(Straying a bit from the OP, but this is fun, no? And anyway, I rather expect this may be interesting/useful for him too).

An alternative (in postgresql) would be to use regex-index, which can be used when the submitted search-string or regex is anchored:

select count(*) from azjunk6; -- 1 million rows random data:
  count  
---------
 1000000
(1 row)

-- without index:
 select * from azjunk6 where txt ~ '^car[sz]';

                                      txt                             
+           
----------------------------------------------------------------------
+------------
 carsxbutsvamedynximrftmimgtzirtuorik lunamb qpjvwmixlxpmcu  mm  rzotj
+jnfxr syfrj
 carzfhndjznvpgcpwqb fp bqpljspqqpzfbbswefzs pjoocqztqkjxyvbr qalcfzme
+bezz ftmyi 
 carziicmi zzzvt beqsupgdwkhdg luvvmhhay bj b r soaiyfftiqgq hs brdzaf
+dztmtvfvrdn
 carziogaizohcqcphs ksucyeod q yvfallob  pctvmwplm igzsqalyy dqsjpiikx
+wyyxesenbeq
 carzw rcfwlqcweao jzeyxkchgc g vyvujtbsbeiewj inuelmldsa mpjevzmo  pc
+pwi  kfajug
 carzxrk qyk palimcwokbw hbdcsmxehcsnrop prrokygyi ssngegzksrzvged cu 
+oxr yozt ca
(6 rows)

Time: 1147.420 ms

-- now make a text_pattern_ops index:

 create index azjunk6_text_pattern_ops_idx on azjunk6 (txt text_patter
+n_ops);
 Time: 7282.579 ms

-- with index:
 select * from azjunk6 where txt ~ '^car[sz]';

                                      txt                             
+           
----------------------------------------------------------------------
+------------
 carsxbutsvamedynximrftmimgtzirtuorik lunamb qpjvwmixlxpmcu  mm  rzotj
+jnfxr syfrj
 carzfhndjznvpgcpwqb fp bqpljspqqpzfbbswefzs pjoocqztqkjxyvbr qalcfzme
+bezz ftmyi 
 carziicmi zzzvt beqsupgdwkhdg luvvmhhay bj b r soaiyfftiqgq hs brdzaf
+dztmtvfvrdn
 carziogaizohcqcphs ksucyeod q yvfallob  pctvmwplm igzsqalyy dqsjpiikx
+wyyxesenbeq
 carzw rcfwlqcweao jzeyxkchgc g vyvujtbsbeiewj inuelmldsa mpjevzmo  pc
+pwi  kfajug
 carzxrk qyk palimcwokbw hbdcsmxehcsnrop prrokygyi ssngegzksrzvged cu 
+oxr yozt ca
(6 rows)

Time: 12.524 ms  -->  100x faster
[download]

(It can be handy to have both a 'normal' btree index *and* such a text_pattern_ops regex index.)

See also: PostgreSQL index opclasses

You can get another interesting indextype from pg_trgm, a postgresql extension. This will give you not indexed regexen but indexed trigrams: PostgreSQL pg_trgm extension. (disadvantage: large index-size)

And FWIW: in 9.2devel, there is work ongoing to make it possible to combine the two: regexed trigram indexes...