Slow query after upgrade from 9.0 to 9.2

Hi!

Small query run on 9.0 very fast:

SELECT * from sygma_arrear sar where sar.arrear_import_id = (
select sa.arrear_import_id from sygma_arrear sa, arrear_import ai
where sa.arrear_flag_id = 2
AND sa.arrear_import_id = ai.id
AND ai.import_type_id = 1
order by report_date desc limit 1)
AND sar.arrear_flag_id = 2
AND sar.credit_id = 3102309

"Index Scan using sygma_arrear_credit_id on sygma_arrear sar
(cost=0.66..362.03 rows=1 width=265)"
" Index Cond: (credit_id = 3102309)"
" Filter: ((arrear_import_id = $0) AND (arrear_flag_id = 2))"
" InitPlan 1 (returns $0)"
" -> Limit (cost=0.00..0.66 rows=1 width=8)"
" -> Nested Loop (cost=0.00..3270923.14 rows=4930923 width=8)"
" -> Index Scan Backward using report_date_bank_id_key
on arrear_import ai (cost=0.00..936.87 rows=444 width=8)"
" Filter: (import_type_id = 1)"
*" -> Index Scan using sygma_arrear_arrear_import_id_idx
on sygma_arrear sa (cost=0.00..6971.15 rows=31495 width=4)"**
**" Index Cond: (sa.arrear_import_id = ai.id)"**
**" Filter: (sa.arrear_flag_id = 2)"**
*
Engine uses index - great.

On 9.2

"Index Scan using sygma_arrear_credit_id on sygma_arrear sar
(cost=11.05..381.12 rows=1 width=265)"
" Index Cond: (credit_id = 3102309)"
" Filter: ((arrear_import_id = $0) AND (arrear_flag_id = 2))"
" InitPlan 1 (returns $0)"
" -> Limit (cost=0.00..11.05 rows=1 width=8)"
" -> Nested Loop (cost=0.00..54731485.84 rows=4953899 width=8)"
" Join Filter: (sa.arrear_import_id = ai.id)"
" -> Index Scan Backward using report_date_bank_id_key
on arrear_import ai (cost=0.00..62.81 rows=469 width=8)"
" Filter: (import_type_id = 1)"
*" -> Materialize (cost=0.00..447641.42 rows=6126357
width=4)"**
**" -> Seq Scan on sygma_arrear sa
(cost=0.00..393077.64 rows=6126357 width=4)"**
**" Filter: (arrear_flag_id = 2)"**
*
Seq scan... slooow.

Why that's happens? All configurations are identical. Only engine is
different.

When I make index on to column: (arrear_import_id,arrear_flag_id) then
engine use it and run fast.

--
Andrzej Zawadzki