But the number of balancers does not change yet... And when it
is implemented the overall size of the storage slot should *never*
change. It must be constant, ala the scoreboard.
> On Aug 25, 2015, at 8:39 AM, Yann Ylavic <ylavic....@gmail.com> wrote:
>
> At every startup, in balancer_post_config:
> conf->max_balancers = conf->balancers->nelts + conf->bgrowth;
>
> which means that if you add a balancer and restart, storage->create()
> (eg. slotmem_create) will try to find an existing slot with this ID
> and the exact ALIGNED_PROXY_BALANCER_SHARED_SIZE * conf->max_balancers
> size, and fail:
> if (apr_shm_size_get(shm) != size) {
> apr_shm_detach(shm);
> ap_log_error(APLOG_MARK, APLOG_ERR, 0, ap_server_conf, APLOGNO(02599)
> "existing shared memory for %s could not be used
> (failed size check)",
> fname);
> return APR_EINVAL;
> }
>
> By using storage->attach() first (which is based on the ID only and
> returns the existing item_size and item_num), we can do the check
> ourselves and fail only if conf->max_balancers > item_num, allowing
> for balancers to be added thanks to growth margin used at startup.
>
> On Tue, Aug 25, 2015 at 2:12 PM, Jim Jagielski <j...@jagunet.com> wrote:
>> How and when do ALIGNED_PROXY_BALANCER_SHARED_SIZE and conf->max_balancers
>> change???
>>
>>> On Aug 21, 2015, at 8:34 AM, yla...@apache.org wrote:
>>>
>>> Author: ylavic
>>> Date: Fri Aug 21 12:34:02 2015
>>> New Revision: 1696960
>>>
>>> URL: http://svn.apache.org/r1696960
>>> Log:
>>> mod_proxy_balancer: Fix balancers and balancer members reuse on
>>> restart when new ones are added. PR 58024.
>>>
>>> Since slotmem_create() issues a strict check on the size of an existing
>>> slot before reusing it, it won't reuse existing balancers and members when
>>> new ones are added during restart (whereas growth margins would allow it).
>>> Fix this by using slotmem_attach() first and if it succeeds do the checks
>>> based on the returned previous number of existing entries.
>>>
>>> Modified:
>>> httpd/httpd/trunk/CHANGES
>>> httpd/httpd/trunk/docs/log-message-tags/next-number
>>> httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c
>>>
>>> Modified: httpd/httpd/trunk/CHANGES
>>> URL:
>>> http://svn.apache.org/viewvc/httpd/httpd/trunk/CHANGES?rev=1696960&r1=1696959&r2=1696960&view=diff
>>> ==============================================================================
>>> --- httpd/httpd/trunk/CHANGES [utf-8] (original)
>>> +++ httpd/httpd/trunk/CHANGES [utf-8] Fri Aug 21 12:34:02 2015
>>> @@ -1,6 +1,9 @@
>>> -*- coding: utf-8
>>> -*-
>>> Changes with Apache 2.5.0
>>>
>>> + *) mod_proxy_balancer: Fix balancers and balancer members reuse on
>>> + restart when new ones are added. PR 58024. [Yann Ylavic]
>>> +
>>> *) mod_socache_memcache: Add the 'MemcacheConnTTL' directive to control how
>>> long to keep idle connections with the memcache server(s).
