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refs #5802 Fix calculations for probabilistic clock,

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take into account things could be negative (so use int64_ts instead of uint_64) and set appropriate max for size_current

git-svn-id: file:///svn/toku/tokudb@51207 c7de825b-a66e-492c-adef-691d508d4ae1
This commit is contained in:
Yoni Fogel 2013-04-17 00:01:23 -04:00
parent 3ad68549df
commit 00ac50e3e9
1 changed files with 5 additions and 5 deletions
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10
ft/cachetable.cc
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@ -3771,9 +3771,9 @@ bool evictor::run_eviction_on_pair(PAIR curr_in_clock) {
curr_in_clock->count--;
} else {
// generate a random number between 0 and 2^16
assert(size_current < (1LL<<48)); // to protect against possible overflows
assert(size_current <= (INT64_MAX / ((1<<16)-1))); // to protect against possible overflows
int32_t rnd = myrandom_r(&m_random_data) % (1<<16);
// The if-statement below will be true with probability of
// The if-statement below will be true with probability of
// curr_size/(average size of PAIR in cachetable)
// Here is how the math is done:
// average_size = size_current/n_in_table
@ -3785,10 +3785,10 @@ bool evictor::run_eviction_on_pair(PAIR curr_in_clock) {
// if (2^16*curr_size*n_in_table/size_current > rnd)
// by multiplying each side of the equation by size_current, we get
// if (2^16*curr_size*n_in_table > rnd*size_current)
// and dividing each side by 2^16,
// and dividing each side by 2^16,
// we get the if-clause below
//
if ((((uint64_t)curr_size) * n_in_table) >= (((uint64_t)rnd) * size_current)>>16) {
//
if ((((int64_t)curr_size) * n_in_table) >= (((int64_t)rnd) * size_current)>>16) {
curr_in_clock->count--;
}
}