Re: Documenting serializable vs snapshot isolation levels
От | Simon Riggs |
---|---|
Тема | Re: Documenting serializable vs snapshot isolation levels |
Дата | |
Msg-id | 1230924017.4032.136.camel@ebony.2ndQuadrant обсуждение исходный текст |
Ответ на | Re: Documenting serializable vs snapshot isolation levels (Tom Lane <tgl@sss.pgh.pa.us>) |
Список | pgsql-hackers |
On Fri, 2009-01-02 at 13:47 -0500, Tom Lane wrote: > "Kevin Grittner" <Kevin.Grittner@wicourts.gov> writes: > >> What do you mean by referential integrity? I don't believe you can > >> construct a foreign key problem at any transaction isolation level. > > > I mean that if someone attempts to maintain referential integrity with > > SQL code, without using explicit locks, it is not reliable. > > Presumably the implementation of foreign keys in PostgreSQL takes this > > into account and blocks the kind of behavior shown below. This > > behavior would not occur with true serializable transactions. > > IIRC the RI code has to fudge the normal serializable-snapshot behavior > in order to guarantee no constraint violation --- it has to be aware of > concurrent changes that would otherwise be invisible to a serializable > transaction. ...just to add that this is exactly as required by SQL Standard, i.e. RI works in Read Committed mode even within a Serializable transaction. -- Simon Riggs www.2ndQuadrant.comPostgreSQL Training, Services and Support
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