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Re: [PATCH] Improve performance when starting nginx with a lot of locations

Yusuke Nojima
October 11, 2023 06:34AM
Thank you for your comments and implementation!
I am looking forward to the acceleration of nginx startup with this patch.

2023年10月11日(水) 7:56 Maxim Dounin <mdounin@mdounin.ru>:
>
> Hello!
>
> On Thu, Oct 05, 2023 at 10:51:26AM +0900, Yusuke Nojima wrote:
>
> > Thank you for your comment!
> >
> > > Could you please provide some more details about the use case,
> > > such as how locations are used, and what is the approximate number
> > > of locations being used?
> >
> > Our team provides development environments to our company's engineers and QA.
> > In this environment, engineers and QA can freely create VMs and deploy
> > applications on them.
> >
> > Our nginx has the role of routing requests from the internet to all
> > applications deployed in this environment.
> > Additionally, it allows setting IP address restrictions, BASIC
> > authentication, TLS client authentication, and other configurations
> > for each application.
> >
> > To implement these requirements, we generate a location for each application.
> > Currently, there are approximately 40,000 locations in our environment.
>
> Thank you for the details. Such configuration looks somewhat
> sub-optimal, but understandable for a development / test
> environment. And certainly 40k locations is a lot for the sorting
> algorithm currently used.
>
> > > Further, since each location contains configuration for
> > > all modules, such configurations are expected to require a lot of
> > > memory
> >
> > Each of our nginx processes was consuming 5GB of memory in terms of
> > resident size.
> > This is not a problem as our servers have sufficient memory.
> >
> > > Rather, I would suggest recursive top-bottom merge sort implementation
> > > instead, which is much simpler and uses stack as temporary storage
> > > (so it'll naturally die if there will be a queue which requires
> > > more space for sorting than we have).
> > >
> > > Please take a look if it works for you:
> >
> > I think this implementation is simple and easy to understand.
> > Although the number of traversals of the list will increase compared
> > to bottom-up, it will not affect the order.
> > I believe this will provide sufficient optimization in terms of speed.
>
> Thanks for looking. In my limited testing, it is slightly faster
> than your bottom-up implementation (and significantly faster than
> the existing insertion sort when many locations are used).
>
> Below is the full patch (code unchanged), I'll commit it as soon
> as some other nginx developer will review it.
>
> # HG changeset patch
> # User Maxim Dounin <mdounin@mdounin.ru>
> # Date 1696977468 -10800
> # Wed Oct 11 01:37:48 2023 +0300
> # Node ID b891840852ee5cc823eee1769d092ab50928919f
> # Parent cdda286c0f1b4b10f30d4eb6a63fefb9b8708ecc
> Core: changed ngx_queue_sort() to use merge sort.
>
> This improves nginx startup times significantly when using very large number
> of locations due computational complexity of the sorting algorithm being
> used (insertion sort is O(n*n) on average, while merge sort is O(n*log(n))).
> In particular, in a test configuration with 20k locations total startup
> time is reduced from 8 seconds to 0.9 seconds.
>
> Prodded by Yusuke Nojima,
> https://mailman.nginx.org/pipermail/nginx-devel/2023-September/NUL3Y2FPPFSHMPTFTL65KXSXNTX3NQMK.html
>
> diff --git a/src/core/ngx_queue.c b/src/core/ngx_queue.c
> --- a/src/core/ngx_queue.c
> +++ b/src/core/ngx_queue.c
> @@ -9,6 +9,10 @@
> #include <ngx_core.h>
>
>
> +static void ngx_queue_merge(ngx_queue_t *queue, ngx_queue_t *tail,
> + ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *));
> +
> +
> /*
> * find the middle queue element if the queue has odd number of elements
> * or the first element of the queue's second part otherwise
> @@ -45,13 +49,13 @@ ngx_queue_middle(ngx_queue_t *queue)
> }
>
>
> -/* the stable insertion sort */
