oracle培訓(xùn)講義(編輯修改稿)
2025-05-13 12:33 本頁面
【文章內(nèi)容簡介】 sorts (memory) 0 sorts (disk) 6219 rows processedSQL show arraysizearraysize 15SQL set arraysize 2SQL select *from t。已選擇6219行。Statistics 0 recursive calls 0 db block gets 3156 consistent gets 0 physical reads 0 redo size 683239 bytes sent via SQL*Net to client 34702 bytes received via SQL*Net from client 3111 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6219 rows processedSQL set arraysize 4SQL /已選擇6219行。Statistics 0 recursive calls 0 db block gets 1618 consistent gets 0 physical reads 0 redo size 495111 bytes sent via SQL*Net to client 17597 bytes received via SQL*Net from client 1556 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6219 rows processedSQL set arraysize 8SQL /已選擇6219行。Statistics 0 recursive calls 0 db block gets 853 consistent gets 0 physical reads 0 redo size 401094 bytes sent via SQL*Net to client 9050 bytes received via SQL*Net from client 779 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6219 rows processedSQL set arraysize 16SQL /已選擇6219行。Statistics 0 recursive calls 0 db block gets 465 consistent gets 0 physical reads 0 redo size 354025 bytes sent via SQL*Net to client 4771 bytes received via SQL*Net from client 390 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 6219 rows processed252。 phisical reads：指Oracle把數(shù)據(jù)從硬盤讀到內(nèi)存的次數(shù)，也就是讀取到內(nèi)存的數(shù)據(jù)塊數(shù)，然后我們執(zhí)行邏輯I/O從內(nèi)存讀取數(shù)據(jù)，因此，一般情況下，物理I/O都跟隨著邏輯I/O。phisical reads分為兩種：reading data in from datafiles：對數(shù)據(jù)文件讀取獲得索引數(shù)據(jù)或者表數(shù)據(jù)，這種I/O立刻跟隨著邏輯I/O。direct reads from temp：當sort area或hash area不能在內(nèi)存中容納sort data或hash data時，Oracle會把部分數(shù)據(jù)交換到temp表空間，然后再讀取，這種讀取會越過buffer cache，不會引發(fā)邏輯I/O。第一種物理I/O，我們不能避免，如果在第一次查詢后，同樣的查詢還需要物理I/O,，則可能是因為data buffer cache太小，在物理內(nèi)存足夠的情況下，可以把data buffer cache增大。對于第二種，我們可以通過設(shè)置合適的sort_area_size和hash_area_size大小，來降低phisical reads，注意，在Oracle9i中，要先把workarea_size_policy參數(shù)設(shè)置為manual，改動sort_area_size及hash_area_size參數(shù)才會生效，8i可以直接設(shè)置sort_area_size。SQL conn scott/tiger@catalog已連接。SQL show parameter workNAME TYPE VALUE workarea_size_policy string AUTOSQL alter session set workarea_size_policy=manual。會話已更改。SQL alter session set sort_area_size=0。會話已更改。SQL set autotrace traceonly statisticsSQL select * from t order by object_id。已選擇6219行。Statistics 0 recursive calls 24 db block gets 80 consistent g
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