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Thu, 13 Dec 2018 02:20:48 -0500 (EST) Subject: Re: Upgrading pg_statistic to handle collation honestly To: Tom Lane , pgsql-hackers@lists.postgresql.org References: <14706.1544630227@sss.pgh.pa.us> From: Peter Eisentraut Openpgp: preference=signencrypt Autocrypt: addr=peter.eisentraut@2ndquadrant.com; prefer-encrypt=mutual; keydata= xsFNBFUUt6kBEADZd9NNTBJbHmAXXJgPGOdd6Q73l80oifIVgn2tRxP9dYkCfTlo/yLqbKTl JNqTcyM6XrJDnB2sMEUGYCewYZXl+9C4bBJWyNqcEI1ae9u71vEq/fknFLArJ+2wN+f7QuRx Q8d94ZJAiJQ5g3fNk2HVeedCQCKP5dCzU+ZLt2dbsx1PDZLjTO9gf+JswWuGFb5wY5PZVM5V hq66Xk7ZJzHuARacza2RT7J2fkMmQBY+kr7L98Perb0GhafnlhXB0PvUB+N3xpmggMfwuhTu BngS/G/r3GvemxJuFxouw8xsMqrsfdksJXA2gLXYtwRCssdPV3PO0rlD9twqDo8URfIJ5fb6 1g/MV8aTOKjg3Q8MpJPtkwJqN4o3PvbwYdedeFnOVkkYAJdu/aX1v1BeCBDu7Hy3sF52scD3 pQbyQSl9vUDpTLarASAxNbAV0NRJE8dp4vfW6AH1ccryGiFqw/czPK/iN0+MT8wsjAW6WW4w hvjm5UPA1KTwi3ZT8eT5uycuH7QpuNk7LnGGXQ6KaRALFywzkr0A0V0AvFNa+l4wstMaXaB6 dmMXyF0/hfryqyOeu1gAdq4q0/PNC2dPgb/6uoh4eMjN6A5GXcprilhz5DulmsilY21hfSoU S64ODed96pKhprsOxjZiDRsN1QM5MwB+uwVWUNfsX7fIxE0BrwARAQABzSdQZXRlciBFaXNl bnRyYXV0IDxwZXRlckBlaXNlbnRyYXV0Lm9yZz7CwXoEEwEIACQCGwMFCwkIBwMFFQoJCAsF FgIDAQACHgECF4AFAlUUuKQCGQEACgkQoZ8SQ+xBJp8llw//RbGoXnF72FZTlOFsnNyxnWbF vViPCfdAlZl1GGK9OYCvV1dp/956HuhB0wpaGQHiBmQfOPJf/jLOPjXFYm2iEChEycrBChuE j4TSYemMp5BSPILYk9Uwd16kVD/+U6fQfK6H5pOhfBvbM6asMnmpY2wQuvktxHvaGlytFw84 EzFWNZtAZfxkw28w3AhIQkKe9hJanfyDL750RcbyEr8AAHty5IErrvS7tM5vQwIeh5BF26ND CyKPRdZgOgMpcwFfROKBDpAt052CgWIpNdhBdfIKlkCs4/ILxmC3rT/Mb/qZiHcoMMwEu6k+ T7vRAFZZAk62Yrr/U8/vUGKlzRZQoo86fyojCfI0ibCIc0z8rwCVY9P40G9wD9BTCZS/z8Vh jjpBlNnIKw2hM6hbxavKndCJjFFJD08rXrTyrLF/of18xD37vNdYooP9VATB5QjOWFRrscSZ 4a89e+to3m7YVnd4xdXwGp47dYusoax84C8tg1gZrH38ol9dPmnKX6GZrXeS7tH9k8VeUpJ8 HQbRThQRWAT936QpYbLConBmOtmbLmjQOGtiXPo1oK57X/7U/WBja5vWmm2q+Yxtt+3uHGVg DdDU4CJpXo4lX0v2n3QV5EBSW9hjdF3bNfl6GFBb1pPEhqNcMDUc7zkx/2uENdAdk/BnqMgH umip7b0pVfvOwU0EVRS3qQEQAJf6p0P7D+hMYUgCPkvgrcz6OJYsAYdUMUmokfqmkKwK0oJM ew8TNGM53ocKAgQGma5f10rwbZNPlpVPNRX5hwUmwVlcwSut0oE+JfUBH7mpysWvpF05RKIy q9RCoJZrAbXS7Tig56A1QD8IcM00rERZMcCOlI1+q9m4u9AOI+0LyGGSH+VvoyDHD/Jew4R2 TmPEF8Pu7lYiNYK88Q6u0kBkc+Tz3BNlyc6fi3HxnFfp0b75HLXPSTu2SwA/0Q31wHZXwrEU BR9KgSn/qbgy8ydPc97i82fhiFE3cbGexfPrQSMYmDGi+dcQ0s+AMQwC3XyMC0JkHpYUuFkR QdlIvaIhgFUUN2Vr4xF2ADaNTNFc4DYaiPHFAgHZw+3pZWqS4uIiWgJynrEaHw4F3QWU8/JB iyEWDhNq4WBrRA0u914TCCAoFOOKMnRdl8eJrRQKM/5/lXbHFjjlI/LDKhLRFsuQsnJJ3331 