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redis/src/expire.c

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/* Implementation of EXPIRE (keys with fixed time to live).
*
* ----------------------------------------------------------------------------
*
* Copyright (c) 2009-2016, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
#include "server.h"
/*-----------------------------------------------------------------------------
* Incremental collection of expired keys.
*
* When keys are accessed they are expired on-access. However we need a
* mechanism in order to ensure keys are eventually removed when expired even
* if no access is performed on them.
*----------------------------------------------------------------------------*/
/* Helper function for the activeExpireCycle() function.
* This function will try to expire the key that is stored in the hash table
* entry 'de' of the 'expires' hash table of a Redis database.
*
* If the key is found to be expired, it is removed from the database and
* 1 is returned. Otherwise no operation is performed and 0 is returned.
*
* When a key is expired, server.stat_expiredkeys is incremented.
*
* The parameter 'now' is the current time in milliseconds as is passed
* to the function to avoid too many gettimeofday() syscalls. */
int activeExpireCycleTryExpire(redisDb *db, dictEntry *de, long long now) {
long long t = dictGetSignedIntegerVal(de);
if (now > t) {
sds key = dictGetKey(de);
robj *keyobj = createStringObject(key,sdslen(key));
propagateExpire(db,keyobj,server.lazyfree_lazy_expire);
if (server.lazyfree_lazy_expire)
dbAsyncDelete(db,keyobj);
else
dbSyncDelete(db,keyobj);
notifyKeyspaceEvent(NOTIFY_EXPIRED,
"expired",keyobj,db->id);
decrRefCount(keyobj);
server.stat_expiredkeys++;
return 1;
} else {
return 0;
}
}
/* Try to expire a few timed out keys. The algorithm used is adaptive and
* will use few CPU cycles if there are few expiring keys, otherwise
* it will get more aggressive to avoid that too much memory is used by
* keys that can be removed from the keyspace.
*
* No more than CRON_DBS_PER_CALL databases are tested at every
* iteration.
*
* This kind of call is used when Redis detects that timelimit_exit is
* true, so there is more work to do, and we do it more incrementally from
* the beforeSleep() function of the event loop.
*
* Expire cycle type:
*
* If type is ACTIVE_EXPIRE_CYCLE_FAST the function will try to run a
* "fast" expire cycle that takes no longer than EXPIRE_FAST_CYCLE_DURATION
* microseconds, and is not repeated again before the same amount of time.
*
* If type is ACTIVE_EXPIRE_CYCLE_SLOW, that normal expire cycle is
* executed, where the time limit is a percentage of the REDIS_HZ period
* as specified by the ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC define. */
void activeExpireCycle(int type) {
/* This function has some global state in order to continue the work
* incrementally across calls. */
static unsigned int current_db = 0; /* Last DB tested. */
static int timelimit_exit = 0; /* Time limit hit in previous call? */
static long long last_fast_cycle = 0; /* When last fast cycle ran. */
int j, iteration = 0;
int dbs_per_call = CRON_DBS_PER_CALL;
long long start = ustime(), timelimit, elapsed;
/* When clients are paused the dataset should be static not just from the
* POV of clients not being able to write, but also from the POV of
* expires and evictions of keys not being performed. */
if (clientsArePaused()) return;
if (type == ACTIVE_EXPIRE_CYCLE_FAST) {
/* Don't start a fast cycle if the previous cycle did not exit
* for time limit. Also don't repeat a fast cycle for the same period
* as the fast cycle total duration itself. */
if (!timelimit_exit) return;
if (start < last_fast_cycle + ACTIVE_EXPIRE_CYCLE_FAST_DURATION*2) return;
last_fast_cycle = start;
}
/* We usually should test CRON_DBS_PER_CALL per iteration, with
* two exceptions:
*
* 1) Don't test more DBs than we have.
