От: kenneth d'souza
Тема: Locks and Waiters
Дата: ,
Msg-id: BAY116-F256006D270E22F9D1062E0ED060@phx.gbl
(см: обсуждение, исходный текст)
Список: pgsql-docs

<div style="background-color:"><div class="RTE">I have question on Locks and waiting. </div><p>In the readme
pgsql/src/backend/storage/lmgr/README<p> <div></div><div></div><div></div>Each waiter is awoken if (a) its request
<div></div>doesnot conflict with already-granted locks, and (b) its request does <div></div>not conflict with the
requestsof prior un-wakable waiters. <div></div><div></div>Let us imagine if there is Process P which is holding a lock
andthere are individual waiters p1 p2 p3 p4 p5 p6 requiring the same lock. Now since they are in conflict it is sure
thatthere will be wait queue that will get generated as in p1 p2 p3 p4 p5 p6. <div></div>Image if Process P releases it
lock.As per explaination given in (a) it is sure that p1 will wake up. What is the status of p2. It was in conflict
withprocess P and hence should we term it that it will not wake up. Same is the case with p2 ... p6. <div></div>Under
whatcircumstance will p2 be also woken up taking into consideration that the lock held by process P is released.
<div></div>Secondlyif p2 is not woken up and if p3's lock doesn't conflict with P and p2 then by rule(b) will p3 move
ahead  ofp2 <div></div><div></div>Thanks, <div></div>Kenneth <div></div><div></div></div><br clear="all" /><hr />Tried
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