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Introduce entropy for fastestmirror option #324

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merged 2 commits into from
Oct 15, 2024
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Introduce entropy for fastestmirror option #324

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af427c8
Introduce entropy for fastestmirror option
PhirePhly Aug 12, 2024
4657146
fastestmirror: Guard against empty mirrorlist and unreachable mirrors
evan-goode Oct 1, 2024
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20 changes: 19 additions & 1 deletion librepo/fastestmirror.c
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Original file line number Diff line number Diff line change
Expand Up @@ -694,10 +694,28 @@ lr_fastestmirror(LrHandle *handle,
}

// Sort the mirrors by the connection time
//
// Note that always picking the single best mirror has undesirable properties like
// forcing the user to always pick the single lowest latency mirror regardless of its
// actual bandwidth performance, and high density install bases all using fastestmirror
// tend to dogpile the single mirror nearest to all of them
//
// Instead of using a strict sorted list, shuffle all mirrors with lower latency than 2x
// the best mirror, to introduce enough entropy to spread the load across nearby mirrors.
double bestMirrorLatency = 0;
if (lrfastestmirrors != NULL) {
bestMirrorLatency = ((LrFastestMirror *)lrfastestmirrors->data)->plain_connect_time;
}

for (GSList *elem = lrfastestmirrors; elem; elem = g_slist_next(elem)) {
LrFastestMirror *mirror = elem->data;
g_debug("%s: %3.6f : %s", __func__, mirror->plain_connect_time, mirror->url);
new_list = g_slist_append(new_list, mirror->url);
if (mirror->plain_connect_time >= 0 &&
mirror->plain_connect_time < (2.0 * bestMirrorLatency)) { // Shuffle nearby mirrors
new_list = g_slist_insert(new_list, mirror->url, g_random_int_range(0, g_slist_length(new_list)+1));
} else { // Far away mirrors appended as backup options
new_list = g_slist_append(new_list, mirror->url);
}
}

g_slist_free_full(lrfastestmirrors, (GDestroyNotify)lr_lrfastestmirror_free);
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