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|
/*-
* Copyright (c) 2014-2018 MongoDB, Inc.
* Copyright (c) 2008-2014 WiredTiger, Inc.
* All rights reserved.
*
* See the file LICENSE for redistribution information.
*/
#include "wt_internal.h"
/*
* Tuning constants.
*/
/*
* Threshold when a connection is allocated more cache, as a percentage of
* the amount of pressure the busiest participant has.
*/
#define WT_CACHE_POOL_BUMP_THRESHOLD 60
/*
* Threshold when a connection is allocated less cache, as a percentage of
* the amount of pressure the busiest participant has.
*/
#define WT_CACHE_POOL_REDUCE_THRESHOLD 20
/* Balancing passes after a bump before a connection is a candidate. */
#define WT_CACHE_POOL_BUMP_SKIPS 5
/* Balancing passes after a reduction before a connection is a candidate. */
#define WT_CACHE_POOL_REDUCE_SKIPS 10
/*
* Constants that control how much influence different metrics have on
* the pressure calculation.
*/
#define WT_CACHE_POOL_APP_EVICT_MULTIPLIER 3
#define WT_CACHE_POOL_APP_WAIT_MULTIPLIER 6
#define WT_CACHE_POOL_READ_MULTIPLIER 1
static void __cache_pool_adjust(
WT_SESSION_IMPL *, uint64_t, uint64_t, bool, bool *);
static void __cache_pool_assess(WT_SESSION_IMPL *, uint64_t *);
static void __cache_pool_balance(WT_SESSION_IMPL *, bool);
/*
* __wt_cache_pool_config --
* Parse and setup the cache pool options.
*/
int
__wt_cache_pool_config(WT_SESSION_IMPL *session, const char **cfg)
{
WT_CACHE_POOL *cp;
WT_CONFIG_ITEM cval, cval_cache_size;
WT_CONNECTION_IMPL *conn, *entry;
WT_DECL_RET;
uint64_t chunk, quota, reserve, size, used_cache;
char *pool_name;
bool created, updating;
conn = S2C(session);
created = updating = false;
pool_name = NULL;
cp = NULL;
if (F_ISSET(conn, WT_CONN_CACHE_POOL))
updating = true;
else {
WT_RET(__wt_config_gets_none(
session, cfg, "shared_cache.name", &cval));
if (cval.len == 0) {
/*
* Tell the user if they configured a cache pool
* size but didn't enable it by naming the pool.
*/
if (__wt_config_gets(session, &cfg[1],
"shared_cache.size", &cval) != WT_NOTFOUND)
WT_RET_MSG(session, EINVAL,
"Shared cache configuration requires a "
"pool name");
return (0);
}
if (__wt_config_gets(session,
&cfg[1], "cache_size", &cval_cache_size) != WT_NOTFOUND)
WT_RET_MSG(session, EINVAL,
"Only one of cache_size and shared_cache can be "
"in the configuration");
/*
* NOTE: The allocations made when configuring and opening a
* cache pool don't really belong to the connection that
* allocates them. If a memory allocator becomes connection
* specific in the future we will need a way to allocate memory
* outside of the connection here.
*/
WT_RET(__wt_strndup(session, cval.str, cval.len, &pool_name));
}
__wt_spin_lock(session, &__wt_process.spinlock);
if (__wt_process.cache_pool == NULL) {
WT_ASSERT(session, !updating);
/* Create a cache pool. */
WT_ERR(__wt_calloc_one(session, &cp));
created = true;
cp->name = pool_name;
pool_name = NULL; /* Belongs to the cache pool now. */
TAILQ_INIT(&cp->cache_pool_qh);
WT_ERR(__wt_spin_init(
session, &cp->cache_pool_lock, "cache shared pool"));
WT_ERR(__wt_cond_alloc(
session, "cache pool server", &cp->cache_pool_cond));
__wt_process.cache_pool = cp;
__wt_verbose(session,
WT_VERB_SHARED_CACHE, "Created cache pool %s", cp->name);
} else if (!updating &&
strcmp(__wt_process.cache_pool->name, pool_name) != 0)
/* Only a single cache pool is supported. */
WT_ERR_MSG(session, WT_ERROR,
"Attempting to join a cache pool that does not exist: %s",
pool_name);
cp = __wt_process.cache_pool;
/*
* The cache pool requires a reference count to avoid a race between
* configuration/open and destroy.
