执行计划和统计信息的含义?
我执行语句
select * from tsum_data_w
生成的执行计划和统计信息如下:
Execution Plan
----------------------------------------------------------
0 SELECT STATEMENT Optimizer=CHOOSE (Cost=450 Card=2 Bytes=230
00000)
1 0 COUNT (STOPKEY)
2 1 TABLE ACCESS (FULL) OF 'TSUM_DATA_W' (Cost=450 Card=1000
000 Bytes=23000000)
Statistics
----------------------------------------------------------
0 recursive calls
0 db block gets
4673 consistent gets
4663 physical reads
0 redo size
719 bytes sent via SQL*Net to client
503 bytes received via SQL*Net from client
4 SQL*Net roundtrips to/from client
0 sorts (memory)
0 sorts (disk)
2 rows processed
请问:
(1)括号内的Cost=450 Card=1000
000 Bytes=23000000分别是什么意思?
(2)
0 db block gets
4673 consistent gets
4663 physical reads
又是什么意思呢?
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