RjCzpHPZG5/p5KR1RHiAXa0p/DW5lXyq21hS3kjDlleoHqOxCN/cy0Jgz7qLDq1vZoCl67Sy RAH60c2Xu4may9SVltmot0OzWVHdrfS+85FQGp9580DaeLio7YMFKy2bfEvwQJ/c9xD2QPB+ oSb3V8ueSznXBG5+dyfOsZFRPxceA0wA2rSWZSjxLdKxvyGTj9vsCjaDu13rABEBAAHCwV8E GAEIAAkFAlUUt6kCGwwACgkQoZ8SQ+xBJp+HJhAAxmSTsC5y7p9Zu+nnLpucv/h88oEx985e qWeXzQiwM3pfRZS+PdTH9TyzHK0KOgKoAiubk0vt+BrT91D9d0G5kVQaTctAErGBoMkTaZJT XVEcNphiPzysdSqvprjojMp1y7rG8AP+Xd6m0rE1LRnkRRm8HyI8vdXsuLQPITGWXDLMjaNq AOV3BUnzkgtjMuIYw7SCr+12ZOb5dEKvaG4kjC4kaJ/TLbuBhVANcXkC90yp0AOZLs/cB1Dj OAXno/RUUruJ3r27a+pFv768UAi9QWcdw58yPxreMNMLqAgsS9oTHwHfGNWcB2dJ4UW+GMLJ hTf9TjQ2f+N/sIx5XMQ9pYw6CAJMK29qPx6/ZayrPxf22EXf0D3zTwIEZgwfSkynFVwV25L7 awQq60fifdMYheSxq7GbhpsixmcD+e161cCmLIt75YDt5bQ0B1yf7EmxG8n7pGZAOM6LoNsU fkSldba5XVwh8LuN5mK0nQBELGW6Os4TDq4REggLpfcvFC215zpuo0iCGnmE/Bns4nowqUSP u4tkWL+nxW4qgv8wo8HJ52jd79EJ8iqfIBoidBfy9AIUiEUApGQzWPu6yWcI8fY0rN5D+tc+ Yw1Zt6Mm+huYJpgCRsTcfzEcahnBn521CWcWvhW1ff3KFileFMtNmnBBhMncmRKHphtTKEpN 3jI= Organization: 2ndQuadrant Message-ID: <6e3eddc2-5084-e0c9-43bc-39649efd5331@2ndquadrant.com> Date: Thu, 13 Dec 2018 08:20:47 +0100 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <14706.1544630227@sss.pgh.pa.us> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit List-Id: List-Help: List-Subscribe: List-Post: List-Owner: List-Archive: Precedence: bulk On 12/12/2018 16:57, Tom Lane wrote: > Attached is a draft patch for same. It adds storage to pg_statistic > to record the collation of each statistics "slot". A plausible > alternative design would be to just say "look at the collation of the > underlying column", but that would require extra catcache lookups in > the selectivity functions that need the info. That looks like a good approach to me. > Doing it like this also > makes it theoretically feasible to track stats computed with respect > to different collations for the same column, though I'm not really > convinced that we'd ever do that. It's a good option to keep around. Maybe someday extended statistics could be used to ask for additional statistics to be collected. > * Probably this conflicts to some extent with Peter's "Reorganize > collation lookup" patch, but I haven't studied that yet. I've looked it over, and it's nothing that can't be easily fixed up. In fact, it simplifies a few things, so I'm in favor of moving your patch along first. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services