> +/* the stable merge sort */
>
> void
> ngx_queue_sort(ngx_queue_t *queue,
> ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> {
> - ngx_queue_t *q, *prev, *next;
> + ngx_queue_t *q, tail;
>
> q = ngx_queue_head(queue);
>
> @@ -59,22 +63,44 @@ ngx_queue_sort(ngx_queue_t *queue,
> return;
> }
>
> - for (q = ngx_queue_next(q); q != ngx_queue_sentinel(queue); q = next) {
> + q = ngx_queue_middle(queue);
> +
> + ngx_queue_split(queue, q, &tail);
> +
> + ngx_queue_sort(queue, cmp);
> + ngx_queue_sort(&tail, cmp);
> +
> + ngx_queue_merge(queue, &tail, cmp);
> +}
>
> - prev = ngx_queue_prev(q);
> - next = ngx_queue_next(q);
>
> - ngx_queue_remove(q);
> +static void
> +ngx_queue_merge(ngx_queue_t *queue, ngx_queue_t *tail,
> + ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> +{
> + ngx_queue_t *q1, *q2;
> +
> + q1 = ngx_queue_head(queue);
> + q2 = ngx_queue_head(tail);
>
> - do {
> - if (cmp(prev, q) <= 0) {
> - break;
> - }
> + for ( ;; ) {
> + if (q1 == ngx_queue_sentinel(queue)) {
> + ngx_queue_add(queue, tail);
> + break;
> + }
> +
> + if (q2 == ngx_queue_sentinel(tail)) {
> + break;
> + }
>
> - prev = ngx_queue_prev(prev);
> + if (cmp(q1, q2) <= 0) {
> + q1 = ngx_queue_next(q1);
> + continue;
> + }
>
> - } while (prev != ngx_queue_sentinel(queue));
> + ngx_queue_remove(q2);
> + ngx_queue_insert_before(q1, q2);
>
> - ngx_queue_insert_after(prev, q);
> + q2 = ngx_queue_head(tail);
> }
> }
> diff --git a/src/core/ngx_queue.h b/src/core/ngx_queue.h
> --- a/src/core/ngx_queue.h
> +++ b/src/core/ngx_queue.h
> @@ -47,6 +47,9 @@ struct ngx_queue_s {
> (h)->prev = x
>
>
> +#define ngx_queue_insert_before ngx_queue_insert_tail
> +
> +
> #define ngx_queue_head(h) \
> (h)->next
>
>
>
>
> >
> >
> > 2023年9月30日(土) 12:38 Maxim Dounin <mdounin@mdounin.ru>:
> > >
> > > Hello!
> > >
> > > On Fri, Sep 22, 2023 at 03:58:41PM +0900, Yusuke Nojima wrote:
> > >
> > > > # HG changeset patch
> > > > # User Yusuke Nojima <nojima@ynojima.com>
> > > > # Date 1679555707 -32400
> > > > # Thu Mar 23 16:15:07 2023 +0900
> > > > # Node ID 6aac98fb135e47ca9cf7ad7d780cf4a10e9aa55c
> > > > # Parent 8771d35d55d0a2b1cefaab04401d6f837f5a05a2
> > > > Improve performance when starting nginx with a lot of locations
> > > >
> > > > Our team has a configuration file with a very large number of
> > > > locations, and we found that starting nginx with this file takes an
> > > > unacceptable amount of time. After investigating the issue, we
> > > > discovered that the root cause of the long startup time is the sorting
> > > > of the location list.
> > >
> > > Interesting.
> > >
> > > Could you please provide some more details about the use case,
> > > such as how locations are used, and what is the approximate number
> > > of locations being used?
> > >
> > > In my practice, it is extremely uncommon to use more than 1k-10k
> > > prefix locations (and even these numbers are huge for normal
> > > setups). Further, since each location contains configuration for
> > > all modules, such configurations are expected to require a lot of
> > > memory (currently about 5-10KB per empty location, so about
> > > 50-100MB per 10k locations, and 0.5-1G per 100k locations).
> > > Accordingly, using other approaches such as map (assuming exact
> > > match is actually needed) might be beneficial regardless of the
> > > sorting costs.
> > >
> > > Nevertheless, swapping the sorting algorithm to a faster one looks
> > > like an obvious improvement.
> > >
> > > >
> > > > Currently, the sorting algorithm used in nginx is insertion sort,
> > > > which requires O(n^2) time for n locations. We have modified the
> > > > sorting algorithm to use merge sort instead, which has a time
> > > > complexity of O(n log n).
> > > >
> > > > We have tested the modified code using micro-benchmarks and confirmed
> > > > that the new algorithm improves nginx startup time significantly
> > > > (shown below). We believe that this change would be valuable for other
> > > > users who are experiencing similar issues.
