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Use a random backoff factor for session store with faster retries #423

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Use a random backoff factor for session store with faster retries #423

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9 changes: 4 additions & 5 deletions php_memcached.c
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Original file line number Diff line number Diff line change
Expand Up @@ -370,7 +370,7 @@ PHP_INI_BEGIN()
#ifdef HAVE_MEMCACHED_SESSION
MEMC_SESSION_INI_BOOL ("locking", "1", OnUpdateBool, lock_enabled)
MEMC_SESSION_INI_ENTRY("lock_wait_min", "150", OnUpdateLongGEZero, lock_wait_min)
MEMC_SESSION_INI_ENTRY("lock_wait_max", "150", OnUpdateLongGEZero, lock_wait_max)
MEMC_SESSION_INI_ENTRY("lock_wait_max", "300", OnUpdateLongGEZero, lock_wait_max)
MEMC_SESSION_INI_ENTRY("lock_retries", "5", OnUpdateLong, lock_retries)
MEMC_SESSION_INI_ENTRY("lock_expire", "0", OnUpdateLongGEZero, lock_expiration)
#if defined(LIBMEMCACHED_VERSION_HEX) && LIBMEMCACHED_VERSION_HEX < 0x01000018
Expand Down Expand Up @@ -4277,11 +4277,10 @@ static
PHP_GINIT_FUNCTION(php_memcached)
{
#ifdef HAVE_MEMCACHED_SESSION

php_memcached_globals->session.lock_enabled = 0;
php_memcached_globals->session.lock_wait_max = 150;
php_memcached_globals->session.lock_wait_min = 150;
php_memcached_globals->session.lock_retries = 200;
php_memcached_globals->session.lock_wait_max = 300;
php_memcached_globals->session.lock_retries = 5;
php_memcached_globals->session.lock_expiration = 30;
php_memcached_globals->session.binary_protocol_enabled = 1;
php_memcached_globals->session.consistent_hash_enabled = 1;
Expand All @@ -4296,8 +4295,8 @@ PHP_GINIT_FUNCTION(php_memcached)
php_memcached_globals->session.persistent_enabled = 0;
php_memcached_globals->session.sasl_username = NULL;
php_memcached_globals->session.sasl_password = NULL;

#endif

php_memcached_globals->memc.serializer_name = NULL;
php_memcached_globals->memc.serializer_type = SERIALIZER_DEFAULT;
php_memcached_globals->memc.compression_name = NULL;
Expand Down
13 changes: 11 additions & 2 deletions php_memcached_session.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include "php_memcached_session.h"

#include "Zend/zend_smart_str_public.h"
#include "ext/standard/php_mt_rand.h"

extern ZEND_DECLARE_MODULE_GLOBALS(php_memcached)

Expand Down Expand Up @@ -126,14 +127,22 @@ zend_bool s_lock_session(memcached_st *memc, zend_string *sid)
char *lock_key;
size_t lock_key_len;
time_t expiration;
zend_long wait_time, retries;
zend_long wait_time, wait_max, retries, perturb;
php_memcached_user_data *user_data = memcached_get_user_data(memc);

lock_key_len = spprintf(&lock_key, 0, "lock.%s", sid->val);
expiration = s_lock_expiration();

/* Implementation for a random exponential backoff:
* On the first retry, wait wait_min ms. On subsequent retries, wait
* for 20% longer than the previous retry, plus a random perturbation
* that is 10% of the difference between the minimum and maximum wait
* times. Never wait longer than the maximum wait time.
*/
wait_time = MEMC_SESS_INI(lock_wait_min);
wait_max = MEMC_SESS_INI(lock_wait_max);
retries = MEMC_SESS_INI(lock_retries);
perturb = php_mt_rand_range(0, MAX(wait_max, wait_time) - MIN(wait_max, wait_time)) / 10;

do {
rc = memcached_add(memc, lock_key, lock_key_len, "1", sizeof ("1") - 1, expiration, 0);
Expand All @@ -149,7 +158,7 @@ zend_bool s_lock_session(memcached_st *memc, zend_string *sid)
case MEMCACHED_DATA_EXISTS:
if (retries > 0) {
usleep(wait_time * 1000);
wait_time = MIN(MEMC_SESS_INI(lock_wait_max), wait_time * 2);
wait_time = MIN(wait_max, wait_time * 1.2 + perturb);
}
break;

Expand Down