Oracle Enqueues Wait Events 一

    Oracle Enqueue Names

Enquences 是為了管理 連續訪問資料庫資源而設計的一種共享記憶體結構也叫鎖。它們可以與會話或事務相關聯。Enquences 名顯示在DBA_LOCK和DBA_LOCK_INTERNAL資料字典檢視的LOCK_TYPE列中。

資源被唯一地標識一個物件，該物件可以被一個例項(本地資源)或多個例項之間(全域性資源)的不同會話鎖定。每個想試圖鎖定資源的會話都在該資源上生成一個佇列。

下面是Oracle Enqueues對資源申請的鎖模式和申請資源

Enqueues are usually represented in the format "TYPE-ID1-ID2" where:
"TYPE" is a 2 character text string"ID1" is a 4 byte hexadecimal number
"ID2" is a 4 byte hexadecimal number Parameters:
 P1 = Lock Type & Mode
P2 = Lock ID1
P3 = Lock ID2
Lock Type & Mode
The lock type and requested mode are encoded into P1 thus:
Convert P1 into hexadecimal (or use P1RAW) and extract the lock type and requested mode from this by converting the first 2 bytes of the hexadecimal number to ASCII and the second 2 bytes to a number:
Eg: 54580006
    ^^^^------ Converted to ASCII gives "TX" (0x54 = "T", 0x58 = "X")
        ^^^^-- 0006 is 6 in decimal so this is a mode 6 request

Note that on UNIX, the command 'man ascii' will display the Octal, hexadecimal, and decimal ASCII character sets to help with the hex translation.

An alternative way to extract this information is to use SQL thus:
SELECT chr(to_char(bitand(p1,-16777216))/16777215)||
        chr(to_char(bitand(p1, 16711680))/65535) "Lock",
        to_char( bitand(p1, 65535) )    "Mode"
   FROM v$session_wait
  WHERE event = 'enqueue'
;
Lock ID1
 P2 represents ID1 of the enqueue name in decimal.
P2RAW represents ID1 of the enqueue name in hexadecimal.
Lock ID2
 P3 represents ID2 of the enqueue name in decimal.
P3RAW represents ID2 of the enqueue name in hexadecimal.