Bruce Momjian <br...@momjian.us> writes:
> On Fri, Mar 9, 2012 at 04:36:08PM -0800, David E. Wheeler wrote:
>> A <type>bigint</type> key is displayed with its
>> high-order half in the <structfield>classid</> column, its low-order
>> half
>> in the <structfield>objid</> column, and <structfield>objsubid</> equal
>> ! to 1. The original <type>bigint</type> value can be reassembled with the
>> ! expression <literal>(classid::int::bit(64) << 32 |
>> ! objid::int::bit(64))::bigint</literal>. Integer keys are displayed with
>> the
>> ! first key in the
>> <structfield>classid</> column, the second key in the
>> <structfield>objid</>
>> column, and <structfield>objsubid</> equal to 2. The actual meaning of
>> the keys is up to the user. Advisory locks are local to each database,
> Thanks, applied.
This formula is not actually correct, as you'd soon find out if you
experimented with values with the high-order bit of the low-order word
set. (Hint: sign extension.)
The correct formula is both simpler and far more efficient:
(classid::int8 << 32) | objid::int8
This works because oidtoi8 correctly treats the OID value as unsigned.
regards, tom lane
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