Thread: Difference between 7.2 and 7.3, possible bug?

create table test (col_a bigint);
update test set col_a = nullif('200', -1);

The above works fine on 7.2 but the update fails on 7.3b2 with the
following error:

ERROR:  column "col_a" is of type bigint but expression is of type text
    You will need to rewrite or cast the expression

Is this change in behavior intentional or is it a bug?


This situation is occuring because of two changes.  The first being the
difference in how the server is handling the above update in 7.2 vs.
7.3.  The second is a change in the jdbc driver in 7.3.  The actual
update in jdbc looks like:
update test set col_a = nullif(?, -1);
and a "setLong(1, 200)" call is being done.  In 7.2 the jdbc driver
bound the long/bigint value as a plain number, but in 7.3 it binds it
with quotes making it type text and exposing the change in server
behavior.  This change was made in the jdbc driver to work around the
fact that indexes are not used for int2 or int8 columns unless the value
is enclosed in quotes (or an explicit cast is used).  I am not sure if
the recent changes for implicit casts fixes this index usage problem in
the server or not.

So I have three options here:

1) if this is a server bug wait for a fix for 7.3
2) revert the jdbc driver back to not quoting int2 and int8 values
      - If the server now handles using indexes on int2/int8 columns then
        this should be done anyway
      - It the server still has problems with using indexes without the
        quotes then this removes an often requested bugfix/workaround
        for the index usage problem
3) Just have people rework their sql to avoid the change in behavior

Any suggestions?


thanks,
--Barry

Barry Lind <barry@xythos.com> writes:
> create table test (col_a bigint);
> update test set col_a = nullif('200', -1);
> The above works fine on 7.2 but the update fails on 7.3b2 with the
> following error:
> ERROR:  column "col_a" is of type bigint but expression is of type text
>     You will need to rewrite or cast the expression

> Is this change in behavior intentional or is it a bug?

This is an intentional tightening of implicit-cast behavior.

> This situation is occuring because of two changes.  The first being the
> difference in how the server is handling the above update in 7.2 vs.
> 7.3.  The second is a change in the jdbc driver in 7.3.  The actual
> update in jdbc looks like:
> update test set col_a = nullif(?, -1);
> and a "setLong(1, 200)" call is being done.  In 7.2 the jdbc driver
> bound the long/bigint value as a plain number, but in 7.3 it binds it
> with quotes making it type text and exposing the change in server
> behavior.

I would say that that is a very bad decision in the JDBC driver and
should be reverted ... especially if the driver is not bright enough
to notice the context in which the parameter is being used.  Consider
for example

regression=# select 12 + 34;
 ?column?
----------
       46
(1 row)

regression=# select '12' + '34';
 ?column?
----------
 d
(1 row)

Not exactly the expected result ...

> 2) revert the jdbc driver back to not quoting int2 and int8 values
>       - If the server now handles using indexes on int2/int8 columns then
>         this should be done anyway
>       - It the server still has problems with using indexes without the
>         quotes then this removes an often requested bugfix/workaround
>         for the index usage problem

You are trying to mask a server problem in the driver.  This is not a
good idea.  The server problem is short-term (yes, we've finally agreed
how to fix it, and it will happen in 7.4), but a client-library hack to
mask it will cause problems indefinitely.

            regards, tom lane

Tom Lane wrote:
> I would say that that is a very bad decision in the JDBC driver and
> should be reverted ... especially if the driver is not bright enough
> to notice the context in which the parameter is being used.  Consider
> for example
...
>
> You are trying to mask a server problem in the driver.  This is not a
> good idea.  The server problem is short-term (yes, we've finally agreed
> how to fix it, and it will happen in 7.4), but a client-library hack to
> mask it will cause problems indefinitely.
>
>             regards, tom lane
>

Tom,

Thanks for the quick reply.  I will back out the jdbc change.  It was
one of those changes I did reluctantly.  I have been pushing back for a
couple of releases now saying that this is a server bug and needs to be
fixed there.  But it didn't seem like that was ever going to happen so I
finally gave in.  For some users this bug of not using indexes for
int2/int8 makes it impossible for them to use postgres.  This happens
for users who are using a database abstraction layer that doesn't allow
the user to actually touch the sql being sent to the server.  Therefore
they have no opportunity to work around the underlying bug and can't use
postgres as their database because of the performance problems.

I am glad to here this is finally getting resolved for 7.4.

thanks,
--Barry