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-rw-r--r--src/lb_chash.c517
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diff --git a/src/lb_chash.c b/src/lb_chash.c
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+/*
+ * Consistent Hash implementation
+ * Please consult this very well detailed article for more information :
+ * http://www.spiteful.com/2008/03/17/programmers-toolbox-part-3-consistent-hashing/
+ *
+ * Our implementation has to support both weighted hashing and weighted round
+ * robin because we'll use it to replace the previous map-based implementation
+ * which offered both algorithms.
+ *
+ * Copyright 2000-2010 Willy Tarreau <w@1wt.eu>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <import/eb32tree.h>
+#include <haproxy/api.h>
+#include <haproxy/backend.h>
+#include <haproxy/errors.h>
+#include <haproxy/queue.h>
+#include <haproxy/server-t.h>
+#include <haproxy/tools.h>
+
+/* Return next tree node after <node> which must still be in the tree, or be
+ * NULL. Lookup wraps around the end to the beginning. If the next node is the
+ * same node, return NULL. This is designed to find a valid next node before
+ * deleting one from the tree.
+ */
+static inline struct eb32_node *chash_skip_node(struct eb_root *root, struct eb32_node *node)
+{
+ struct eb32_node *stop = node;
+
+ if (!node)
+ return NULL;
+ node = eb32_next(node);
+ if (!node)
+ node = eb32_first(root);
+ if (node == stop)
+ return NULL;
+ return node;
+}
+
+/* Remove all of a server's entries from its tree. This may be used when
+ * setting a server down.
+ */
+static inline void chash_dequeue_srv(struct server *s)
+{
+ while (s->lb_nodes_now > 0) {
+ if (s->lb_nodes_now >= s->lb_nodes_tot) // should always be false anyway
+ s->lb_nodes_now = s->lb_nodes_tot;
+ s->lb_nodes_now--;
+ if (s->proxy->lbprm.chash.last == &s->lb_nodes[s->lb_nodes_now].node)
+ s->proxy->lbprm.chash.last = chash_skip_node(s->lb_tree, s->proxy->lbprm.chash.last);
+ eb32_delete(&s->lb_nodes[s->lb_nodes_now].node);
+ }
+}
+
+/* Adjust the number of entries of a server in its tree. The server must appear
+ * as many times as its weight indicates it. If it's there too often, we remove
+ * the last occurrences. If it's not there enough, we add more occurrences. To
+ * remove a server from the tree, normally call this with eweight=0.
+ *
+ * The server's lock and the lbprm's lock must be held.
+ */
+static inline void chash_queue_dequeue_srv(struct server *s)
+{
+ while (s->lb_nodes_now > s->next_eweight) {
+ if (s->lb_nodes_now >= s->lb_nodes_tot) // should always be false anyway
+ s->lb_nodes_now = s->lb_nodes_tot;
+ s->lb_nodes_now--;
+ if (s->proxy->lbprm.chash.last == &s->lb_nodes[s->lb_nodes_now].node)
+ s->proxy->lbprm.chash.last = chash_skip_node(s->lb_tree, s->proxy->lbprm.chash.last);
+ eb32_delete(&s->lb_nodes[s->lb_nodes_now].node);
+ }
+
+ /* Attempt to increase the total number of nodes, if the user
+ * increased the weight beyond the original weight
+ */
+ if (s->lb_nodes_tot < s->next_eweight) {
+ struct tree_occ *new_nodes;
+
+ /* First we need to remove all server's entries from its tree
+ * because the realloc will change all nodes pointers */
+ chash_dequeue_srv(s);
+
+ new_nodes = realloc(s->lb_nodes, s->next_eweight * sizeof(*new_nodes));
+ if (new_nodes) {
+ unsigned int j;
+
+ s->lb_nodes = new_nodes;
+ memset(&s->lb_nodes[s->lb_nodes_tot], 0,
+ (s->next_eweight - s->lb_nodes_tot) * sizeof(*s->lb_nodes));
+ for (j = s->lb_nodes_tot; j < s->next_eweight; j++) {
+ s->lb_nodes[j].server = s;
+ s->lb_nodes[j].node.key = full_hash(s->puid * SRV_EWGHT_RANGE + j);
+ }
+ s->lb_nodes_tot = s->next_eweight;
+ }
+ }
+ while (s->lb_nodes_now < s->next_eweight) {
+ if (s->lb_nodes_now >= s->lb_nodes_tot) // should always be false anyway
+ break;
+ if (s->proxy->lbprm.chash.last == &s->lb_nodes[s->lb_nodes_now].node)
+ s->proxy->lbprm.chash.last = chash_skip_node(s->lb_tree, s->proxy->lbprm.chash.last);
+ eb32_insert(s->lb_tree, &s->lb_nodes[s->lb_nodes_now].node);
+ s->lb_nodes_now++;
+ }
+}
+
+/* This function updates the server trees according to server <srv>'s new
+ * state. It should be called when server <srv>'s status changes to down.