> > > >
> > > >
> > > > Table: nginx startup time in seconds
> > > >
> > > > n current patched
> > > > 2000 0.033 0.018
> > > > 4000 0.047 0.028
> > > > 6000 0.062 0.038
> > > > 8000 0.079 0.050
> > > > 10000 0.091 0.065
> > > > 12000 0.367 0.081
> > > > 14000 0.683 0.086
> > > > 16000 0.899 0.097
> > > > 18000 1.145 0.110
> > > > 20000 1.449 0.122
> > > > 22000 1.650 0.137
> > > > 24000 2.155 0.151
> > > > 26000 3.096 0.155
> > > > 28000 3.711 0.168
> > > > 30000 3.539 0.184
> > > > 32000 3.980 0.193
> > > > 34000 4.543 0.208
> > > > 36000 4.349 0.217
> > > > 38000 5.021 0.229
> > > > 40000 4.918 0.245
> > > > 42000 4.835 0.256
> > > > 44000 5.159 0.262
> > > > 46000 5.802 0.331
> > > > 48000 6.205 0.295
> > > > 50000 5.701 0.308
> > > > 52000 5.992 0.335
> > > > 54000 6.561 0.323
> > > > 56000 6.856 0.333
> > > > 58000 6.515 0.347
> > > > 60000 7.051 0.359
> > > > 62000 6.956 0.377
> > > > 64000 7.376 0.376
> > > > 66000 7.506 0.404
> > > > 68000 7.292 0.407
> > > > 70000 7.422 0.461
> > > > 72000 10.090 0.443
> > > > 74000 18.505 0.463
> > > > 76000 11.857 0.462
> > > > 78000 9.752 0.470
> > > > 80000 12.485 0.481
> > > > 82000 11.027 0.498
> > > > 84000 9.804 0.523
> > > > 86000 8.482 0.515
> > > > 88000 9.838 0.560
> > > > 90000 12.341 0.546
> > > > 92000 13.881 0.648
> > > > 94000 8.309 0.635
> > > > 96000 8.854 0.650
> > > > 98000 12.871 0.674
> > > > 100000 8.261 0.698
> > >
> > > This probably can be reduced to something like 3-5 data points.
> > >
> > > >
> > > > diff -r 8771d35d55d0 -r 6aac98fb135e src/core/ngx_queue.c
> > > > --- a/src/core/ngx_queue.c Fri Mar 10 07:43:50 2023 +0300
> > > > +++ b/src/core/ngx_queue.c Thu Mar 23 16:15:07 2023 +0900
> > > > @@ -45,36 +45,103 @@
> > > > }
> > > >
> > > >
> > > > -/* the stable insertion sort */
> > > > +/* merge queue2 into queue1. queue2 becomes empty after merge. */
> > > > +
> > > > +static void
> > > > +ngx_queue_merge(ngx_queue_t *queue1, ngx_queue_t *queue2,
> > > > + ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> > > > +{
> > > > + ngx_queue_t *p1, *p2;
> > >
> > > Nitpicking: there are various style issues here and in other places.
> > >
> > > > +
> > > > + p1 = ngx_queue_head(queue1);
> > > > + p2 = ngx_queue_head(queue2);
> > > > +
> > > > + while (p1 != ngx_queue_sentinel(queue1)
> > > > + && p2 != ngx_queue_sentinel(queue2)) {
> > > > +
> > > > + if (cmp(p1, p2) > 0) {
> > > > + ngx_queue_t *next, *prev;
> > > > +
> > > > + next = ngx_queue_next(p2);
> > > > + ngx_queue_remove(p2);
> > > > + prev = ngx_queue_prev(p1);
> > > > + ngx_queue_insert_after(prev, p2);
> > > > + p2 = next;
> > >
> > > Nitpicking: there is no need to preserve "next" here, since p2 is
> > > always the head of queue2 and, and the next element can be
> > > obtained by ngx_queue_head(queue2).
> > >
> > > Also, instead of obtaining "prev" and using
> > > ngx_queue_insert_after() it would be easier to use
> > > ngx_queue_insert_before(). It is not currently defined, but it is
> > > trivial to define one: it is an alias to ngx_queue_insert_tail(),
> > > much like ngx_queue_insert_after() is an alias to
> > > ngx_queue_insert_head().