*/
if (!updating)
++cp->refs;
/*
* Cache pool configurations are optional when not creating. If
* values aren't being changed, retrieve the current value so that
* validation of settings works.
*/
if (!created) {
if (__wt_config_gets(session, &cfg[1],
"shared_cache.size", &cval) == 0 && cval.val != 0)
size = (uint64_t)cval.val;
else
size = cp->size;
if (__wt_config_gets(session, &cfg[1],
"shared_cache.chunk", &cval) == 0 && cval.val != 0)
chunk = (uint64_t)cval.val;
else
chunk = cp->chunk;
if (__wt_config_gets(session, &cfg[1],
"shared_cache.quota", &cval) == 0 && cval.val != 0)
quota = (uint64_t)cval.val;
else
quota = cp->quota;
} else {
/*
* The only time shared cache configuration uses default
* values is when we are creating the pool.
*/
WT_ERR(__wt_config_gets(
session, cfg, "shared_cache.size", &cval));
WT_ASSERT(session, cval.val != 0);
size = (uint64_t)cval.val;
WT_ERR(__wt_config_gets(
session, cfg, "shared_cache.chunk", &cval));
WT_ASSERT(session, cval.val != 0);
chunk = (uint64_t)cval.val;
WT_ERR(__wt_config_gets(
session, cfg, "shared_cache.quota", &cval));
quota = (uint64_t)cval.val;
}
/*
* Retrieve the reserve size here for validation of configuration.
* Don't save it yet since the connections cache is not created if
* we are opening. Cache configuration is responsible for saving the
* setting.
* The different conditions when reserved size are set are:
* - It's part of the users configuration - use that value.
* - We are reconfiguring - keep the previous value.
* - We are joining a cache pool for the first time (including
* creating the pool) - use the chunk size; that's the default.
*/
if (__wt_config_gets(session, &cfg[1],
"shared_cache.reserve", &cval) == 0 && cval.val != 0)
reserve = (uint64_t)cval.val;
else if (updating)
reserve = conn->cache->cp_reserved;
else
reserve = chunk;
/*
* Validate that size and reserve values don't cause the cache
* pool to be over subscribed.
*/
used_cache = 0;
if (!created) {
TAILQ_FOREACH(entry, &cp->cache_pool_qh, cpq)
used_cache += entry->cache->cp_reserved;
}
/* Ignore our old allocation if reconfiguring */
if (updating)
used_cache -= conn->cache->cp_reserved;
if (used_cache + reserve > size)
WT_ERR_MSG(session, EINVAL,
"Shared cache unable to accommodate this configuration. "
"Shared cache size: %" PRIu64 ", requested min: %" PRIu64,
size, used_cache + reserve);
/* The configuration is verified - it's safe to update the pool. */
cp->size = size;
cp->chunk = chunk;
cp->quota = quota;
conn->cache->cp_reserved = reserve;
conn->cache->cp_quota = quota;
/* Wake up the cache pool server so any changes are noticed. */
if (updating)
__wt_cond_signal(
session, __wt_process.cache_pool->cache_pool_cond);
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Configured cache pool %s. Size: %" PRIu64
", chunk size: %" PRIu64, cp->name, cp->size, cp->chunk);
F_SET(conn, WT_CONN_CACHE_POOL);
err: __wt_spin_unlock(session, &__wt_process.spinlock);
__wt_free(session, pool_name);
if (ret != 0 && created) {
__wt_free(session, cp->name);
__wt_cond_destroy(session, &cp->cache_pool_cond);
__wt_free(session, cp);
}
return (ret);
}
/*
* __wt_conn_cache_pool_open --
* Add a connection to the cache pool.
*/
int
__wt_conn_cache_pool_open(WT_SESSION_IMPL *session)
{
WT_CACHE *cache;
WT_CACHE_POOL *cp;
WT_CONNECTION_IMPL *conn;
WT_DECL_RET;
uint32_t session_flags;
conn = S2C(session);
cache = conn->cache;
cp = __wt_process.cache_pool;
/*
* Create a session that can be used by the cache pool thread, do
* it in the main thread to avoid shutdown races
*/
session_flags = WT_SESSION_NO_DATA_HANDLES;
if ((ret = __wt_open_internal_session(
conn, "cache-pool", false, session_flags, &cache->cp_session)) != 0)
WT_RET_MSG(NULL, ret,
"Failed to create session for cache pool");
/*
* Add this connection into the cache pool connection queue. Figure
* out if a manager thread is needed while holding the lock. Don't
* start the thread until we have released the lock.
