▁potential ▁consist ency ▁trade offs ▁for ▁distributed ▁systems . ▁ ▁A ▁high ▁avail ability ▁requirement ▁implies ▁that ▁the ▁system ▁must ▁rep licate ▁data . ▁As ▁soon ▁as ▁a ▁distributed ▁system ▁rep licates ▁data , ▁a ▁trade off ▁between ▁consist ency ▁and ▁laten cy ▁ar ises . ▁ ▁The ▁P AC EL C ▁theorem ▁was ▁first ▁described ▁by ▁Daniel ▁J . ▁Ab adi ▁from ▁Y ale ▁University ▁in ▁ 2 0 1 0 ▁in ▁a ▁blog ▁post , ▁which ▁he ▁later ▁formal ized ▁in ▁a ▁paper ▁in ▁ 2 0 1 2 . ▁The ▁purpose ▁of ▁P AC EL C ▁is ▁to ▁address ▁his ▁th esis ▁that ▁" Ign oring ▁the ▁consist ency / l aten cy ▁trade off ▁of ▁rep licated ▁systems ▁is ▁a ▁major ▁o vers ight ▁[ in ▁C AP ], ▁as ▁it ▁is ▁present ▁at ▁all ▁times ▁during ▁system ▁operation , ▁whereas ▁C AP ▁is ▁only ▁relevant ▁in ▁the ▁arg u ably ▁rare ▁case ▁of ▁a ▁network ▁partition ." ▁ ▁Database ▁P AC EL C ▁ratings ▁▁ ▁Database ▁P AC EL C ▁ratings ▁are ▁from ▁▁▁ ▁The ▁default ▁versions ▁of ▁Dynam o DB , ▁Cass andra , ▁R iak ▁and ▁Cos mos ▁DB ▁are ▁PA / EL ▁systems : ▁if ▁a ▁partition ▁occurs , ▁they ▁give ▁up ▁consist ency ▁for ▁avail ability , ▁and ▁under ▁normal ▁operation ▁they ▁give ▁up ▁consist ency ▁for ▁lower ▁laten cy . ▁ ▁Ful ly ▁AC ID ▁systems ▁such ▁as ▁Vol t DB / H - Store , ▁Meg ast ore ▁and ▁MySQL ▁Cl uster