Re: SSI freezing bug

On 2013-09-20 13:53:04 +0200, Andres Freund wrote:
> Hi,
> 
> 
> On 2013-09-20 13:55:36 +0300, Heikki Linnakangas wrote:
> > When a tuple is predicate-locked, the key of the lock is ctid+xmin. However,
> > when a tuple is frozen, its xmin is changed to FrozenXid. That effectively
> > invalidates any predicate lock on the tuple, as checking for a lock on the
> > same tuple later won't find it as the xmin is different.
> > 
> > Attached is an isolationtester spec to demonstrate this.
> 
> Do you have any idea to fix that besides keeping the xmin horizon below the
> lowest of the xids that are predicate locked? Which seems nasty to
> compute and is probably not trivial to fit into the procarray.c
> machinery?

A better solution probably is to promote tuple-level locks if they exist
to a relation level one upon freezing I guess?

Greetings,

Andres Freund

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