> > >
> > > > + } else {
> > > > + p1 = ngx_queue_next(p1);
> > > > + }
> > > > + }
> > > > + if (p2 != ngx_queue_sentinel(queue2)) {
> > > > + ngx_queue_add(queue1, queue2);
> > > > + ngx_queue_init(queue2);
> > > > + }
> > > > +}
> > > > +
> > > > +
> > > > +/* move all elements from src to dest. dest should be empty before call. */
> > > > +
> > > > +static void
> > > > +ngx_queue_move(ngx_queue_t *dest, ngx_queue_t *src)
> > > > +{
> > > > + *dest = *src;
> > > > + ngx_queue_init(src);
> > > > +
> > > > + if (dest->next == src) {
> > > > + dest->next = dest;
> > > > + } else {
> > > > + dest->next->prev = dest;
> > > > + }
> > > > + if (dest->prev == src) {
> > > > + dest->prev = dest;
> > > > + } else {
> > > > + dest->prev->next = dest;
> > > > + }
> > > > +}
> > >
> > > This function looks strange to me. There is the ngx_queue_add()
> > > macro, which probably should be used instead (if needed).
> > >
> > > > +
> > > > +
> > > > +/* the stable merge sort */
> > > >
> > > > void
> > > > ngx_queue_sort(ngx_queue_t *queue,
> > > > ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> > > > {
> > > > - ngx_queue_t *q, *prev, *next;
> > > > + ngx_queue_t merged[64], *p, *last;
> > > >
> > > > - q = ngx_queue_head(queue);
> > > > -
> > > > - if (q == ngx_queue_last(queue)) {
> > > > + if (ngx_queue_head(queue) == ngx_queue_last(queue)) {
> > > > return;
> > > > }
> > > >
> > > > - for (q = ngx_queue_next(q); q != ngx_queue_sentinel(queue); q = next) {
> > > > + last = merged;
> > > >
> > > > - prev = ngx_queue_prev(q);
> > > > - next = ngx_queue_next(q);
> > > > + while (!ngx_queue_empty(queue)) {
> > > > + /*
> > > > + * Loop invariant:
> > > > + * merged[i] must have exactly 0 or 2^i elements in sorted order.
> > > > + * For each iteration, we take one element from the given queue and
> > > > + * insert it into merged without violating the invariant condition.
> > > > + */
> > > >
> > > > - ngx_queue_remove(q);
> > > > + ngx_queue_t carry, *h;
> > > > +
> > > > + h = ngx_queue_head(queue);
> > > > + ngx_queue_remove(h);
> > > > + ngx_queue_init(&carry);
> > > > + ngx_queue_insert_head(&carry, h);
> > > >
> > > > - do {
> > > > - if (cmp(prev, q) <= 0) {
> > > > - break;
> > > > - }
> > > > + for (p = merged; p != last && !ngx_queue_empty(p); p++) {
> > > > + ngx_queue_merge(p, &carry, cmp);
> > > > + ngx_queue_move(&carry, p);
> > > > + }
> > > > + if (p == last) {
> > > > + ngx_queue_init(last);
> > > > + last++;
> > > > + }
> > > > + ngx_queue_move(p, &carry);
> > > > + }
> > > >
> > > > - prev = ngx_queue_prev(prev);
> > > > -
> > > > - } while (prev != ngx_queue_sentinel(queue));
> > > > -
> > > > - ngx_queue_insert_after(prev, q);
> > > > + /* Merge all queues into one queue */
> > > > + for (p = merged + 1; p != last; p++) {
> > > > + ngx_queue_merge(p, p-1, cmp);
> > > > }
> > > > + ngx_queue_move(queue, last-1);
> > > > }
> > >
> > > While bottom-up merge sort implementation might be more efficient,
> > > I find it disturbing to use fixed array of queues without any
> > > checks if we are within the array bounds.
> > >
> > > Rather, I would suggest recursive top-bottom merge sort implementation
> > > instead, which is much simpler and uses stack as temporary storage
> > > (so it'll naturally die if there will be a queue which requires
> > > more space for sorting than we have).