*/
__wt_spin_lock(session, &cp->cache_pool_lock);
TAILQ_INSERT_TAIL(&cp->cache_pool_qh, conn, cpq);
__wt_spin_unlock(session, &cp->cache_pool_lock);
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Added %s to cache pool %s", conn->home, cp->name);
/*
* Each connection participating in the cache pool starts a manager
* thread. Only one manager is active at a time, but having a thread
* in each connection saves having a complex election process when
* the active connection shuts down.
*/
F_SET(cp, WT_CACHE_POOL_ACTIVE);
FLD_SET(cache->pool_flags, WT_CACHE_POOL_RUN);
WT_RET(__wt_thread_create(session, &cache->cp_tid,
__wt_cache_pool_server, cache->cp_session));
/* Wake up the cache pool server to get our initial chunk. */
__wt_cond_signal(session, cp->cache_pool_cond);
return (0);
}
/*
* __wt_conn_cache_pool_destroy --
* Remove our resources from the shared cache pool. Remove the cache pool
* if we were the last connection.
*/
int
__wt_conn_cache_pool_destroy(WT_SESSION_IMPL *session)
{
WT_CACHE *cache;
WT_CACHE_POOL *cp;
WT_CONNECTION_IMPL *conn, *entry;
WT_DECL_RET;
WT_SESSION *wt_session;
bool cp_locked, found;
conn = S2C(session);
cache = conn->cache;
WT_NOT_READ(cp_locked, false);
found = false;
cp = __wt_process.cache_pool;
if (!F_ISSET(conn, WT_CONN_CACHE_POOL))
return (0);
F_CLR(conn, WT_CONN_CACHE_POOL);
__wt_spin_lock(session, &cp->cache_pool_lock);
cp_locked = true;
TAILQ_FOREACH(entry, &cp->cache_pool_qh, cpq)
if (entry == conn) {
found = true;
break;
}
/*
* If there was an error during open, we may not have made it onto the
* queue. We did increment the reference count, so proceed regardless.
*/
if (found) {
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Removing %s from cache pool", entry->home);
TAILQ_REMOVE(&cp->cache_pool_qh, entry, cpq);
/* Give the connection's resources back to the pool. */
WT_ASSERT(session, cp->currently_used >= conn->cache_size);
cp->currently_used -= conn->cache_size;
/*
* Stop our manager thread - release the cache pool lock while
* joining the thread to allow it to complete any balance
* operation.
*/
__wt_spin_unlock(session, &cp->cache_pool_lock);
WT_NOT_READ(cp_locked, false);
FLD_CLR(cache->pool_flags, WT_CACHE_POOL_RUN);
__wt_cond_signal(session, cp->cache_pool_cond);
WT_TRET(__wt_thread_join(session, &cache->cp_tid));
wt_session = &cache->cp_session->iface;
WT_TRET(wt_session->close(wt_session, NULL));
/*
* Grab the lock again now to stop other threads joining the
* pool while we are figuring out whether we were the last
* participant.
*/
__wt_spin_lock(session, &cp->cache_pool_lock);
cp_locked = true;
}
/*
* If there are no references, we are cleaning up after a failed
* wiredtiger_open, there is nothing further to do.
*/
if (cp->refs < 1) {
if (cp_locked)
__wt_spin_unlock(session, &cp->cache_pool_lock);
return (0);
}
if (--cp->refs == 0) {
WT_ASSERT(session, TAILQ_EMPTY(&cp->cache_pool_qh));
F_CLR(cp, WT_CACHE_POOL_ACTIVE);
}
if (!F_ISSET(cp, WT_CACHE_POOL_ACTIVE)) {
__wt_verbose(session,
WT_VERB_SHARED_CACHE, "%s", "Destroying cache pool");
__wt_spin_lock(session, &__wt_process.spinlock);
/*
* We have been holding the pool lock - no connections could
* have been added.