>>> Change default value from 600 usec (!) to 15 sec. PR 58091
>>>
>>> Modified: httpd/httpd/trunk/docs/log-message-tags/next-number
>>> URL:
>>> http://svn.apache.org/viewvc/httpd/httpd/trunk/docs/log-message-tags/next-number?rev=1696960&r1=1696959&r2=1696960&view=diff
>>> ==============================================================================
>>> --- httpd/httpd/trunk/docs/log-message-tags/next-number (original)
>>> +++ httpd/httpd/trunk/docs/log-message-tags/next-number Fri Aug 21 12:34:02
>>> 2015
>>> @@ -1 +1 @@
>>> -2964
>>> +2966
>>>
>>> Modified: httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c
>>> URL:
>>> http://svn.apache.org/viewvc/httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c?rev=1696960&r1=1696959&r2=1696960&view=diff
>>> ==============================================================================
>>> --- httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c (original)
>>> +++ httpd/httpd/trunk/modules/proxy/mod_proxy_balancer.c Fri Aug 21
>>> 12:34:02 2015
>>> @@ -761,8 +761,11 @@ static int balancer_post_config(apr_pool
>>> char *id;
>>> proxy_balancer *balancer;
>>> ap_slotmem_type_t type;
>>> + apr_size_t attached_size;
>>> + unsigned int attached_num;
>>> void *sconf = s->module_config;
>>> conf = (proxy_server_conf *)ap_get_module_config(sconf,
>>> &proxy_module);
>>> +
>>> /*
>>> * During create_proxy_config() we created a dummy id. Now that
>>> * we have identifying info, we can create the real id
>>> @@ -794,11 +797,39 @@ static int balancer_post_config(apr_pool
>>> (int)ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>> (int)conf->balancers->nelts, conf->max_balancers);
>>>
>>> - rv = storage->create(&new, conf->id,
>>> - ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>> - conf->max_balancers, type, pconf);
>>> + /* First try to attach() since the number of configured
>>> balancers
>>> + * may have changed during restart, and we don't want create()
>>> to
>>> + * fail because the overall size * number of entries is not
>>> stricly
>>> + * identical to the previous run. There may still be enough
>>> room
>>> + * for this new run thanks to bgrowth margin, so if attach()
>>> + * succeeds we can only check for the number of available
>>> entries
>>> + * to be *greater or* equal to what we need now. If attach()
>>> fails
>>> + * we simply fall back to create().
>>> + */
>>> + rv = storage->attach(&new, conf->id,
>>> + &attached_size, &attached_num,
>>> + pconf);
>>> + if (rv != APR_SUCCESS) {
>>> + rv = storage->create(&new, conf->id,
>>> + ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>> + conf->max_balancers, type, pconf);
>>> + }
>>> + else {
>>> + ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(02964)
>>> + "Balancers attached: %d, %d (%d)",
>>> + (int)ALIGNED_PROXY_BALANCER_SHARED_SIZE,
>>> + (int)attached_num, conf->max_balancers);
>>> + if (attached_size == ALIGNED_PROXY_BALANCER_SHARED_SIZE
>>> + && attached_num >= conf->balancers->nelts) {
>>> + conf->max_balancers = attached_num;
>>> + }
>>> + else {
>>> + rv = APR_ENOSPC;
>>> + }
>>> + }
>>> if (rv != APR_SUCCESS) {
>>> - ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
>>> APLOGNO(01179) "balancer slotmem_create failed");
>>> + ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s, APLOGNO(01179)
>>> + "balancer slotmem create or attach failed");
>>> return !OK;
>>> }
>>> conf->bslot = new;
>>> @@ -864,11 +895,32 @@ static int balancer_post_config(apr_pool
>>> (int)ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>> (int)balancer->max_workers, i);
>>>
>>> - rv = storage->create(&new, balancer->s->sname,
>>> - ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>> - balancer->max_workers, type, pconf);
>>> + /* try to attach first (see rationale from balancers above) */
>>> + rv = storage->attach(&new, balancer->s->sname,
>>> + &attached_size, &attached_num,
>>> + pconf);
>>> + if (rv != APR_SUCCESS) {
>>> + rv = storage->create(&new, balancer->s->sname,
>>> + ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>> + balancer->max_workers, type, pconf);
>>> + }
>>> + else {
>>> + ap_log_error(APLOG_MARK, APLOG_DEBUG, 0, s, APLOGNO(02965)
>>> + "Workers attached: %s (%s), %d, %d (%d) [%u]",
>>> + balancer->s->name, balancer->s->sname,
>>> + (int)ALIGNED_PROXY_WORKER_SHARED_SIZE,
>>> + (int)attached_num, balancer->max_workers, i);
>>> + if (attached_size == ALIGNED_PROXY_WORKER_SHARED_SIZE
>>> + && attached_num >= balancer->workers->nelts) {
>>> + balancer->max_workers = attached_num;
>>> + }
>>> + else {
>>> + rv = APR_ENOSPC;
>>> + }
>>> + }
>>> if (rv != APR_SUCCESS) {
>>> - ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s,
>>> APLOGNO(01185) "worker slotmem_create failed");
>>> + ap_log_error(APLOG_MARK, APLOG_EMERG, rv, s, APLOGNO(01185)
>>> + "worker slotmem create or attach failed");
>>> return !OK;
>>> }
>>> balancer->wslot = new;
>>>
>>>
>>