* 2) If last time we hit the time limit, we want to scan all DBs
* in this iteration, as there is work to do in some DB and we don't want
* expired keys to use memory for too much time. */
if (dbs_per_call > server.dbnum || timelimit_exit)
dbs_per_call = server.dbnum;
/* We can use at max ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC percentage of CPU time
* per iteration. Since this function gets called with a frequency of
* server.hz times per second, the following is the max amount of
* microseconds we can spend in this function. */
timelimit = 1000000*ACTIVE_EXPIRE_CYCLE_SLOW_TIME_PERC/server.hz/100;
timelimit_exit = 0;
if (timelimit <= 0) timelimit = 1;
if (type == ACTIVE_EXPIRE_CYCLE_FAST)
timelimit = ACTIVE_EXPIRE_CYCLE_FAST_DURATION; /* in microseconds. */
/* Accumulate some global stats as we expire keys, to have some idea
* about the number of keys that are already logically expired, but still
* existing inside the database. */
long total_sampled = 0;
long total_expired = 0;
for (j = 0; j < dbs_per_call && timelimit_exit == 0; j++) {
int expired;
redisDb *db = server.db+(current_db % server.dbnum);
/* Increment the DB now so we are sure if we run out of time
* in the current DB we'll restart from the next. This allows to
* distribute the time evenly across DBs. */
current_db++;
/* Continue to expire if at the end of the cycle more than 25%
* of the keys were expired. */
do {
unsigned long num, slots;
long long now, ttl_sum;
int ttl_samples;
iteration++;
/* If there is nothing to expire try next DB ASAP. */
if ((num = dictSize(db->expires)) == 0) {
db->avg_ttl = 0;
break;
}
slots = dictSlots(db->expires);
now = mstime();
/* When there are less than 1% filled slots getting random
* keys is expensive, so stop here waiting for better times...
* The dictionary will be resized asap. */
if (num && slots > DICT_HT_INITIAL_SIZE &&
(num*100/slots < 1)) break;
/* The main collection cycle. Sample random keys among keys
* with an expire set, checking for expired ones. */
expired = 0;
ttl_sum = 0;
ttl_samples = 0;
if (num > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP)
num = ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP;
while (num--) {
dictEntry *de;
long long ttl;
if ((de = dictGetRandomKey(db->expires)) == NULL) break;
ttl = dictGetSignedIntegerVal(de)-now;
if (activeExpireCycleTryExpire(db,de,now)) expired++;
if (ttl > 0) {
/* We want the average TTL of keys yet not expired. */
ttl_sum += ttl;
ttl_samples++;
}
total_sampled++;
}
total_expired += expired;
/* Update the average TTL stats for this database. */
if (ttl_samples) {
long long avg_ttl = ttl_sum/ttl_samples;
/* Do a simple running average with a few samples.
* We just use the current estimate with a weight of 2%
* and the previous estimate with a weight of 98%. */
if (db->avg_ttl == 0) db->avg_ttl = avg_ttl;
db->avg_ttl = (db->avg_ttl/50)*49 + (avg_ttl/50);
}
/* We can't block forever here even if there are many keys to
* expire. So after a given amount of milliseconds return to the
* caller waiting for the other active expire cycle. */
if ((iteration & 0xf) == 0) { /* check once every 16 iterations. */
elapsed = ustime()-start;
if (elapsed > timelimit) {
timelimit_exit = 1;
server.stat_expired_time_cap_reached_count++;
break;
}
}
/* We don't repeat the cycle if there are less than 25% of keys
* found expired in the current DB. */
} while (expired > ACTIVE_EXPIRE_CYCLE_LOOKUPS_PER_LOOP/4);
}
elapsed = ustime()-start;
latencyAddSampleIfNeeded("expire-cycle",elapsed/1000);
/* Update our estimate of keys existing but yet to be expired.
* Running average with this sample accounting for 5%. */
double current_perc;
if (total_sampled) {
current_perc = (double)total_expired/total_sampled;
} else
current_perc = 0;
server.stat_expired_stale_perc = (current_perc*0.05)+
(server.stat_expired_stale_perc*0.95);
}
/*-----------------------------------------------------------------------------
* Expires of keys created in writable slaves
*
* Normally slaves do not process expires: they wait the masters to synthesize
* DEL operations in order to retain consistency. However writable slaves are
* an exception: if a key is created in the slave and an expire is assigned
* to it, we need a way to expire such a key, since the master does not know
* anything about such a key.
*
* In order to do so, we track keys created in the slave side with an expire
* set, and call the expireSlaveKeys() function from time to time in order to
* reclaim the keys if they already expired.
*
* Note that the use case we are trying to cover here, is a popular one where
* slaves are put in writable mode in order to compute slow operations in
* the slave side that are mostly useful to actually read data in a more
* processed way. Think at sets intersections in a tmp key, with an expire so
* that it is also used as a cache to avoid intersecting every time.
*
* This implementation is currently not perfect but a lot better than leaking
* the keys as implemented in 3.2.