*/
WT_ASSERT(session,
cp == __wt_process.cache_pool &&
TAILQ_EMPTY(&cp->cache_pool_qh));
__wt_process.cache_pool = NULL;
__wt_spin_unlock(session, &__wt_process.spinlock);
__wt_spin_unlock(session, &cp->cache_pool_lock);
cp_locked = false;
/* Now free the pool. */
__wt_free(session, cp->name);
__wt_spin_destroy(session, &cp->cache_pool_lock);
__wt_cond_destroy(session, &cp->cache_pool_cond);
__wt_free(session, cp);
}
if (cp_locked) {
__wt_spin_unlock(session, &cp->cache_pool_lock);
/* Notify other participants if we were managing */
if (FLD_ISSET(cache->pool_flags, WT_CACHE_POOL_MANAGER)) {
cp->pool_managed = 0;
__wt_verbose(session, WT_VERB_SHARED_CACHE, "%s",
"Shutting down shared cache manager connection");
}
}
return (ret);
}
/*
* __cache_pool_balance --
* Do a pass over the cache pool members and ensure the pool is being
* effectively used.
*/
static void
__cache_pool_balance(WT_SESSION_IMPL *session, bool forward)
{
WT_CACHE_POOL *cp;
uint64_t bump_threshold, highest;
int i;
bool adjusted;
cp = __wt_process.cache_pool;
adjusted = false;
highest = 0;
__wt_spin_lock(NULL, &cp->cache_pool_lock);
/* If the queue is empty there is nothing to do. */
if (TAILQ_FIRST(&cp->cache_pool_qh) == NULL) {
__wt_spin_unlock(NULL, &cp->cache_pool_lock);
return;
}
__cache_pool_assess(session, &highest);
bump_threshold = WT_CACHE_POOL_BUMP_THRESHOLD;
/*
* Actively attempt to:
* - Reduce the amount allocated, if we are over the budget.
* - Increase the amount used if there is capacity and any pressure.
* Don't keep trying indefinitely, if we aren't succeeding in reducing
* the cache in use re-assessing the participants' states is necessary.
* We are also holding a lock across this process, which can slow
* participant shutdown if we spend a long time balancing.
*/
for (i = 0;
i < 2 * WT_CACHE_POOL_BUMP_THRESHOLD &&
F_ISSET(cp, WT_CACHE_POOL_ACTIVE) &&
FLD_ISSET(S2C(session)->cache->pool_flags, WT_CACHE_POOL_RUN);
i++) {
__cache_pool_adjust(
session, highest, bump_threshold, forward, &adjusted);
/*
* Stop if the amount of cache being used is stable, and we
* aren't over capacity.
*/
if (cp->currently_used <= cp->size && !adjusted)
break;
if (bump_threshold > 0)
--bump_threshold;
}
__wt_spin_unlock(NULL, &cp->cache_pool_lock);
}
/*
* __cache_pool_assess --
* Assess the usage of the cache pool.
*/
static void
__cache_pool_assess(WT_SESSION_IMPL *session, uint64_t *phighest)
{
WT_CACHE *cache;
WT_CACHE_POOL *cp;
WT_CONNECTION_IMPL *entry;
uint64_t app_evicts, app_waits, reads;
uint64_t balanced_size, entries, highest, tmp;
cp = __wt_process.cache_pool;
balanced_size = entries = 0;
highest = 1; /* Avoid divide by zero */
TAILQ_FOREACH(entry, &cp->cache_pool_qh, cpq) {
if (entry->cache_size == 0 || entry->cache == NULL)
continue;
++entries;
}
if (entries > 0)
balanced_size = cp->currently_used / entries;
/* Generate read pressure information. */
TAILQ_FOREACH(entry, &cp->cache_pool_qh, cpq) {
if (entry->cache_size == 0 || entry->cache == NULL)
continue;
cache = entry->cache;
/*
* Figure out a delta since the last time we did an assessment
* for each metric we are tracking. Watch out for wrapping
* of values.
*
* Count pages read, assuming pages are 4KB.
