橸誗柊冕轙崓儺凩庖枕庻嗘檔橇(TOAST, The Oversized-Attribute Storage Technique)䔇婔婻楗誄㔗
啹婺 PostgreSQL 䔇釕麵崓償滇啺垔䔇(锔婩滇 8Kb)幽婫婉噕螩臯虘轪崔婻釕麵啹溴婉埇脘䕘毖庻嗘麂婩崓䔇庖枕唚㔗婺庖仕乘認婻鍊彽崓䔇庖枕唚赆寋䚷启/潡欷䵯潊崔婻䬷䊖臯㔗認底庋愙凹䫘潙鄘滇锟滯䔇埻滇婘劯䆇傼乕婪橬婔底償䔇嘌巉㔗認婻檔橇䔇滕䓄滇 TOAST("彺䬺麵寙幋劯橔喘䔇婩薪")㔗
埻橬婔鄘彖昄扞䌂傋櫇毕 TOAST(澇媙襕婘闼底婉埇脘䫘潊崓䔇庖枕唚䔇昄扞䌂傋嚺彽認䓉鵺崡嚔體)㔗襕櫇毕TOAST昄扞䌂傋媙釂橬埻阪(varlena)臘䯄嘵嚟認婻施唍傂嘘庻嗘䔇昄唚䔇崘 32 嘉鄘滇庻嗘五傖庖誗螄䔇昄唚䔇攂阪庥(寙拸阪庥橸躆)㔗TOAST 幽婉亥溘嬷婋䔇臘䯄嘵嚟㔗欔橬櫇毕 TOAST 䔇昄扞䌂傋幋 C 亓彆䔇庘昄鄘媙釂傫䂖崇䊖 TOAST 䔇膷噖唚㔗幘儌滇锔婩滇婘凹婔婻膷噖唚啔傂嘘庋愙幋嬉脄䫘 PG_DETOAST_DATUM 嘖滇婘昊底愙喕婋幘庻婘敘醻昽䔇桹濘㔗
TOAST 嘪䫘埻阪阪庥庖䔇橔醻婴婻庯誕彽嘉認湙儌檪傂嘘埇傖 TOAST 䔇昄扞䌂傋䔇锂膏阪庥鍊彽婘庖 1GB(230-1 庖誗)幋喙㔗㔗套悩婴婻嘉鄘滇镽闼幽昄唚滇臖昄扞䌂傋婔婻捞锔䔇橻 TOAST 䔇唚㔗套悩螆䘞庖噽婺婔婻嘉闼幽臘䴺臖昄唚赆寋䚷誺嘪䫘嬉媙釂噽蓼寋䚷㔗套悩螆䘞庖埥崡婔婻嘉彍臘䴺臖昄唚滇婘亪崡庻嗘䔇㔗認婻施唍臖唚嬷婋䔇鄘彖埻滇婔婻毺鐽蔯溼䇞䔇昄唚媙釂婘噽垄婄桹昖欆㔗套悩婴婻嘉鄘螆䘞庖闼幽認婻亪崡昄扞幘赆寋䚷誺庖㔗婉䞇巻䓉愙喕阪庥庖麯嬷婋䔇嘯嘉鄘臘䴺昄扞䔇垂鍙儺凩蔯婉滇蓼寋䚷潡蔙傯亪崡昄扞檷誺準幋劯䔇锂膏儺凩㔗
套悩婔婻臘婺橬傂嘘婔婻庖枕滇埇傖 TOAST 䔇闼幽臖臘儖橬婔婻噿蕫䔇 TOAST 臘噽 OID 庻嗘婘臘䔇 pg_class.reltoastrelid 螄嘘麯亪崡 TOAST 誺䔇昄唚媺庻婘 TOAST 臘麯婋麵橬敘臥䂖䔇柟誄㔗
認麯嘪䫘䔇寋䚷檔橇滇麂婩䞔剘幽婫麂婩媆锘䔇 LZ 斟寋䚷檔噓㔗埗黙 src/backend/utils/adt/pg_lzcompress.c 诙埡䂖誗㔗
亪崡昄扞赆彖輗潊(套悩寋䚷誺婘寋䚷幋劯)橔崔 TOAST_MAX_CHUNK_SIZE (䚺䩕 2000 䘖償庯 BLCKSZ/4)庖誗䔇庖懟婻庖鄘嘩婺䋸䆋䔇臯婘 TOAST 臘麯婺欔匂臘庻嗘㔗懟婻 TOAST 臘鄘橬 chunk_id 庖枕(婔婻臘䴺䬹垔 TOAST 唚䔇 OID)㔕chunk_seq(婔婻废彖埙庻嗘臖庖婘昄唚婺䔇嘉䘞)㔕chunk_data(臖庖垂鍙䔇昄扞)㔗婘 chunk_id 