On Mon, 03 Sep 2012 10:09:12 -0000, "Fabiano"
<fabiano@...>
wrote:

> Hi all,
>
> create domain d1 varchar(100) character set utf8;
> create table t1 (c1 d1, c2 d1);
> alter table t1 add unique (c1, c2);
>
> create domain d2 varchar(100) character set utf8 collate unicode_ci_ai;
> create table t2 (c1 d2, c2 d2);
> alter table t2 add unique (c1, c2);
> -- unsuccessful metadata update. key size exceeds implementation
> restriction for index "RDB$2".
>
> Is this error expected?
>
> Firebird 2.5, database page size 4096.

As far as I know collations add additional information to each key,
increasing the length. The maximum length of a key is +/- 1/4 of the page
size (assuming a single key). For a normal UTF8 collation that would be 253
bytes (see
http://www.firebirdsql.org/refdocs/langrefupd25-ddl-index.html#langrefupd25-tbl-max-indexable-strlen
). So in the normal UTF8 case your key is > 200 characters. Her I also
assume there is some additional overhead as it is a compound index.

I don't know the exact size increase for a collation (and I suspect it
depends on the collation), but I guess this pushes it beyond the limit of
1015 bytes allowed per key. The simplest solution is to move to a greater
page size. Another option of course is to check if you really need
VARCHAR(100) for these columns.

Mark