#coding:utf-8
#
# id:           bugs.core_4302
# title:         Lookup (or scan) in descending index could be very inefficient for some keys
# decription:   
#                  ### NB, 16-apr-2016  ###
#                  1. Bug of this ticket was introduced _after_ FB 3.0 Alpha1 release and was fixed 21-dec-2013.
#                     I could not reproduce poor statistics (too big value of fetches) on WI-T3.0.0.30566 (Alpha1 release),
#                     so temporary build was created based on snapshot of 20-dec-2013 (on POSIX): LI-T3.0.0.30800.
#                     This snapshot DOES reproduce problem: number of fetches for val=1 or val=3 is less than 30 
#                     while for val=2 produces number of fetches more than 210'000.
#                     For 2.5.x number of fetches is about 59...67, so common threshold was choosen to value 70.
#                  2. Test was refactored: querying to database 'mon-stat-gathering-N_M.fdb' was removed, all necessary
#                     output one may achieve by trivial view (v_mon) that queries mon$io_stats and and table (t_mon) that 
#                     serves as log.
#               
#                  Reproduced on LI-T3.0.0.30800 (snapshot on 20-dec-2013).
#                  Current results were checked on Windows (2.5.6.26994, 3.0.0.32484, 4.0.0.138) and POSIX (4.0.0.138)
#                
# tracker_id:   CORE-4302
# min_versions: ['2.5.3']
# versions:     2.5.3
# qmid:         None

import pytest
from firebird.qa import db_factory, isql_act, Action

# version: 2.5.3
# resources: None

substitutions_1 = []

init_script_1 = """"""

db_1 = db_factory(sql_dialect=3, init=init_script_1)

test_script_1 = """
     recreate table t_mon(rn smallint, pg_fetches bigint);

     recreate view v_mon as 
     select i.mon$page_fetches as pg_fetches
     from mon$attachments a
     left join mon$io_stats i on a.mon$stat_id=i.mon$stat_id     
     where a.mon$attachment_id = current_connection;

     recreate table t1 (id int, val int);
     commit;

     set term ^;
     execute block as
     declare i int = 0;
     begin
       while (i < 100000) do
       begin
         insert into t1 values (:i, mod(:i, 10));
         i = i + 1;
       end
     end
     ^
     set term ;^
     commit;

     create descending index t1_desc_idx on t1 (val);
     commit;

     set list on;
      
     insert into t_mon(rn, pg_fetches) values( 1, (select pg_fetches from v_mon));
     select * from t1 where val <= 1 order by val desc rows 1;
     commit;
     insert into t_mon(rn, pg_fetches) values( 2, (select pg_fetches from v_mon));
     commit;

     insert into t_mon(rn, pg_fetches) values( 3, (select pg_fetches from v_mon));
     select * from t1 where val <= 2 order by val desc rows 1;
     commit;
     insert into t_mon(rn, pg_fetches) values( 4, (select pg_fetches from v_mon));
     commit;
     
     insert into t_mon(rn, pg_fetches) values( 5, (select pg_fetches from v_mon));
     select * from t1 where val <= 3 order by val desc rows 1;
     commit;
     insert into t_mon(rn, pg_fetches) values( 6, (select pg_fetches from v_mon));
     commit;

     select 
          rn as measure
         ,iif( fetches_diff < max_allowed, 'OK, less then ', 'BAD: '|| fetches_diff ||' - greater then ')  || max_allowed as fetches_count
     from (
         select 
             rn
            ,fetches_at_end - fetches_at_beg as fetches_diff
            ,70 as max_allowed
         --  ^        ###################################################
         --  |        #                                                 #
         --  +------- #   T H R E S H O L D     F O R    F E T C H E S  #
         --           #                                                 #
         --           ###################################################
         from (
           select rn, max(iif(bg=1, pg_fetches, null)) as fetches_at_beg, max(iif(bg=1, null, pg_fetches)) as fetches_at_end
           from (
               select 1+(rn-1)/2 as rn, mod(rn,2) as bg, pg_fetches 
               from t_mon
           )
           group by rn
         )
     )
     order by measure;
  """

act_1 = isql_act('db_1', test_script_1, substitutions=substitutions_1)

expected_stdout_1 = """
    ID                              1
    VAL                             1
    ID                              2
    VAL                             2
    ID                              3
    VAL                             3

    MEASURE                         1
    FETCHES_COUNT                   OK, less then 70

    MEASURE                         2
    FETCHES_COUNT                   OK, less then 70

    MEASURE                         3
    FETCHES_COUNT                   OK, less then 70

  """

@pytest.mark.version('>=2.5.3')
def test_1(act_1: Action):
    act_1.expected_stdout = expected_stdout_1
    act_1.execute()
    assert act_1.clean_expected_stdout == act_1.clean_stdout