The disk write queues quota impacts the rate of data sent from source nodes to destination nodes.
The basic syntax is:
cbepctl [host]:11210 -b [bucket-name] -p [bucket-password] set tap_param [parameter] [value] cbepctl [host]:11210 -b [bucket-name] -p [bucket-password] set tap_param tap_throttle_queue_cap [value] cbepctl [host]:11210 -b [bucket-name] -p [bucket-password] set tap_param tap_throttle_cap_pcnt [value]
One of the specific uses of the command set tap_param is to change the default maximum items for a disk write queue. This impacts replication of data that occurs between source and destination nodes within a cluster. Both data that a node receives from client applications and replicated items that it receives are placed on a disk write queue. If there are too many items waiting in the disk write queue at any given destination, Couchbase Server reduces the rate of data that is sent to a destination. This process is also known as backoff.
By default, when a disk write queue contains one million items a Couchbase Server node reduces the rate it sends out data to be replicated. This setting can be changed to be the greater of 10% of the items at a destination node or a specific number.
The following are the command options:
|tap_keepalive||Seconds to hold a named tap connection.|
|tap_throttle_queue_cap||The maximum disk write queue size when tap streams are put into a temporary 5-second pause. Infinite means there is no cap.|
|tap_throttle_cap_pcnt||The maximum number of items in the disk write queue as a percentage of all items on a node. At this point, tap streams are put into a temporary, 5-second pause.|
|tap_throttle_threshold||Percentage of memory in use when tap streams are put into a temporary, 5-second pause.|
Change the default bucket setting to specify that a replica node sends a request for backoff when it has two million items.
cbepctl 10.5.2.117:11210 set tap_param tap_throttle_queue_cap 2000000
The following example for the default bucket changes the default percentage used to manage the replication stream. If the items in a disk write queue reach the greater of this percentage or a specified number of items, replication requests slow down.
The threshold is set to 15% of all items at a replica node. When a disk write queue on a replica node reaches this point, it requests replication backoff.
cbepctl 10.5.2.117:11210 set tap_param tap_throttle_cap_pcnt 15
The following example responses show a two million setting and a 15% threshold:
setting param: tap_throttle_queue_cap 2000000 set tap_throttle_queue_cap to 2000000 setting param: tap_throttle_cap_pcnt 15 set tap_throttle_cap_pcnt to 15