thanks for reply how about the length of the number?
1/1000 to which digits should i round ?? 4 or 5 6 digits ? AS AN EXAMPLE the 1/1000 probabilities will have the acls as below : 0.001 0.000999 0.000998001 0.000997002999 0.000996005996001 the question is how many digits should i round ? will squid understand the long digits ? cheers > On Aug 28, 2016, at 2:38 AM, Alex Rousskov <rouss...@measurement-factory.com> > wrote: > > On 08/27/2016 04:34 PM, --Ahmad-- wrote: > >> i guess i need to create probability 1/1000 for each ip. > > Yes, but that is _not_ the same as 1/1000 probability for each > tcp_outgoing_address rule, unfortunately. tcp_outgoing_address rules are > evaluated top to bottom until the first matches. If you have N rules and > each rule has a 1/N probability of a match in isolation, then you will > get the following probabilities of a match when the rules are combined: > > rule #0: 1/N -- good! > rule #1: (1-1/N) * 1/N -- which is not 1/N > rule #2: (1-1/N) * (1-1/N) * 1/N -- even less 1/N than rule #2 was > rule #3: (1-1/N) * (1-1/N) * (1-1/N) * 1/N -- and getting worse! > ... > > To simplify equations, let me denote 1/N as p and (1-1/N) as q. With > your incorrect 1/N ACLs, you get the following probabilities (I am just > rewriting the above using p and q): > > rule #0: p > rule #1: q * p > rule #2: q*q * p > rule #3: q*q*q * p > ... > > If you are still unsure, consider the simple case of just 2 rules > (instead of 1000). You want the second rule to match 50% of the time. If > you give the second rule ACL the same 1/2 probability of a match, then > the second rule will only match 1/4 of the time because it will match > only when the previous rule did _not_ match (1/2) _and_ when its own ACL > matched (1/2): 1/2*1/2 = 1/4. > > > To compensate for the cumulative effect of rules evaluation, you need > rule i to have p/(q^i) probability of a match (where "q^i" is "q to the > power of i"). With that, you will always get the same probability of a > match (p) for each rule when that rule is evaluated: > > rule #0: p > rule #1: q * p/q = p > rule #2: q*q * p/(q*q) = p > rule #3: q*q*q * p/(q*q*q) = p > ... > rule #998: q^998 * p/(q^998) = p > > To avoid uncertainty, the last rule (rule #999 in the above notation) > should use the "all" ACL (i.e., it will always match). > > >> how can i create the randomized acls ??? > > I suggest writing a script that generates 999 ACLs with correct p/(q^i) > probability and the corresponding tcp_outgoing_address lines to match them. > > Please note that computing ~500 random ACL matches for each outgoing > Squid connection (or is it each request?) is not going to be > instantaneous! If you are worried about Squid performance, then you may > want to add custom Squid code to select a random or round-robin IP > address out of a pool of 1000 addresses instead. > > [ It is not going to be easy, but if you do it right, the same new > configuration interface and underlying code can then be applied to other > similar tasks in Squid (e.g., selecting one of several load-balanced > ICAP services). In that case, it would be a welcomed feature that may be > officially accepted. If you decide to make this generally useful, then I > recommend getting your configuration design pre-approved on squid-dev > before you implement anything (or before you pay somebody else to > implement it)! ] > > >> is my settings below is correct ?? > > No. Your ACL(s) and rule probabilities are wrong. See above. > > > HTH, > > Alex. >
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