Hi Ben,
If the below idea of allowing NULL values for Indexed columns makes
sense., shall we add an attribute (allow_null_index = false kind) as an
optional parameter for such type of columns and ensure compatibility with
existing/old schema? Does it sound okay?
Thanks
Krishna Mohan
-----Original Message-----
From: Ben Pfaff [mailto:b...@ovn.org]
Sent: Monday, April 11, 2016 11:00 AM
To: Ansari, Shad <shad.ans...@hpe.com>
Cc: Elluru, Krishna Mohan <elluru.kri.mo...@hpe.com>; dev@openvswitch.org
Subject: Re: [ovs-dev] [PATCH] ovsdb: Force columns that contain weak
references to be immutable.
On Mon, Apr 04, 2016 at 10:38:40PM +0000, Ansari, Shad wrote:
> >
> > HI Ben,
> > How does column which is weak reference and also configured as an
> > Index? If it is mutable, and the corresponding UUID going
> > away(deletion of record) leaves column value as NULL right? And what
> > would be the behavior if the table is a Root table also?
> > I am listing down, my assumptions:
> >
> > 1. In table X, If the column is index and a weak reference to table
> > y, on table y row deletion, the index field would become NULL and
> > since it is an index, constraint violation would occur and to avoid,
> > it is expected to remove the row first in table X and table Y row
> > deletion can happen in same txn or consequent transactions. Correct?
> > 2. If the table X is also a root table, and one of its column is an
> > index and weak reference to table Y, on row deletion in table Y,
> > constraint violation would occur, hence similar to above table X row
> > cleanup is expected to happen prior to table Y row deletion.
> >
> > If above 2 statements is true, index with weak reference is
> > becoming equivalent to strong reference. Am I correct?
> >
> > Thanks
> > Krishna Mohan
>
> Would it make sense to allow NULL values for columns that are references and
> indexes. Something like what MySQL allows for unique keys.
>
> http://dev.mysql.com/doc/refman/5.0/en/create-index.html
That's a reasonable idea. It could theoretically break some currently working
use cases, if someone has an OVSDB schema that relies on an index to ensure the
uniqueness of an empty column. I don't know whether there are schemas out
there that rely on this property.
I don't know how this idea would extend to multi-column indexes.
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