS+sUkRH6cPRQR+7Qi392LD021DXgSsz9CwFHjFyBG HwLEOTRcfYQbtJy0shHDJB4aQTOX3ERDH1PsvJNuevmQMzS0DWFav9+xMz9rKP4N+HffoBIZ E0C1xIE43nD4eLsbycte9sVIrmlNuUti3qUxJAQw8HwfJ6ZbBInHxquApR16uD1u99o6Xlnd FrDlY22tRmHCM0bR81GfGNdcU3Uo+rG/R/k4qa7s9/dgKvMbyH3fHhp/ceKag80Xo8IFurRl 0ZJP3sHJ2QDHCVLat7jRZ+43hi1WlIhFbrgn6IyI0i7XR/W8JjrC5MsKq4TUwGH077sU/kcH YebVJZRbUUst2hAGHDFVBcG12qoKf+ltL9qXJc1y7BGeCoUW6QjOpljpq6ZL4FQUsM0RSRjs 5egE3szPcIf5SyPK6WDOApoAq6M7BBFMGDZwEylYMtr0YekA1u86UA9D2xwLHEbBBp/uiby1 c9JbPJ1Pn8zJP8WZNeRw4Q9TtqVK09+oLirMUSpIDd6KdZ1VgRxOK2re7tjDvkVuYsSrsiJ+ 1iJNEnp9iK0ok0DlJpSCe6KhkxpaTdeoWMXdKuJWec0NIqoAd54ZgBPnr+UPxTixgPq/p6Q= In-Reply-To: <3A250F65-F5DE-4E24-ADE7-BEFF4A18A8B9@gmail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Archived-At: Precedence: bulk On 8/6/25 17:14, Frits Hoogland wrote: >> As I said, do not disable swap. You don't need a huge amount, but >> maybe 16 GB or so would do it. > Joe, please, can you state a technical reason for saying this? > All you are saying is ‘don’t do this’. > > I’ve stated my reasons for why this doesn’t make sense, and you don’t give any reason. What do you call the below? >> Op 6 aug 2025 om 18:33 heeft Joe Conway het volgende geschreven: >> * Swap is what is used when anonymous memory must be reclaimed to >> allow for an allocation of anonymous memory. >> >> * The Linux kernel will aggressively use all available memory for >> file buffers, pushing usage against the limits. >> >> * Especially in the older 4 series kernels, file buffers often >> cannot be reclaimed fast enough >> >> * With no swap and a large-ish anonymous memory request, it is >> easy to push over the limit to cause the OOM killer to strike. >> >> * On the other hand, with swap enabled anon memory can be >> reclaimed giving the kernel more time to deal with file buffer >> reclamation. >> >> At least that is what I have observed. If you don't think that is adequate technical reason, feel free to ignore my advice. -- Joe Conway PostgreSQL Contributors Team Amazon Web Services: https://aws.amazon.com