Oracle latch闩原理示意图
Function Get_Latch(latch_name,mode){
If Mode eq ‘immediate’ {
If Fast_Get(latch_name) {
return TRUE
Else {
return FALSE
}
}
Else {
If Fast_Get(latch_name)
Then {
v$latch.gets++
return TRUE
}
Else {
v$latch.misses++
for try = 0 .. large_number
{
if Spin_Get(latch_name)
Then {
return TRUE
}
Else {
T0 = time
Sleep(try)
T1=time
Register_Event("latch free",T1-T0)
}
} -- spin/sleep loop
}
}
}
Function Fast_Get(latch_name)
{
If try_to_get_latch(latch_name)
Then {
return TRUE
}
Else {
return FALSE
}
}
Function Spin_Get(latch_name)
{
v$latch.spin_get++
for i = 1 to _spin_count
{
If Fast_Get(latch_name)
Then {
return TRUE
}
}
}
Function Sleep(try)
{
v$latch.sleeps++
v$latch.sleep++
sleeptime =
decode(try,0,0,1,10,2,20,3,~40,4,~80,...~2000)
sleep(sleeptime)
}
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