XID Data Types

On Mon, 03 May 2004 13:38:45 -0400, Ericson Smith <eric@did-it.com>
wrote:

didit=# select *,xmin from settings where xmin > '187167023'::xid limit 5;
ERROR: operator does not exist: xid > xid

There might be better solutions, but when I ran into the same problem,
the age(xid) function helped at lot.

I've been reading about the CREATE OPERATOR command.

Apparently there is an operator to test equality between an xmin type
and an integer type, how do it go about creating another type to make a

or < comparison ?

The documents are pretty straightforward about creating other types, but
I was not able to find much information about the xid type. In pg_proc,
I found that there are the following comparators:

xideqint4
xideq

Which would make a equal comparison between an xid = int4, or xid=xid.
This seems to work ok. My goal is to find a decent way of syncing
records with an external cache. The xmin field that exists within every
table is updated whenever a transaction is successful on record(s). I
have a process that will run, and look at the last xmin value (I stored
in another table), and grab records that have an xmin greater than the
last stored value. We think that this is a better way to sync data than
the old way of using triggers that updated a sync table on inserts and
deletes. Only certain tables need to be sync'd with our external caches.

Any suggestions if this is the right way to go, or is there another way
that this particular problem could be solved?

Any suggestions would be really appreciated.

Regards
- Ericson Smith

Manfred Koizar wrote:

Manfred Koizar wrote:

On Mon, 03 May 2004 13:38:45 -0400, Ericson Smith <eric@did-it.com>
wrote:

didit=# select *,xmin from settings where xmin > '187167023'::xid limit 5;
ERROR: operator does not exist: xid > xid

There might be better solutions, but when I ran into the same problem,
the age(xid) function helped at lot.

Slony contains an xxid data type that follows exactly the xid semantics.
It comes with a full operator class so that you can even put indexes on
xxid type columns. Shouldn't be too hard to define those operators for
the builtin xid type instead.

Jan

--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck@Yahoo.com #

Jan Wieck wrote:

Manfred Koizar wrote:

On Mon, 03 May 2004 13:38:45 -0400, Ericson Smith <eric@did-it.com>
wrote:

didit=# select *,xmin from settings where xmin > '187167023'::xid limit 5;
ERROR: operator does not exist: xid > xid

There might be better solutions, but when I ran into the same problem,
the age(xid) function helped at lot.

Slony contains an xxid data type that follows exactly the xid semantics.
It comes with a full operator class so that you can even put indexes on
xxid type columns. Shouldn't be too hard to define those operators for
the builtin xid type instead.

Should we just get that into our CVS so Slony doesn't have to distribute
its own?

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073

Bruce Momjian wrote:

Jan Wieck wrote:

Manfred Koizar wrote:

On Mon, 03 May 2004 13:38:45 -0400, Ericson Smith <eric@did-it.com>
wrote:

didit=# select *,xmin from settings where xmin > '187167023'::xid limit 5;
ERROR: operator does not exist: xid > xid

There might be better solutions, but when I ran into the same problem,
the age(xid) function helped at lot.

Slony contains an xxid data type that follows exactly the xid semantics.
It comes with a full operator class so that you can even put indexes on
xxid type columns. Shouldn't be too hard to define those operators for
the builtin xid type instead.

Should we just get that into our CVS so Slony doesn't have to distribute
its own?

It has to anyway, at least as long as it is supposed to be a version
upgrade aid that supports replicating from 7.3.x or 7.4.x to a newer
version so that the upgrade downtime reduces to a few seconds for a
master->slave switchover.

Jan

--
#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#================================================== JanWieck@Yahoo.com #

Jan Wieck <JanWieck@Yahoo.com> writes:

Bruce Momjian wrote:

Should we just get that into our CVS so Slony doesn't have to distribute
its own?

It has to anyway, at least as long as it is supposed to be a version
upgrade aid that supports replicating from 7.3.x or 7.4.x

No doubt ... but I agree that we *should* push full comparison support
for type XID into CVS.

regards, tom lane

Tom Lane wrote:

Jan Wieck <JanWieck@Yahoo.com> writes:

Bruce Momjian wrote:

Should we just get that into our CVS so Slony doesn't have to distribute
its own?

It has to anyway, at least as long as it is supposed to be a version
upgrade aid that supports replicating from 7.3.x or 7.4.x

No doubt ... but I agree that we *should* push full comparison support
for type XID into CVS.

Yes, let's at least match it so we can have testing of the code in both
places, and prevent the need to load them in if the version is new
enough.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073