Example for Full-Text Search Index doesn't work

[Christophe Pettus]

The example given for creating an index on a to_tsvector() call doesn't actually work, since to_tsvector() is not immutable (the results of it can change with changes to the underlying dictionaries it is ruled it is built on).

xof=# create table t (z text);
CREATE TABLE
xof=# create index on t(to_tsvector(z));
ERROR:  functions in index expression must be marked IMMUTABLE

(As a note, indexes on tsvectors should be GIN indexes rather than B-tree.)

For documentation purposes in the release notes, I'd suggest pointing the reader to the PostgreSQL documentation that describes how to handle this situation.