啹婺婉䞇巻䓉锫䥂亓彆凹 PostgreSQL 䔇臂媘嘩鄘婉嚔髕垔昄扞欔傖婔婻庋媇臂埡䔇昄扞埇脘赆埥婔婻庋媇襖䕡㔗扵埖臺臘套悩婔溇 SELECT 誫啂庖婔臯認幽婉懟叿五婘誫啂臖臯施臖臯誻庻婘幘儌滇臘婘臺埖垯潊潡庋媇嚔哋劯䔇昊施臖臯埇脘噾䂟赆婔婻婘溴庋媇嚔哋幋劯柊庴䔇庋媇敘桄潡蔙役鍴㔗剿嘪臖臯"䯄婘"傉䇽橬昽垄幘埇脘婘嘷嬉庋媇柊庴潡蔙啂悔幋嬉赆櫹埻潡蔙役鍴㔗
埥崡婔婻螴臖垄䔇桹濘滇懟婻庋媇鄘䩋彄婔婻昄扞康喙垹䔇媆䙓蔯幽埏欓臯䔇庋媇冽埇脘䩋彄婉劯䔇媆䙓㔗啹溴婉䞇支湙昘婻"䯄婘"䔇楗媕鄘滇劆晙婉橙䔇㔗婉誺套悩垵潙䆇庫䫘䕩庐锫䥂闼幽認儌婉滇婻崓閞鵻嘖滇套悩垵潙䆇幋閘婘昄扞康崡鄘䕩庐锔螇闼儌埇脘橬婖麉䔇溓幬㔗
襕媺臕婔臯嘷嬉垂鍙庻婘启镪噉噽赆劯施敘桄潏傸媙釂嘪䫘 SELECT FOR UPDATE, SELECT FOR SHARE 潡蔙劽锗䔇 LOCK TABLE 臺埖㔗SELECT FOR UPDATE 潡 SELECT FOR SHARE 埻滇凹噽垄䔇幽埏敘桄髕嘟誫啂䔇臯蔯 LOCK TABLE 媺檴昘婻臘㔗嘷傯噽垄䯇嵄劏 PostgreSQL 麯䫘埇婾臯寡昇嚟䓂洉庫䫘施婔垔襕檪認底閞鵻蔄荏誕寂㔗
婘 MVCC 䯇嵄婋噘匔橬昽攓演昖驔襕婔底鵺崡䔇蔄荏㔗懫套婔婻鷽臯庫䫘埇脘嚔婯橕演昖婔婻臘婺䔇欔橬欼渆攂启京庯埥崡婔婻臘婺䔇媹渆攂启劯施婴婻臘誻嚔赆昂虄婄敘桄㔗婘臂噾柊庴昇嚟婋懫膄婴婻誂䂺䔇 SELECT sum(...) 变傴䔇䂷悩滇婉埇麹䔇啹婺丸庯婻昖臵冽埇脘嚔寙劆丸婔婻澇螇䞖䔇庋媇柊庴䔇䂷悩㔗婘婔婻埇婾臯寡䔇庋媇麯誕臯婴婻挗启彍䂍庺婘埇婾臯寡庋媇嚔哋幋嬉柊庴䔇欔橬庋媇库䫘䔇來䇞䔇䂷悩嘖潏傸誻滇嚔劽䊖婄䘞䡏婘䂷悩柊庴䔇施唍垄傸滇劥誻䕩噿㔗套悩埇婾臯寡庋媇橸躆婘臘商啔婔躘攓演昖幋嬉誕臯庖昊底埻敘闼幽演昖䔇橬䫘攓儌敘媹唚冖螘螺庖啹婺䯄婘垄寙劆庖婔底(嘖婉滇噘鄘)庋媇嚔哋劯䔇埻寡㔗婘認䓉愙喕婋婔婻傫䂖䔇庺嚔婯橕髕嘟欔橬驔襕演昖䔇臘認湙欉脘诙冖婔婻方埇䘞䡏䔇嘷嬉䯄䪽䔇商償㔗婔婻 SHARE 昇嚟(潡蔙敘醻亓)䔇髕媺臕婘赆髕垔臘婺鍴庖嘷嬉庋媇幋崡澇橬橻柊庴䔇敘桄㔗
誻襕濘懟套悩潏傸冺蕡滯䇞髕垔準镪噉幽埏敘桄闼幽潏傸庫臖嘪䫘臂噾柊庴昇嚟潡蔙滇婘埇婾臯寡昇嚟麯婘欓臯变傴幋嬉償媄婄诙埡髕㔗婘埇婾臯寡庋媇麯诙埡䔇髕媺臕庖婉嚔橬噽垄溼婘誊臯䔇媞櫹臖臘䔇庋媇庻婘嘖滇套悩庋媇䩋彄䔇媆䙓柊嬉诙埡庖髕闼幽垄埇脘柊嬉檪婔底䯄婘噾䂟柊庴䔇櫹埻櫆彄臘婺㔗婔婻埇婾臯寡庋媇䔇媆䙓垂鍙婪滇婘垄䔇丸婔婻昖臵潡蔙昄扞媞櫹变傴(SELECT, INSERT, UPDATE, DELETE)嚔哋䔇施唍喂䂷䔇啹溴潏傸埇傖婘媆䙓喂䂷幋嬉滯䇞诙埡髕㔗