BLERe: AW: AW: [HACKERS] relation ### modified while in use

[Hiroshi Inoue]

Zeugswetter Andreas SB wrote: > > > > What I'm proposing is that once an xact has touched a > > > > table, other xacts should not be able to apply schema updates to that > > > > table until the first xact commits. > > > > > > No, this would mean too many locks, and would leave the dba with hardly a > > > chance to alter a table. > > > > > > > Are there many applications which have many SELECT statements(without > > FOR UPDATE) in one tx ? > > Why not ? > It seems to me that multiple SELECT statements in a tx has little meaning unless the tx is executed in SERIALIZABLE isolation level. > > > As for locks,weak locks doesn't pass intensive locks. Dba > > seems to be able to alter a table at any time. > > Sorry, I don't understand this sentence. Tom suggested placing a shared lock on > any table that is accessed until end of tx. Noone can alter table until all users >have > closed their txns and not accessed tables again. Remember that this would include > creating an index ... > What I meant is the following though I may be misunderstanding your point. Session-1. # begin; # declare myc cursor for select * from t1; Session-2. # begin; # lock table t1; [blocked] Session-3. # begin; # select * from t1; [blocked] Session-1. # abort; Then Session-2. LOCK TABLE # but Session-3. [still blocked] Regards. Hiroshi Inoue