+ * It is not important whether the server was already down or not. It is not
+ * important either that the new state is completely down (the caller may not
+ * know all the variables of a server's state).
+ *
+ * The server's lock must be held. The lbprm lock will be used.
+ */
+static void chash_set_server_status_down(struct server *srv)
+{
+ struct proxy *p = srv->proxy;
+
+ if (!srv_lb_status_changed(srv))
+ return;
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+
+ if (srv_willbe_usable(srv))
+ goto out_update_state;
+
+ if (!srv_currently_usable(srv))
+ /* server was already down */
+ goto out_update_backend;
+
+ if (srv->flags & SRV_F_BACKUP) {
+ p->lbprm.tot_wbck -= srv->cur_eweight;
+ p->srv_bck--;
+
+ if (srv == p->lbprm.fbck) {
+ /* we lost the first backup server in a single-backup
+ * configuration, we must search another one.
+ */
+ struct server *srv2 = p->lbprm.fbck;
+ do {
+ srv2 = srv2->next;
+ } while (srv2 &&
+ !((srv2->flags & SRV_F_BACKUP) &&
+ srv_willbe_usable(srv2)));
+ p->lbprm.fbck = srv2;
+ }
+ } else {
+ p->lbprm.tot_wact -= srv->cur_eweight;
+ p->srv_act--;
+ }
+
+ chash_dequeue_srv(srv);
+
+out_update_backend:
+ /* check/update tot_used, tot_weight */
+ update_backend_weight(p);
+ out_update_state:
+ srv_lb_commit_status(srv);
+
+ HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+}
+
+/* This function updates the server trees according to server <srv>'s new
+ * state. It should be called when server <srv>'s status changes to up.
+ * It is not important whether the server was already down or not. It is not
+ * important either that the new state is completely UP (the caller may not
+ * know all the variables of a server's state). This function will not change
+ * the weight of a server which was already up.
+ *
+ * The server's lock must be held. The lbprm lock will be used.
+ */
+static void chash_set_server_status_up(struct server *srv)
+{
+ struct proxy *p = srv->proxy;
+
+ if (!srv_lb_status_changed(srv))
+ return;
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+
+ if (!srv_willbe_usable(srv))
+ goto out_update_state;
+
+ if (srv_currently_usable(srv))
+ /* server was already up */
+ goto out_update_backend;
+
+ if (srv->flags & SRV_F_BACKUP) {
+ p->lbprm.tot_wbck += srv->next_eweight;
+ p->srv_bck++;
+
+ if (!(p->options & PR_O_USE_ALL_BK)) {
+ if (!p->lbprm.fbck) {
+ /* there was no backup server anymore */
+ p->lbprm.fbck = srv;
+ } else {
+ /* we may have restored a backup server prior to fbck,
+ * in which case it should replace it.
+ */
+ struct server *srv2 = srv;
+ do {
+ srv2 = srv2->next;
+ } while (srv2 && (srv2 != p->lbprm.fbck));
+ if (srv2)
+ p->lbprm.fbck = srv;
+ }
+ }
+ } else {
+ p->lbprm.tot_wact += srv->next_eweight;
+ p->srv_act++;
+ }
+
+ /* note that eweight cannot be 0 here */
+ chash_queue_dequeue_srv(srv);
+
+ out_update_backend:
+ /* check/update tot_used, tot_weight */
+ update_backend_weight(p);
+ out_update_state:
+ srv_lb_commit_status(srv);
+
+ HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+}
+
+/* This function must be called after an update to server <srv>'s effective
+ * weight. It may be called after a state change too.
+ *
+ * The server's lock must be held. The lbprm lock may be used.
+ */
+static void chash_update_server_weight(struct server *srv)
+{
+ int old_state, new_state;
+ struct proxy *p = srv->proxy;
+
+ if (!srv_lb_status_changed(srv))
+ return;
+
+ /* If changing the server's weight changes its state, we simply apply
+ * the procedures we already have for status change. If the state
+ * remains down, the server is not in any tree, so it's as easy as
+ * updating its values. If the state remains up with different weights,
+ * there are some computations to perform to find a new place and
+ * possibly a new tree for this server.
