Thread: age(xid) function bug
I see we recommend using the age(xid) function to check for XID wraparound: http://www.postgresql.org/docs/8.3/static/routine-vacuuming.html#VACUUM-FOR-WRAPAROUND However, the function only does a subtraction with no adjustment for overflow, and considering it returns a signed int, it can't even display the full range of valid values: test=> \df age List of functions Schema | Name | Result data type | Argument data types------------+------+------------------+----------------------------------------------------------...pg_catalog | age | integer | xid For example: test=> select txid_current(); txid_current-------------- 397(1 row)test=> select age('10000'::xid); age--------9602(1 row) Seems this is a bug. I think the fix is to do the arithmetic in int8 and return an int8. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
Bruce Momjian <bruce@momjian.us> writes: > However, the function only does a subtraction with no adjustment for > overflow, and considering it returns a signed int, it can't even display > the full range of valid values: Say again? The possible range of ages is only 2 billion. regards, tom lane
Tom Lane wrote: > Bruce Momjian <bruce@momjian.us> writes: > > However, the function only does a subtraction with no adjustment for > > overflow, and considering it returns a signed int, it can't even display > > the full range of valid values: > > Say again? The possible range of ages is only 2 billion. If we assume that only xid stored in actual tables are used, yes: test=> select txid_current(); txid_current-------------- 402(1 row)test=> select age('4294967290'::xid); age-----409(1 row) OK, so it does work based on the limitations we place on stored xids. -- Bruce Momjian <bruce@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + If your life is a hard drive, Christ can be your backup. +