時(shí)間：2015-06-28 00:00:00 來源：IT貓撲網(wǎng) 作者：網(wǎng)管聯(lián)盟 我要評(píng)論(2)
recursive calls: Oracle自己偷偷執(zhí)行的，不去關(guān)注
db block gets: current read,直接讀buffer
consistent gets: consistent read，讀rollback segment中Undo后讀
physical reads:read from disk
因?yàn)閘ogical reads=current reads+consistent reads=physical reads+ non-phisical reads
所以hit ratio= 1-physical reads/logical reads=1- physical reads(consistent gets+current reads)
---------------------------------------------------------------------------------------------------------------------
以下是網(wǎng)上摘來的文檔，注意紅色的那段我認(rèn)為是描述不正確的，current read不是相對(duì)buffer而言，二是相對(duì)consistent read而言
· Recursive Calls. Number of recursive calls generated at both the user and system level.
Oracle Database maintains tables used for internal processing. When it needs to change these tables, Oracle Database generates an internal SQL statement, which in turn generates a recursive call.
In short, recursive calls are basically SQL performed on behalf of your SQL. So, if you had to parse the query, for example, you might have had to run some other queries to get data dictionary information. These would be recursive calls. Space management, security checks, calling PL/SQL from SQL—all incur recursive SQL calls.
· DB Block Gets. Number of times a CURRENT block was requested.
Current mode blocks are retrieved as they exist right now, not in a consistent read fashion.
Normally, blocks retrieved for a query are retrieved as they existed when the query began. Current mode blocks are retrieved as they exist right now, not from a previous point in time.
During a SELECT, you might see current mode retrievals due to reading the data dictionary to find the extent information for a table to do a full scan (because you need the "right now" information, not the consistent read). During a modification, you will access the blocks in current mode in order to write to them.
(DB Block Gets:請(qǐng)求的數(shù)據(jù)塊在buffer能滿足的個(gè)數(shù))
· Consistent Gets. Number of times a consistent read was requested for a block.
This is how many blocks you processed in "consistent read" mode. This will include counts of blocks read from the rollback segment in order to roll back a block.
This is the mode you read blocks in with a SELECT, for example.
Also, when you do a searched UPDATE/DELETE, you read the blocks in consistent read mode and then get the block in current mode to actually do the modification.
(Consistent Gets:數(shù)據(jù)請(qǐng)求總數(shù)在回滾段Buffer中)
· Physical Reads. Total number of data blocks read from disk. This number equals the value of "physical reads direct" plus all reads into buffer cache. (Physical Reads:實(shí)例啟動(dòng)后，從磁盤讀到Buffer Cache數(shù)據(jù)塊數(shù)量)
· Sorts (disk). Number of sort operations that required at least one disk write. Sorts that require I/O to disk are quite resource intensive. Try increasing the size of the initialization parameter SORT_AREA_SIZE.
關(guān)鍵詞標(biāo)簽：Oracle
相關(guān)閱讀
熱門文章
Oracle中使用alter table來增加,刪除,修改列的語法
oracle中使用SQL語句修改字段類型-oracle修改SQL語句案例
誤刪Oracle數(shù)據(jù)庫實(shí)例的控制文件
為UNIX服務(wù)器設(shè)置Oracle全文檢索
人氣排行 oracle中使用SQL語句修改字段類型-oracle修改SQL語句案例 Oracle中使用alter table來增加,刪除,修改列的語法 ORACLE SQL 判斷字符串是否為數(shù)字的語句 ORACLE和SQL語法區(qū)別歸納(1) oracle grant 授權(quán)語句 ORACLE修改IP地址后如何能夠使用 如何加速Oracle大批量數(shù)據(jù)處理 Oracle刪除表的幾種方法