*/
tmp = cache->bytes_read >> 12;
if (tmp >= cache->cp_saved_read)
reads = tmp - cache->cp_saved_read;
else
reads = tmp;
cache->cp_saved_read = tmp;
/* Update the application eviction count information */
tmp = cache->app_evicts;
if (tmp >= cache->cp_saved_app_evicts)
app_evicts = tmp - cache->cp_saved_app_evicts;
else
app_evicts =
(UINT64_MAX - cache->cp_saved_app_evicts) + tmp;
cache->cp_saved_app_evicts = tmp;
/* Update the eviction wait information */
tmp = cache->app_waits;
if (tmp >= cache->cp_saved_app_waits)
app_waits = tmp - cache->cp_saved_app_waits;
else
app_waits =
(UINT64_MAX - cache->cp_saved_app_waits) + tmp;
cache->cp_saved_app_waits = tmp;
/* Calculate the weighted pressure for this member. */
tmp = (app_evicts * WT_CACHE_POOL_APP_EVICT_MULTIPLIER) +
(app_waits * WT_CACHE_POOL_APP_WAIT_MULTIPLIER) +
(reads * WT_CACHE_POOL_READ_MULTIPLIER);
/* Weight smaller caches higher. */
tmp = (uint64_t)(tmp *
((double)balanced_size / entry->cache_size));
/* Smooth over history. */
cache->cp_pass_pressure =
(9 * cache->cp_pass_pressure + tmp) / 10;
if (cache->cp_pass_pressure > highest)
highest = cache->cp_pass_pressure;
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Assess entry. reads: %" PRIu64 ", app evicts: %" PRIu64
", app waits: %" PRIu64 ", pressure: %" PRIu64,
reads, app_evicts, app_waits, cache->cp_pass_pressure);
}
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Highest eviction count: %" PRIu64 ", entries: %" PRIu64,
highest, entries);
*phighest = highest;
}
/*
* __cache_pool_adjust --
* Adjust the allocation of cache to each connection. If full is set
* ignore cache load information, and reduce the allocation for every
* connection allocated more than their reserved size.
*/
static void
__cache_pool_adjust(WT_SESSION_IMPL *session,
uint64_t highest, uint64_t bump_threshold, bool forward, bool *adjustedp)
{
WT_CACHE *cache;
WT_CACHE_POOL *cp;
WT_CONNECTION_IMPL *entry;
double pct_full;
uint64_t adjustment, highest_percentile, pressure, reserved, smallest;
bool busy, decrease_ok, grow, pool_full;
*adjustedp = false;
cp = __wt_process.cache_pool;
grow = false;
pool_full = cp->currently_used >= cp->size;
pct_full = 0.0;
/* Highest as a percentage, avoid 0 */
highest_percentile = (highest / 100) + 1;
if (WT_VERBOSE_ISSET(session, WT_VERB_SHARED_CACHE)) {
__wt_verbose(session,
WT_VERB_SHARED_CACHE, "%s", "Cache pool distribution: ");
__wt_verbose(session, WT_VERB_SHARED_CACHE, "%s",
"\t" "cache (MB), pressure, skips, busy, %% full:");
}
for (entry = forward ? TAILQ_FIRST(&cp->cache_pool_qh) :
TAILQ_LAST(&cp->cache_pool_qh, __wt_cache_pool_qh);
entry != NULL;
entry = forward ? TAILQ_NEXT(entry, cpq) :
TAILQ_PREV(entry, __wt_cache_pool_qh, cpq)) {
cache = entry->cache;
reserved = cache->cp_reserved;
adjustment = 0;
/*
* The read pressure is calculated as a percentage of how
* much read pressure there is on this participant compared
* to the participant with the most activity. The closer we
* are to the most active the more cache we should get
* assigned.
*/
pressure = cache->cp_pass_pressure / highest_percentile;
busy = __wt_eviction_needed(
entry->default_session, false, true, &pct_full);
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"\t%5" PRIu64 ", %3" PRIu64 ", %2" PRIu32 ", %d, %2.3f",
entry->cache_size >> 20, pressure, cache->cp_skip_count,
busy, pct_full);
/* Allow to stabilize after changes. */
if (cache->cp_skip_count > 0 && --cache->cp_skip_count > 0)
continue;
/*
* The bump threshold decreases as we try longer to balance
* the pool. Adjust how aggressively we free space from
* participants depending on how long we have been trying.
*/
decrease_ok = false;
/*
* Any participant is a candidate if we have been trying
* for long enough.
*/
if (bump_threshold == 0)
decrease_ok = true;
/*
* Participants that aren't doing application eviction and
* are showing a reasonable amount of usage are excluded
* even if we have been trying for a while.
*/
else if (bump_threshold < WT_CACHE_POOL_BUMP_THRESHOLD / 3 &&
(!busy && highest > 1))
decrease_ok = true;
/*
* Any participant that is proportionally less busy is a
* candidate from the first attempt.