> > >
> > > Please take a look if it works for you:
> > >
> > > diff --git a/src/core/ngx_queue.c b/src/core/ngx_queue.c
> > > --- a/src/core/ngx_queue.c
> > > +++ b/src/core/ngx_queue.c
> > > @@ -9,6 +9,10 @@
> > > #include <ngx_core.h>
> > >
> > >
> > > +static void ngx_queue_merge(ngx_queue_t *queue, ngx_queue_t *tail,
> > > + ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *));
> > > +
> > > +
> > > /*
> > > * find the middle queue element if the queue has odd number of elements
> > > * or the first element of the queue's second part otherwise
> > > @@ -45,13 +49,13 @@ ngx_queue_middle(ngx_queue_t *queue)
> > > }
> > >
> > >
> > > -/* the stable insertion sort */
> > > +/* the stable merge sort */
> > >
> > > void
> > > ngx_queue_sort(ngx_queue_t *queue,
> > > ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> > > {
> > > - ngx_queue_t *q, *prev, *next;
> > > + ngx_queue_t *q, tail;
> > >
> > > q = ngx_queue_head(queue);
> > >
> > > @@ -59,22 +63,44 @@ ngx_queue_sort(ngx_queue_t *queue,
> > > return;
> > > }
> > >
> > > - for (q = ngx_queue_next(q); q != ngx_queue_sentinel(queue); q = next) {
> > > + q = ngx_queue_middle(queue);
> > > +
> > > + ngx_queue_split(queue, q, &tail);
> > > +
> > > + ngx_queue_sort(queue, cmp);
> > > + ngx_queue_sort(&tail, cmp);
> > > +
> > > + ngx_queue_merge(queue, &tail, cmp);
> > > +}
> > >
> > > - prev = ngx_queue_prev(q);
> > > - next = ngx_queue_next(q);
> > >
> > > - ngx_queue_remove(q);
> > > +static void
> > > +ngx_queue_merge(ngx_queue_t *queue, ngx_queue_t *tail,
> > > + ngx_int_t (*cmp)(const ngx_queue_t *, const ngx_queue_t *))
> > > +{
> > > + ngx_queue_t *q1, *q2;
> > > +
> > > + q1 = ngx_queue_head(queue);
> > > + q2 = ngx_queue_head(tail);
> > >
> > > - do {
> > > - if (cmp(prev, q) <= 0) {
> > > - break;
> > > - }
> > > + for ( ;; ) {
> > > + if (q1 == ngx_queue_sentinel(queue)) {
> > > + ngx_queue_add(queue, tail);
> > > + break;
> > > + }
> > > +
> > > + if (q2 == ngx_queue_sentinel(tail)) {
> > > + break;
> > > + }
> > >
> > > - prev = ngx_queue_prev(prev);
> > > + if (cmp(q1, q2) <= 0) {
> > > + q1 = ngx_queue_next(q1);
> > > + continue;
> > > + }
> > >
> > > - } while (prev != ngx_queue_sentinel(queue));
> > > + ngx_queue_remove(q2);
> > > + ngx_queue_insert_before(q1, q2);
> > >
> > > - ngx_queue_insert_after(prev, q);
> > > + q2 = ngx_queue_head(tail);
> > > }
> > > }
> > > diff --git a/src/core/ngx_queue.h b/src/core/ngx_queue.h
> > > --- a/src/core/ngx_queue.h
> > > +++ b/src/core/ngx_queue.h
> > > @@ -47,6 +47,9 @@ struct ngx_queue_s {
> > > (h)->prev = x
> > >
> > >
> > > +#define ngx_queue_insert_before ngx_queue_insert_tail
> > > +
> > > +
> > > #define ngx_queue_head(h) \
> > > (h)->next
> > >
> > >
> > >
> > > --
> > > Maxim Dounin
> > > http://mdounin.ru/
> > > _______________________________________________
> > > nginx-devel mailing list
> > > nginx-devel@nginx.org
> > > https://mailman.nginx.org/mailman/listinfo/nginx-devel
> > _______________________________________________
> > nginx-devel mailing list
> > nginx-devel@nginx.org
> > https://mailman.nginx.org/mailman/listinfo/nginx-devel
>
> --
> Maxim Dounin
> http://mdounin.ru/
> _______________________________________________
> nginx-devel mailing list
> nginx-devel@nginx.org
> https://mailman.nginx.org/mailman/listinfo/nginx-devel
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Subject Author Views Posted

[PATCH] Improve performance when starting nginx with a lot of locations

Yusuke Nojima 368 September 22, 2023 03:00AM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Maxim Dounin 86 September 29, 2023 11:40PM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Yusuke Nojima 69 October 04, 2023 09:52PM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Илья Шипицин 88 October 05, 2023 02:18AM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Yusuke Nojima 77 October 05, 2023 10:40PM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Maxim Dounin 66 October 10, 2023 06:58PM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Yusuke Nojima 70 October 11, 2023 06:34AM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Sergey Kandaurov 67 October 17, 2023 07:26AM

Re: [PATCH] Improve performance when starting nginx with a lot of locations

Maxim Dounin 90 October 17, 2023 10:04PM



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