Re: Getting "could not read block" error when creating an index on a function.

Thank you for the responses! I was going to go with a materialized view, but then realized that since the dataset is
staticit’s really no different from just creating a new table and indexing that. The suggestions provide useful advice
forthe future though. 

Cheers,
Demitri

> On Dec 30, 2020, at 3:14 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
>> Am Wed, Dec 30, 2020 at 02:37:59PM -0500 schrieb Demitri Muna:
>>> I want to index the results of these repeated, unchanging calculations to speed up other queries. Which mechanism
wouldbe best to do this? Create additional columns? Create another table? 
>
>> A materialized view ?
>
> Yeah, or you might be able to do something with a before-insert-or-update
> trigger that computes whatever desired value you want and fills it into a
> derived column.  Indexing that column then gives the same results as
> indexing the derived expression; but it sidesteps the semantic problems
> because the time of computation of the expression is well-defined, even
> if it's not immutable.
>
> You might try to avoid a handwritten trigger by defining a generated
> column instead, but we insist that generation expressions be immutable
> so it won't really work.  (Of course, you could still lie about the
> mutability of the expression, but I can't recommend that.  Per Henry
> Spencer's well-known dictum, "If you lie to the compiler, it will get its
> revenge".  He was speaking of C compilers, I suppose, but the principle
> applies to database query optimizers too.)
>
>             regards, tom lane