Database Compaction#

Because CouchDb/BigCouch uses an append-only file to write changes to, you must monitor the size of those files on disk and periodically compact them. Compaction is the process of taking all the current revisions in the file and writing a new file with just the active documents, effectively deleting all old revisions. Compaction can have dramatic results in recovered disk space and performance (as seek times are reduced on smaller files).

Automatic Compaction#

Kazoo allows the cluster operator to enable automatic compaction of all databases. A process will walk the list of known databases (updating each time the process starts again) and check each database against a heuristic to decide whether to compact or not.

System Configuration Schema#

Schema for kazoo_couch system_config

Key Description Type Default Required
admin_port The CouchDB API port, typically 5986 integer false
allow_maintenance_db_delete kazoo_couch allow maintenance db delete boolean false false
api_port The CouchDB API port, typically 5984 integer 5984 false
autocompaction_check kazoo_couch autocompaction check integer 60000 false
bigcouch_cookie The cookie value of all the BigCouch nodes string false
compact_automatically kazoo_couch compact automatically boolean true false
default_chunk_size kazoo_couch default chunk size integer 1000 false
max_compacting_shards kazoo_couch maximum compacting shards integer 2 false
max_compacting_views kazoo_couch maximum compacting views integer 2 false
max_concurrent_docs_to_archive kazoo_couch maximum concurrent docs to archive integer 500 false
max_wait_for_compaction_pids kazoo_couch maximum wait for compaction pids integer 360000 false
min_data_size kazoo_couch minimum data size integer 131072 false
min_ratio kazoo_couch minimum ratio number 1.2 false
sleep_between_compaction kazoo_couch sleep between compaction integer 60000 false
sleep_between_poll kazoo_couch sleep between poll integer 3000 false
sleep_between_views kazoo_couch sleep between views integer 2000 false
use_bigcouch_direct kazoo_couch use bigcouch direct boolean true false

Operations#

The compaction module (kt_compactor)[../src/modules/kt_compactor.erl] binds into the triggers for all databases. Based on the tasks.browse_dbs_interval_s in system_config, each database will be processed each time the timer expires. The default timeout is daily, but the next timer won't start until all the databases have been processed by all task modules bound for them. On large systems, there could be so many databases and operations could take a long time on them, that the next timer won't start for more than a day.

Typically there's nothing wrong with that, just know that the timer isn't a daily timer but instead is 84600 seconds after the last database is processed.

Per-node settings#

Its important to set per-couch-node settings if your setup varies from the default ports (5984 and 5986).

sup kapps_config set_node kazoo_couch admin_port 35986 couchdb@db001.host.com

Repeat for admin_port and api_port for each database node in your setup (curl localhost:5984/_membership if you need your list of nodes).

API-initiated compaction#

In addition to the automatic crawling of databases available, the tasks API contains methods for initiating compaction of the cluster, per-node, or per-database.

Compact Everything#

This is an input-less compaction job. At the end of the run, you should have a CSV with output about the database shards on each node with their disk/data usage before and after compaction.

  1. Create the task: shell curl -v -X PUT \ -H "X-Auth-Token: {AUTH_TOKEN}" \ 'http://{SERVER}:8000/v2/tasks?category=compaction&action=compact_all'

  2. Start the task: shell curl -v -X PATCH \ -H "X-Auth-Token: {AUTH_TOKEN}" \ 'http://{SERVER}:8000/v2/tasks/{TASK_ID}'

  3. Query the task's status: shell curl -v -X GET \ -H "X-Auth-Token: {AUTH_TOKEN}" \ 'http://{SERVER}:8000/v2/tasks/{TASK_ID}'

  4. Export the results shell curl -v -X GET \ -o compaction_results.csv -H "Accept: text/csv" -H "X-Auth-Token: $AUTH_TOKEN" 'http://{SERVER}:8000/v2/tasks/{TASK_ID}?csv_name=out.csv' csv node,database,before_disk,before_data,after_disk,after_data node3@127.0.0.1,faxes,804116,1544,804116,1544 node2@127.0.0.1,faxes,554260,1544,1230100,1544 node1@127.0.0.1,faxes,132372,1544,132372,1544

Compact a node#

If you prefer, you can specify a CSV with nodes to compact, including a flag to force compaction or use the heuristics to do it.

CSV columns#

| Column | Description | | node | Which node(s) to run compaction on | | force | Whether to force compaction on each database or apply the ratio heuristic |

For instance, compact two nodes, forcing all databases to be compacted on the first node, and only those meeting the ratio criteria on the second node:

"node","force"
"bigcouch@db001.zone1.host.com","true"
"bigcouch@db004.zone3.host.co.uk","false"

API commands#

Create the task: shell curl -v -X PUT \ -H "X-Auth-Token: $AUTH_TOKEN" \ -H "Content-Type: text/csv" \ 'http://localhost:8000/v2/tasks?category=compaction&action=compact_node' \ --data-binary $'"node","force"\n"node1@127.0.0.1","false"\n"node2@127.0.0.1","true"'

Note: if you want to specify the CSV content in the args to cURL, you need to use $'...' to allow the \n to be passed to Crossbar properly. Otherwise create a CSV file and use @file.csv instead.

Start, query, and export the results as before.

Compact a database#

Compacting a database will ensure all shards on relevant nodes are compacted.

CSV columns#

| Column | Description | | database | Which database to run compaction on | | force | Whether to force compaction on the database or apply the ratio heuristic |

For instance, compact two databases, forcing compaction on the first database, and apply the ratio heuristic to see if the second database should be compacted.

"database","force"
"system_config","true"
"accounts","false"

API commands#

  1. Create the task: shell curl -v -X PUT \ -H "X-Auth-Token: {AUTH_TOKEN}" \ -H "Content-Type: application/json" \ --data-binary @/path/to/node.csv 'http://{SERVER}:8000/v2/tasks?category=compaction&action=compact_db'

Start, query and export as before.

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