+ */
+
+ old_state = srv_currently_usable(srv);
+ new_state = srv_willbe_usable(srv);
+
+ if (!old_state && !new_state) {
+ srv_lb_commit_status(srv);
+ return;
+ }
+ else if (!old_state && new_state) {
+ chash_set_server_status_up(srv);
+ return;
+ }
+ else if (old_state && !new_state) {
+ chash_set_server_status_down(srv);
+ return;
+ }
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+
+ /* only adjust the server's presence in the tree */
+ chash_queue_dequeue_srv(srv);
+
+ if (srv->flags & SRV_F_BACKUP)
+ p->lbprm.tot_wbck += srv->next_eweight - srv->cur_eweight;
+ else
+ p->lbprm.tot_wact += srv->next_eweight - srv->cur_eweight;
+
+ update_backend_weight(p);
+ srv_lb_commit_status(srv);
+
+ HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+}
+
+/*
+ * This function implements the "Consistent Hashing with Bounded Loads" algorithm
+ * of Mirrokni, Thorup, and Zadimoghaddam (arxiv:1608.01350), adapted for use with
+ * unequal server weights.
+ */
+int chash_server_is_eligible(struct server *s)
+{
+ /* The total number of slots to allocate is the total number of outstanding requests
+ * (including the one we're about to make) times the load-balance-factor, rounded up.
+ */
+ unsigned tot_slots = ((s->proxy->served + 1) * s->proxy->lbprm.hash_balance_factor + 99) / 100;
+ unsigned slots_per_weight = tot_slots / s->proxy->lbprm.tot_weight;
+ unsigned remainder = tot_slots % s->proxy->lbprm.tot_weight;
+
+ /* Allocate a whole number of slots per weight unit... */
+ unsigned slots = s->cur_eweight * slots_per_weight;
+
+ /* And then distribute the rest among servers proportionally to their weight. */
+ slots += ((s->cumulative_weight + s->cur_eweight) * remainder) / s->proxy->lbprm.tot_weight
+ - (s->cumulative_weight * remainder) / s->proxy->lbprm.tot_weight;
+
+ /* But never leave a server with 0. */
+ if (slots == 0)
+ slots = 1;
+
+ return s->served < slots;
+}
+
+/*
+ * This function returns the running server from the CHASH tree, which is at
+ * the closest distance from the value of <hash>. Doing so ensures that even
+ * with a well imbalanced hash, if some servers are close to each other, they
+ * will still both receive traffic. If any server is found, it will be returned.
+ * It will also skip server <avoid> if the hash result ends on this one.
+ * If no valid server is found, NULL is returned.
+ *
+ * The lbprm's lock will be used in R/O mode. The server's lock is not used.
+ */
+struct server *chash_get_server_hash(struct proxy *p, unsigned int hash, const struct server *avoid)
+{
+ struct eb32_node *next, *prev;
+ struct server *nsrv, *psrv;
+ struct eb_root *root;
+ unsigned int dn, dp;
+ int loop;
+
+ HA_RWLOCK_RDLOCK(LBPRM_LOCK, &p->lbprm.lock);
+
+ if (p->srv_act)
+ root = &p->lbprm.chash.act;
+ else if (p->lbprm.fbck) {
+ nsrv = p->lbprm.fbck;
+ goto out;
+ }
+ else if (p->srv_bck)
+ root = &p->lbprm.chash.bck;
+ else {
+ nsrv = NULL;
+ goto out;
+ }
+
+ /* find the node after and the node before */
+ next = eb32_lookup_ge(root, hash);
+ if (!next)
+ next = eb32_first(root);
+ if (!next) {
+ nsrv = NULL; /* tree is empty */
+ goto out;
+ }
+
+ prev = eb32_prev(next);
+ if (!prev)
+ prev = eb32_last(root);
+
+ nsrv = eb32_entry(next, struct tree_occ, node)->server;
+ psrv = eb32_entry(prev, struct tree_occ, node)->server;
+
+ /* OK we're located between two servers, let's
+ * compare distances between hash and the two servers
+ * and select the closest server.
+ */
+ dp = hash - prev->key;
+ dn = next->key - hash;
+
+ if (dp <= dn) {
+ next = prev;
+ nsrv = psrv;
+ }
+
+ loop = 0;
+ while (nsrv == avoid || (p->lbprm.hash_balance_factor && !chash_server_is_eligible(nsrv))) {
+ next = eb32_next(next);
+ if (!next) {
+ next = eb32_first(root);
+ if (++loop > 1) // protection against accidental loop
+ break;
+ }
+ nsrv = eb32_entry(next, struct tree_occ, node)->server;
+ }
+
+ out:
+ HA_RWLOCK_RDUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+ return nsrv;
+}
+
+/* Return next server from the CHASH tree in backend <p>. If the tree is empty,
+ * return NULL. Saturated servers are skipped.