*/
else if (highest > 1 &&
pressure < WT_CACHE_POOL_REDUCE_THRESHOLD)
decrease_ok = true;
/*
* If the entry is currently allocated less than the reserved
* size, increase its allocation. This should only happen if:
* - it's the first time we've seen this member, or
* - the reserved size has been adjusted
*/
if (entry->cache_size < reserved) {
grow = true;
adjustment = reserved - entry->cache_size;
/*
* Conditions for reducing the amount of resources for an
* entry:
* - the pool is full,
* - this entry has more than the minimum amount of space in
* use,
* - it was determined that this slot is a good candidate
*/
} else if (pool_full &&
entry->cache_size > reserved && decrease_ok) {
grow = false;
/*
* Don't drop the size down too much - or it can
* trigger aggressive eviction in the connection,
* which is likely to lead to lower throughput and
* potentially a negative feedback loop in the
* balance algorithm.
*/
smallest =
(uint64_t)((100 * __wt_cache_bytes_inuse(cache)) /
cache->eviction_trigger);
if (entry->cache_size > smallest)
adjustment = WT_MIN(cp->chunk,
(entry->cache_size - smallest) / 2);
adjustment =
WT_MIN(adjustment, entry->cache_size - reserved);
/*
* Conditions for increasing the amount of resources for an
* entry:
* - there is space available in the pool
* - the connection isn't over quota
* - the connection is using enough cache to require eviction
* - there was some activity across the pool
* - this entry is using less than the entire cache pool
* - additional cache would benefit the connection OR
* - the pool is less than half distributed
*/
} else if (!pool_full &&
(cache->cp_quota == 0 ||
entry->cache_size < cache->cp_quota) &&
__wt_cache_bytes_inuse(cache) >=
(entry->cache_size * cache->eviction_target) / 100 &&
(pressure > bump_threshold ||
cp->currently_used < cp->size * 0.5)) {
grow = true;
adjustment = WT_MIN(WT_MIN(cp->chunk,
cp->size - cp->currently_used),
cache->cp_quota - entry->cache_size);
}
/*
* Bounds checking: don't go over the pool size or under the
* reserved size for this cache.
*
* Shrink by a chunk size if that doesn't drop us
* below the reserved size.
*
* Limit the reduction to half of the free space in the
* connection's cache. This should reduce cache sizes
* gradually without stalling application threads.
*/
if (adjustment > 0) {
*adjustedp = true;
if (grow) {
cache->cp_skip_count = WT_CACHE_POOL_BUMP_SKIPS;
entry->cache_size += adjustment;
cp->currently_used += adjustment;
} else {
cache->cp_skip_count =
WT_CACHE_POOL_REDUCE_SKIPS;
WT_ASSERT(session,
entry->cache_size >= adjustment &&
cp->currently_used >= adjustment);
entry->cache_size -= adjustment;
cp->currently_used -= adjustment;
}
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"Allocated %s%" PRIu64 " to %s",
grow ? "" : "-", adjustment, entry->home);
/*
* TODO: Add a loop waiting for connection to give up
* cache.
*/
}
}
}
/*
* __wt_cache_pool_server --
* Thread to manage cache pool among connections.
*/
WT_THREAD_RET
__wt_cache_pool_server(void *arg)
{
WT_CACHE *cache;
WT_CACHE_POOL *cp;
WT_SESSION_IMPL *session;
bool forward;
session = (WT_SESSION_IMPL *)arg;
cp = __wt_process.cache_pool;
cache = S2C(session)->cache;
forward = true;
while (F_ISSET(cp, WT_CACHE_POOL_ACTIVE) &&
FLD_ISSET(cache->pool_flags, WT_CACHE_POOL_RUN)) {
if (cp->currently_used <= cp->size)
__wt_cond_wait(
session, cp->cache_pool_cond, WT_MILLION, NULL);
/*
* Re-check pool run flag - since we want to avoid getting the
* lock on shutdown.
*/
if (!F_ISSET(cp, WT_CACHE_POOL_ACTIVE) &&
FLD_ISSET(cache->pool_flags, WT_CACHE_POOL_RUN))
break;
/* Try to become the managing thread */
if (__wt_atomic_cas8(&cp->pool_managed, 0, 1)) {
FLD_SET(cache->pool_flags, WT_CACHE_POOL_MANAGER);
__wt_verbose(session, WT_VERB_SHARED_CACHE,
"%s", "Cache pool switched manager thread");
}
/*
* Continue even if there was an error. Details of errors are
* reported in the balance function.
*/
if (FLD_ISSET(cache->pool_flags, WT_CACHE_POOL_MANAGER)) {
__cache_pool_balance(session, forward);
forward = !forward;
}
}
return (WT_THREAD_RET_VALUE);
}
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