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EP Parameters

1 Configuring the Engine

Engine parameters may be specified using the -e option to memcached. These parameters control various aspects of the behavior of the engine.

For example, if you would like to store your database in /data/base and prevent it from having objects larger than 1MB, you would run memcached like this:

memcached -E ep.so -e 'dbfile=/data/base;max_item_size=1048576'

2 Parameters for the EP Engine

keytypedescr
config_filestringPath to additional parameters.
dbnamestringPath to on-disk storage.
ht_locksintNumber of locks per hash table.
ht_sizeintNumber of buckets per hash table.
max_item_sizeintMaximum number of bytes allowed for
an item.
max_sizeintMax cumulative item size in bytes.
max_txn_sizeintMax number of disk mutations per
transaction.
mem_high_watintAutomatically evict when exceeding
this size.
mem_low_watintLow water mark to aim for when evicting.
min_data_ageintMinimum data stability time before
persist.
queue_age_capintMaximum queue time before forcing persist.
couch_response_timeoutintThe maximum time to wait for couch to
respond to a persistence request before
resetting the connection (milliseconds)
tap_backlog_limitintMax number of items allowed in a
tap backfill
tap_noop_intervalintNumber of seconds between a noop is sent
on an idle connection
tap_keepaliveintSeconds to hold open named tap connections
tap_bg_max_pendingintMaximum number of pending bg fetch
operations
a tap queue may issue (before it must wait
for responses to appear.
tap_backoff_periodfloatNumber of seconds the tap connection
should back off after receiving ETMPFAIL
vb0boolIf true, start with an active vbucket 0
waitforwarmupboolWhether to block server start during
warmup.
warmupboolWhether to load existing data at startup.
expiry_windowintexpiry window to not persist an object
that is expired (or will be soon)
exp_pager_stimeintSleep time for the pager that purges
expired objects from memory and disk
failpartialwarmupboolIf false, continue running after failing
to load some records.
max_vbucketsintMaximum number of vbuckets expected (1024)
concurrentDBboolTrue (default) if concurrent DB reads are
permitted where possible.
chk_remover_stimeintInterval for the checkpoint remover that
purges closed unreferenced checkpoints.
chk_max_itemsintNumber of max items allowed in a
checkpoint
chk_periodintTime bound (in sec.) on a checkpoint
max_checkpointsintNumber of max checkpoints allowed per
vbucket
inconsistent_slave_chkboolTrue if we allow a “downstream” master to
receive checkpoint begin/end messages
item_num_based_new_chkboolEnable a new checkpoint creation if the
number of items in a checkpoint is greater
than the max number allowed
along with normal get/set operations.
tap_backfill_residentfloatResident item threshold for only memory
backfill to be kicked off
keep_closed_chksboolTrue if we want to keep closed checkpoints
in memory if the current memory usage is
below high water mark
bf_resident_thresholdfloatResident item threshold for only memory
backfill to be kicked off
getl_default_timeoutintThe default timeout for a getl lock in (s)
getl_max_timeoutintThe maximum timeout for a getl lock in (s)
mutation_mem_thresholdfloatMemory threshold on the current bucket
quota for accepting a new mutation
tap_throttle_queue_capintThe maximum size of the disk write queue
to throttle down tap-based replication. -1
means don’t throttle.
tap_throttle_thresholdfloatPercentage of memory in use before we
throttle tap streams
tap_throttle_cap_pcntintPercentage of total items in write queue
to throttle tap input. 0 means use fixed
throttle queue cap.
klog_pathstringPath to the mutation key log.
klog_block_sizeintMutation key log block size.
klog_flushstringWhen to force buffer flushes during
klog (off, commit1, commit2, full)
klog_syncstringWhen to fsync during klog.
flushall_enabledboolTrue if we enable flush_all command; The
default value is False.
data_traffic_enabledboolTrue if we want to enable data traffic
immediately after warmup completion
alog_sleep_timeintInterval of access scanner task in (min)
alog_task_timeintHour (0~23) in GMT time at which access
}scanner will be scheduled to run.
pager_active_vb_pcntintPercentage of active vbucket items among
all evicted items by item pager.
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