111 lines
4.9 KiB
Diff
111 lines
4.9 KiB
Diff
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From ee591233efd57d625fea9057a975281fb8f4d358 Mon Sep 17 00:00:00 2001
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From: Godbach <nylzhaowei@gmail.com>
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Date: Mon, 22 Jul 2013 07:44:53 +0800
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Subject: [PATCH 5/9] BUG/MEDIUM: server: set the macro for server's max weight
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SRV_UWGHT_MAX to SRV_UWGHT_RANGE
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The max weight of server is 256 now, but SRV_UWGHT_MAX is still 255. As a result,
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FWRR will not work well when server's weight is 256. The description is as below:
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There are some macros related to server's weight in include/types/server.h:
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#define SRV_UWGHT_RANGE 256
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#define SRV_UWGHT_MAX (SRV_UWGHT_RANGE - 1)
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#define SRV_EWGHT_MAX (SRV_UWGHT_MAX * BE_WEIGHT_SCALE)
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Since weight of server can be reach to 256 and BE_WEIGHT_SCALE equals to 16,
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the max eweight of server should be 256*16 = 4096, it will exceed SRV_EWGHT_MAX
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which equals to SRV_UWGHT_MAX*BE_WEIGHT_SCALE = 255*16 = 4080. When a server
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with weight 256 is insterted into FWRR tree during initialization, the key value
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of this server should be SRV_EWGHT_MAX - s->eweight = 4080 - 4096 = -16 which
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is closed to UINT_MAX in unsigned type, so the server with highest weight will
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be not elected as the first server to process request.
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In addition, it is a better choice to compare with SRV_UWGHT_MAX than a magic
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number 256 while doing check for the weight. The max number of servers for
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round-robin algorithm is also updated.
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Signed-off-by: Godbach <nylzhaowei@gmail.com>
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(cherry picked from commit a34bdc0ea402ea5be1e9d7f80eaddec772b94393)
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---
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doc/configuration.txt | 2 +-
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include/types/backend.h | 4 ++--
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include/types/server.h | 2 +-
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src/cfgparse.c | 6 +++---
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src/lb_fwrr.c | 2 +-
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5 files changed, 8 insertions(+), 8 deletions(-)
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diff --git a/doc/configuration.txt b/doc/configuration.txt
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index 6e0add7..a008cd7 100644
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--- a/doc/configuration.txt
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+++ b/doc/configuration.txt
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@@ -1141,7 +1141,7 @@ balance url_param <param> [check_post [<max_wait>]]
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processing time remains equally distributed. This algorithm
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is dynamic, which means that server weights may be adjusted
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on the fly for slow starts for instance. It is limited by
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- design to 4128 active servers per backend. Note that in some
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+ design to 4095 active servers per backend. Note that in some
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large farms, when a server becomes up after having been down
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for a very short time, it may sometimes take a few hundreds
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requests for it to be re-integrated into the farm and start
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diff --git a/include/types/backend.h b/include/types/backend.h
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index dc4786e..1067125 100644
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--- a/include/types/backend.h
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+++ b/include/types/backend.h
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@@ -102,8 +102,8 @@
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* weight modulation even with small weights (eg: 1). It should not be too high
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* though because it limits the number of servers in FWRR mode in order to
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* prevent any integer overflow. The max number of servers per backend is
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- * limited to about 2^32/255^2/scale ~= 66051/scale. A scale of 16 looks like
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- * a good value, as it allows more than 4000 servers per backend while leaving
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+ * limited to about (2^32-1)/256^2/scale ~= 65535.9999/scale. A scale of 16
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+ * looks like a good value, as it allows 4095 servers per backend while leaving
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* modulation steps of about 6% for servers with the lowest weight (1).
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*/
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#define BE_WEIGHT_SCALE 16
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diff --git a/include/types/server.h b/include/types/server.h
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index 14e4d1f..9fbd290 100644
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--- a/include/types/server.h
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+++ b/include/types/server.h
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@@ -69,7 +69,7 @@
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/* various constants */
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#define SRV_UWGHT_RANGE 256
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-#define SRV_UWGHT_MAX (SRV_UWGHT_RANGE - 1)
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+#define SRV_UWGHT_MAX (SRV_UWGHT_RANGE)
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#define SRV_EWGHT_RANGE (SRV_UWGHT_RANGE * BE_WEIGHT_SCALE)
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#define SRV_EWGHT_MAX (SRV_UWGHT_MAX * BE_WEIGHT_SCALE)
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diff --git a/src/cfgparse.c b/src/cfgparse.c
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index 345b415..7d349b3 100644
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--- a/src/cfgparse.c
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+++ b/src/cfgparse.c
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@@ -3639,9 +3639,9 @@ stats_error_parsing:
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else if (!strcmp(args[cur_arg], "weight")) {
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int w;
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w = atol(args[cur_arg + 1]);
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- if (w < 0 || w > 256) {
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- Alert("parsing [%s:%d] : weight of server %s is not within 0 and 256 (%d).\n",
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- file, linenum, newsrv->id, w);
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+ if (w < 0 || w > SRV_UWGHT_MAX) {
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+ Alert("parsing [%s:%d] : weight of server %s is not within 0 and %d (%d).\n",
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+ file, linenum, newsrv->id, SRV_UWGHT_MAX, w);
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err_code |= ERR_ALERT | ERR_FATAL;
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goto out;
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}
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diff --git a/src/lb_fwrr.c b/src/lb_fwrr.c
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index d92b6eb..7f5c8a9 100644
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--- a/src/lb_fwrr.c
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+++ b/src/lb_fwrr.c
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@@ -343,7 +343,7 @@ static void fwrr_queue_srv(struct server *s)
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* lower the scale, the rougher the weights modulation, and the
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* higher the scale, the lower the number of servers without
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* overflow. With this formula, the result is always positive,
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- * so we can use eb3<62>_insert().
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+ * so we can use eb32_insert().
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*/
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s->lb_node.key = SRV_UWGHT_RANGE * s->npos +
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(unsigned)(SRV_EWGHT_MAX + s->rweight - s->eweight) / BE_WEIGHT_SCALE;
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--
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1.8.1.5
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