+ *
+ * The lbprm's lock will be used in R/W mode. The server's lock is not used.
+ */
+struct server *chash_get_next_server(struct proxy *p, struct server *srvtoavoid)
+{
+ struct server *srv, *avoided;
+ struct eb32_node *node, *stop, *avoided_node;
+ struct eb_root *root;
+
+ srv = avoided = NULL;
+ avoided_node = NULL;
+
+ HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+ if (p->srv_act)
+ root = &p->lbprm.chash.act;
+ else if (p->lbprm.fbck) {
+ srv = p->lbprm.fbck;
+ goto out;
+ }
+ else if (p->srv_bck)
+ root = &p->lbprm.chash.bck;
+ else {
+ srv = NULL;
+ goto out;
+ }
+
+ stop = node = p->lbprm.chash.last;
+ do {
+ struct server *s;
+
+ if (node)
+ node = eb32_next(node);
+ if (!node)
+ node = eb32_first(root);
+
+ p->lbprm.chash.last = node;
+ if (!node) {
+ /* no node is available */
+ srv = NULL;
+ goto out;
+ }
+
+ /* Note: if we came here after a down/up cycle with no last
+ * pointer, and after a redispatch (srvtoavoid is set), we
+ * must set stop to non-null otherwise we can loop forever.
+ */
+ if (!stop)
+ stop = node;
+
+ /* OK, we have a server. However, it may be saturated, in which
+ * case we don't want to reconsider it for now, so we'll simply
+ * skip it. Same if it's the server we try to avoid, in which
+ * case we simply remember it for later use if needed.
+ */
+ s = eb32_entry(node, struct tree_occ, node)->server;
+ if (!s->maxconn || (!s->queue.length && s->served < srv_dynamic_maxconn(s))) {
+ if (s != srvtoavoid) {
+ srv = s;
+ break;
+ }
+ avoided = s;
+ avoided_node = node;
+ }
+ } while (node != stop);
+
+ if (!srv) {
+ srv = avoided;
+ p->lbprm.chash.last = avoided_node;
+ }
+
+ out:
+ HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+ return srv;
+}
+
+/* This function is responsible for building the active and backup trees for
+ * consistent hashing. The servers receive an array of initialized nodes
+ * with their assigned keys. It also sets p->lbprm.wdiv to the eweight to
+ * uweight ratio.
+ * Return 0 in case of success, -1 in case of allocation failure.
+ */
+int chash_init_server_tree(struct proxy *p)
+{
+ struct server *srv;
+ struct eb_root init_head = EB_ROOT;
+ int node;
+
+ p->lbprm.set_server_status_up = chash_set_server_status_up;
+ p->lbprm.set_server_status_down = chash_set_server_status_down;
+ p->lbprm.update_server_eweight = chash_update_server_weight;
+ p->lbprm.server_take_conn = NULL;
+ p->lbprm.server_drop_conn = NULL;
+
+ p->lbprm.wdiv = BE_WEIGHT_SCALE;
+ for (srv = p->srv; srv; srv = srv->next) {
+ srv->next_eweight = (srv->uweight * p->lbprm.wdiv + p->lbprm.wmult - 1) / p->lbprm.wmult;
+ srv_lb_commit_status(srv);
+ }
+
+ recount_servers(p);
+ update_backend_weight(p);
+
+ p->lbprm.chash.act = init_head;
+ p->lbprm.chash.bck = init_head;
+ p->lbprm.chash.last = NULL;
+
+ /* queue active and backup servers in two distinct groups */
+ for (srv = p->srv; srv; srv = srv->next) {
+ srv->lb_tree = (srv->flags & SRV_F_BACKUP) ? &p->lbprm.chash.bck : &p->lbprm.chash.act;
+ srv->lb_nodes_tot = srv->uweight * BE_WEIGHT_SCALE;
+ srv->lb_nodes_now = 0;
+ srv->lb_nodes = calloc(srv->lb_nodes_tot,
+ sizeof(*srv->lb_nodes));
+ if (!srv->lb_nodes) {
+ ha_alert("failed to allocate lb_nodes for server %s.\n", srv->id);
+ return -1;
+ }
+ for (node = 0; node < srv->lb_nodes_tot; node++) {
+ srv->lb_nodes[node].server = srv;
+ srv->lb_nodes[node].node.key = full_hash(srv->puid * SRV_EWGHT_RANGE + node);
+ }
+
+ if (srv_currently_usable(srv))
+ chash_queue_dequeue_srv(srv);
+ }
+ return 0;
+}