*----------------------------------------------------------------------------*/
/* The dictionary where we remember key names and database ID of keys we may
* want to expire from the slave. Since this function is not often used we
* don't even care to initialize the database at startup. We'll do it once
* the feature is used the first time, that is, when rememberSlaveKeyWithExpire()
* is called.
*
* The dictionary has an SDS string representing the key as the hash table
* key, while the value is a 64 bit unsigned integer with the bits corresponding
* to the DB where the keys may exist set to 1. Currently the keys created
* with a DB id > 63 are not expired, but a trivial fix is to set the bitmap
* to the max 64 bit unsigned value when we know there is a key with a DB
* ID greater than 63, and check all the configured DBs in such a case. */
dict *slaveKeysWithExpire = NULL;
/* Check the set of keys created by the master with an expire set in order to
* check if they should be evicted. */
void expireSlaveKeys(void) {
if (slaveKeysWithExpire == NULL ||
dictSize(slaveKeysWithExpire) == 0) return;
int cycles = 0, noexpire = 0;
mstime_t start = mstime();
while(1) {
dictEntry *de = dictGetRandomKey(slaveKeysWithExpire);
sds keyname = dictGetKey(de);
uint64_t dbids = dictGetUnsignedIntegerVal(de);
uint64_t new_dbids = 0;
/* Check the key against every database corresponding to the
* bits set in the value bitmap. */
int dbid = 0;
while(dbids && dbid < server.dbnum) {
if ((dbids & 1) != 0) {
redisDb *db = server.db+dbid;
dictEntry *expire = dictFind(db->expires,keyname);
int expired = 0;
if (expire &&
activeExpireCycleTryExpire(server.db+dbid,expire,start))
{
expired = 1;
}
/* If the key was not expired in this DB, we need to set the
* corresponding bit in the new bitmap we set as value.
* At the end of the loop if the bitmap is zero, it means we
* no longer need to keep track of this key. */
if (expire && !expired) {
noexpire++;
new_dbids |= (uint64_t)1 << dbid;
}
}
dbid++;
dbids >>= 1;
}
/* Set the new bitmap as value of the key, in the dictionary
* of keys with an expire set directly in the writable slave. Otherwise
* if the bitmap is zero, we no longer need to keep track of it. */
if (new_dbids)
dictSetUnsignedIntegerVal(de,new_dbids);
else
dictDelete(slaveKeysWithExpire,keyname);
/* Stop conditions: found 3 keys we can't expire in a row or
* time limit was reached. */
cycles++;
if (noexpire > 3) break;
if ((cycles % 64) == 0 && mstime()-start > 1) break;
if (dictSize(slaveKeysWithExpire) == 0) break;
}
}
/* Track keys that received an EXPIRE or similar command in the context
* of a writable slave. */
void rememberSlaveKeyWithExpire(redisDb *db, robj *key) {
if (slaveKeysWithExpire == NULL) {
static dictType dt = {
dictSdsHash, /* hash function */
NULL, /* key dup */
NULL, /* val dup */
dictSdsKeyCompare, /* key compare */
dictSdsDestructor, /* key destructor */
NULL /* val destructor */
};
slaveKeysWithExpire = dictCreate(&dt,NULL);
}
if (db->id > 63) return;
dictEntry *de = dictAddOrFind(slaveKeysWithExpire,key->ptr);
/* If the entry was just created, set it to a copy of the SDS string
* representing the key: we don't want to need to take those keys
* in sync with the main DB. The keys will be removed by expireSlaveKeys()
* as it scans to find keys to remove. */
if (de->key == key->ptr) {
de->key = sdsdup(key->ptr);
dictSetUnsignedIntegerVal(de,0);
}
uint64_t dbids = dictGetUnsignedIntegerVal(de);
dbids |= (uint64_t)1 << db->id;
dictSetUnsignedIntegerVal(de,dbids);
}
/* Return the number of keys we are tracking. */
size_t getSlaveKeyWithExpireCount(void) {
if (slaveKeysWithExpire == NULL) return 0;
return dictSize(slaveKeysWithExpire);
}
/* Remove the keys in the hash table. We need to do that when data is
* flushed from the server. We may receive new keys from the master with
* the same name/db and it is no longer a good idea to expire them.
