C:\1Install\fb30>isql 192.168.0.201/3330:empty30 -user sysdba -pas masterke -n
Database:  192.168.0.201/3330:empty30, User: sysdba
SQL> out nul; select count(*) from tmp;
SQL> set plan on; set stat on;
SQL> select a.f1, a.cnt_max from (select a.f1, count(*) cnt_max from tmp a group by a.f1) a
CON> join (select distinct cnt
CON>         from (select count(*) cnt from tmp x group by x.f1)
CON>        order by cnt desc rows 2) x
CON> on a.cnt_max = x.cnt;

PLAN HASH (SORT (X X ORDER TMP_F1), A A ORDER TMP_F1)
Current memory = 304264576
Delta memory = 14620920
Max memory = 304936248
Elapsed time=  6643.75 sec 
Buffers = 65000
Reads = 10663599
Writes 460
Fetches = 49437024
SQL> set stat off;
.................................
6643597 ms, 10659719 read(s), 49365119 fetch(es)

Table                             Natural     Index
****************************************************
TMP                                        20000002

SQL> select cast('now' as timestamp) t0 from rdb$database;

T0                              2013-08-12 17:22:35.6040


SQL> set stat on;
SQL> set term ^;
SQL> execute block as
CON>   declare n int = 10000000;
CON>   declare v_att int;
CON>   declare v_trn int;
CON> begin
CON>   while (n>0) do begin
CON>     v_att=current_connection;
CON>     v_trn=current_transaction;
CON>     n=n-1;
CON>   end
CON> end^
Current memory = 311518264
Delta memory = 9528
Max memory = 313634856
Elapsed time= 3.47 sec
Buffers = 65000
Reads = 0
Writes 0
Fetches = 0
SQL> set term ;^
SQL> set stat off;
SQL> rollback;
SQL> set echo off;
SQL> select cast('now' as timestamp) t1 from rdb$database;

T1                              2013-08-12 17:22:39.1090

SQL> select cast('now' as timestamp) t0 from rdb$database;

T0                              2013-08-12 17:35:00.3590


SQL> set stat on;
SQL> set term ^;
SQL> execute block as
CON>   declare n int = 10000000;
CON>   declare v_att int;
CON>   declare v_trn int;
CON>   declare x_att int;
CON>   declare x_trn int;
CON> begin
CON>   v_att=current_connection;
CON>   v_trn=current_transaction;
CON>   while (n>0) do begin
CON>     select mon$attachment_id, mon$transaction_id
CON>     from mon$transactions
CON>     where mon$attachment_id = :v_att and mon$transaction_id = :v_trn
CON>     into x_att, x_trn;
CON>     n=n-1;
CON>   end
CON> end^
Current memory = 311545968
Delta memory = 85440
Max memory = 313634856
Elapsed time= 22.74 sec
Buffers = 65000
Reads = 0
Writes 0
Fetches = 1
SQL> set term ;^
SQL> set stat off;
SQL> rollback;
SQL> set echo off;
SQL> select cast('now' as timestamp) t1 from rdb$database;

T1                              2013-08-12 17:35:23.1180