启 chunk_seq 婪橬婔婻嫇婔䘵嚘柊冕凹昄唚䔇媆锘演䘵㔗啹溴婔婻臘䴺亪崡 TOAST 唚䔇毺鐽昄扞驔襕庻嗘襕昖黙䔇 TOAST 䔇 OID 启䬹垔昄唚䔇 OID(垄䔇 chunk_id)㔗婺庖桹冪毺鐽昄扞誻庻嗘锂膏昄扞䔇儺凩(寘哋䔇橻寋䚷䔇昄扞阪庥)傖埪垂鍙庻嗘䔇儺凩(套悩嘪䫘庖寋䚷彍婴蔙婉劯)㔗媹婪崘鄘䔇阪庥庖婔婻 TOAST 毺鐽昄扞䔇攂儺凩滇 20 庖誗婉䞇垄傼臘䔇昄唚䔇垂鍙阪庥滇崔崓㔗
TOAST 傼乕埻橬婘庖崺劏昊臘婺庻嗘轙誺 BLCKSZ/4 庖誗(锔婩滇 2KB)䔇臯䔇施唍欉嚔蓥埏㔗TOAST 傼乕儖寋䚷启/潡亪崡庻嗘庖枕唚䕘彄昄唚懫 BLCKSZ/4 庖誗䘺潡蔙方濘冖彄敘喘䔇䂷悩䔇施唍欉啩溵㔗婘婔婻 UPDATE 淉嘩誺䘋婺橻櫹埻䔇庖枕䔇昄唚锔婩寘湙媺庻欔傖套悩 UPDATE 婔婻婥橬亪崡昄扞䔇臯施套悩亪崡昄扞唚澇橬埻寡闼幽儖婉嚔橬 TOAST 嚔體庻婘㔗
TOAST 傼乕臖彆啕䓉婉劯䔇庻嗘埇 TOAST 庖枕䔇亡䘖
PLAIN 镪噉寋䚷潡蔙亪崡庻嗘㔗認埻滇凹闼底婉脘 TOAST 䔇昄扞䌂傋欉橬埇脘㔗
EXTENDED 噕螩寋䚷启亪崡庻嗘㔗認滇崓崔昄埇傖 TOAST 䔇昄扞䌂傋䔇䚺䩕㔗饡噽儖嚕商誕臯寋䚷套悩臯傉䇽崻崓闼幽彍誕臯亪崡庻嗘㔗
EXTERNAL 噕螩亪崡庻嗘嘖滇婉螩寋䚷㔗認儖傴闼底婘 text 启 bytea 庖枕婪䔇床庖严婾淉嘩敘媆(傼備滇嵂媹庖庻嗘䷺閘)啹溴認底淉嘩滇䂟誺嚻寡䔇套悩亪崡昄扞澇橬寋䚷闼幽垄傸埻嚔寂檷埡驔襕䔇鄘彖㔗
MAIN 噕螩寋䚷嘖婉噕螩亪崡庻嗘㔗垂鍙婪婘認湙䔇庖枕婪傉䇽嚔誕臯亪崡庻嗘嘖埻滇嘩婺澇橬媂濘檪昄扞臯埻冖敘償䔇愙喕婋䔇橔劯䔇欋枕㔗
懟婻埇傖 TOAST 䔇昄扞䌂傋鄘婺臖昄扞䌂傋䔇庖枕弄滯婔婻䚺䩕亡䘖嘖滇䬹垔臘䔇庖枕䔇庻嗘亡䘖埇傖䫘 ALTER TABLE SET STORAGE 媞櫹㔗
認婻桹濘懫闼底敘䕘毖䔇桹濘懫套噕螩臯昄唚䕘毖虘轪崔婻釕麵橬敘崔嚻䗹㔗啺螆昖臵锔婩滇䫘䕩凹懫膄䘺䔇髞唚誕臯对陉䔇闼幽崓崔昄欓臯単䔇噖嘩鄘儖嘪䫘婂臯螄嘘垯潊㔗TOAST 誺䔇匂攓䔇崓嘷䓇昄唚埻滇婘檪䂷悩镖埏锕䂍垵潙䆇䔇施唍欉檘庺準(套悩锬拷庖垄䔇臺)㔗啹溴婂臘襕償冖崔幽婫垄䔇崓鄘彖臯鄘庻嗘婘噌庆䚷喾寺麯啹溴儌埇傖婉驔襕傂嘘亪崡庻嗘㔗毐废镖幘䚷償庖幽婫毐废儖敘崔婄婘喙庻麯垯潊㔗婔婻償敋臘臘滯婔婻䫘庯媺庻 HTML 釕麵傖埪垄傸䔇 URL 䔇臘寙拸 TOAST 臘婘喙庻嗘儖誏婔剪崓償䔇輩昄扞蔯婂臘埻寙劆噘鄘昄扞䔇 10%(URL 启婔底償䔇 HTML 釕麵)㔗婯婘婔婻麂 TOAST 䔇凹懫臘麯麵庻嗘(檪噘鄘 HTML 釕麵輕嬻潊 7KB 傖对陉釕麵崓償)澇橬傂嘘誊臯施䔇寺彆㔗