*
* Note: technically we should handle the case of a single DB being flushed
* but it is not worth it since anyway race conditions using the same set
* of key names in a wriatable slave and in its master will lead to
* inconsistencies. This is just a best-effort thing we do. */
void flushSlaveKeysWithExpireList(void) {
if (slaveKeysWithExpire) {
dictRelease(slaveKeysWithExpire);
slaveKeysWithExpire = NULL;
}
}
/*-----------------------------------------------------------------------------
* Expires Commands
*----------------------------------------------------------------------------*/
/* This is the generic command implementation for EXPIRE, PEXPIRE, EXPIREAT
* and PEXPIREAT. Because the commad second argument may be relative or absolute
* the "basetime" argument is used to signal what the base time is (either 0
* for *AT variants of the command, or the current time for relative expires).
*
* unit is either UNIT_SECONDS or UNIT_MILLISECONDS, and is only used for
* the argv[2] parameter. The basetime is always specified in milliseconds. */
void expireGenericCommand(client *c, long long basetime, int unit) {
robj *key = c->argv[1], *param = c->argv[2];
long long when; /* unix time in milliseconds when the key will expire. */
if (getLongLongFromObjectOrReply(c, param, &when, NULL) != C_OK)
return;
if (unit == UNIT_SECONDS) when *= 1000;
when += basetime;
/* No key, return zero. */
if (lookupKeyWrite(c->db,key) == NULL) {
addReply(c,shared.czero);
return;
}
/* EXPIRE with negative TTL, or EXPIREAT with a timestamp into the past
* should never be executed as a DEL when load the AOF or in the context
* of a slave instance.
*
* Instead we take the other branch of the IF statement setting an expire
* (possibly in the past) and wait for an explicit DEL from the master. */
if (when <= mstime() && !server.loading && !server.masterhost) {
robj *aux;
int deleted = server.lazyfree_lazy_expire ? dbAsyncDelete(c->db,key) :
dbSyncDelete(c->db,key);
serverAssertWithInfo(c,key,deleted);
server.dirty++;
/* Replicate/AOF this as an explicit DEL or UNLINK. */
aux = server.lazyfree_lazy_expire ? shared.unlink : shared.del;
rewriteClientCommandVector(c,2,aux,key);
signalModifiedKey(c->db,key);
notifyKeyspaceEvent(NOTIFY_GENERIC,"del",key,c->db->id);
addReply(c, shared.cone);
return;
} else {
setExpire(c,c->db,key,when);
addReply(c,shared.cone);
signalModifiedKey(c->db,key);
notifyKeyspaceEvent(NOTIFY_GENERIC,"expire",key,c->db->id);
server.dirty++;
return;
}
}
/* EXPIRE key seconds */
void expireCommand(client *c) {
expireGenericCommand(c,mstime(),UNIT_SECONDS);
}
/* EXPIREAT key time */
void expireatCommand(client *c) {
expireGenericCommand(c,0,UNIT_SECONDS);
}
/* PEXPIRE key milliseconds */
void pexpireCommand(client *c) {
expireGenericCommand(c,mstime(),UNIT_MILLISECONDS);
}
/* PEXPIREAT key ms_time */
void pexpireatCommand(client *c) {
expireGenericCommand(c,0,UNIT_MILLISECONDS);
}
/* Implements TTL and PTTL */
void ttlGenericCommand(client *c, int output_ms) {
long long expire, ttl = -1;
/* If the key does not exist at all, return -2 */
if (lookupKeyReadWithFlags(c->db,c->argv[1],LOOKUP_NOTOUCH) == NULL) {
addReplyLongLong(c,-2);
return;
}
/* The key exists. Return -1 if it has no expire, or the actual
* TTL value otherwise. */
expire = getExpire(c->db,c->argv[1]);
if (expire != -1) {
ttl = expire-mstime();
if (ttl < 0) ttl = 0;
}
if (ttl == -1) {
addReplyLongLong(c,-1);
} else {
addReplyLongLong(c,output_ms ? ttl : ((ttl+500)/1000));
}
}
/* TTL key */
void ttlCommand(client *c) {
ttlGenericCommand(c, 0);
}
/* PTTL key */
void pttlCommand(client *c) {
ttlGenericCommand(c, 1);
}
/* PERSIST key */
void persistCommand(client *c) {
if (lookupKeyWrite(c->db,c->argv[1])) {
if (removeExpire(c->db,c->argv[1])) {
addReply(c,shared.cone);
server.dirty++;
} else {
addReply(c,shared.czero);
}
} else {
addReply(c,shared.czero);
}
}
/* TOUCH key1 [key2 key3 ... keyN] */
void touchCommand(client *c) {
int touched = 0;
for (int j = 1; j < c->argc; j++)
if (lookupKeyRead(c->db,c->argv[j]) != NULL) touched++;
addReplyLongLong(c,touched);
}
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