# 3.2. Base Configuration

## 3.2.1. Base CouchDB Options

`[couchdb]`

  > `attachment_stream_buffer_size`

  >   Higher values may result in better read performance due to fewer read operations and/or more OS page cache hits. However, they can also increase overall response time for writes when there are many attachment write requests in parallel.

  >       [couchdb]
  >       attachment_stream_buffer_size = 4096

  > `database_dir`

  >   Specifies location of CouchDB database files (`*.couch` named). This location should be writable and readable for the user the CouchDB service runs as (`couchdb` by default).

  >       [couchdb]
  >       database_dir = /var/lib/couchdb

  > `delayed_commits`

  >   When this config value is `false` the CouchDB provides a guarantee that fsync will be called before returning a 201 Created response on each document save. Setting this config value to `true` may improve performance, at cost of some durability. For production use disabling this is strongly recommended:

  >       [couchdb]
  >       delayed_commits = false

  >   Warning

  >   Delayed commits are a feature of CouchDB that allows it to achieve better write performance for some workloads while sacrificing a small amount of durability. The setting causes CouchDB to wait up to a full second before committing new data after an update. If the server crashes before the header is written then any writes since the last commit are lost.

  > `file_compression`

  >   Changed in version 1.2: Added Google Snappy compression algorithm.

  >   Method used to compress everything that is appended to database and view index files, except for attachments (see the `attachments` section). Available methods are:

  >   - `none`: no compression
  >   - `snappy`: use Google Snappy, a very fast compressor/decompressor
  >   - `deflate_N`: use zlib’s deflate; `N` is the compression level which ranges from `1` (fastest, lowest compression ratio) to `9` (slowest, highest compression ratio)

  >       [couchdb]
  >       file_compression = snappy

  > `fsync_options`

  >   Specifies when to make fsync calls. fsync makes sure that the contents of any file system buffers kept by the operating system are flushed to disk. There is generally no need to modify this parameter.

  >       [couchdb]
  >       fsync_options = [before_header, after_header, on_file_open]

  > `max_dbs_open`

  >   This option places an upper bound on the number of databases that can be open at once. CouchDB reference counts database accesses internally and will close idle databases as needed. Sometimes it is necessary to keep more than the default open at once, such as in deployments where many databases will be replicating continuously.

  >       [couchdb]
  >       max_dbs_open = 100

  > `os_process_timeout`

  >   If an external process, such as a query server or external process, runs for this amount of milliseconds without returning any results, it will be terminated. Keeping this value smaller ensures you get expedient errors, but you may want to tweak it for your specific needs.

  >       [couchdb]
  >       os_process_timeout = 5000 ; 5 sec

  > `uri_file`

  >   This file contains the full URI that can be used to access this instance of CouchDB. It is used to help discover the port CouchDB is running on (if it was set to `0` (e.g. automatically assigned any free one). This file should be writable and readable for the user that runs the CouchDB service (`couchdb` by default).

  >       [couchdb]
  >       uri_file = /var/run/couchdb/couchdb.uri

  `users_db_suffix`

    > Specifies the suffix (last component of a name) of the system database for storing CouchDB users.

    >     [couchdb]
    >     users_db_suffix = _users

    > Warning

    > If you change the database name, do not forget to remove or clean up the old database, since it will no longer be protected by CouchDB.

    `util_driver_dir`

      Specifies location of binary drivers (icu, ejson, etc.). This location and its contents should be readable for the user that runs the CouchDB service.

          [couchdb]
          util_driver_dir = /usr/lib/couchdb/erlang/lib/couch-1.5.0/priv/lib

    `uuid`

      New in version 1.3.

      Unique identifier for this CouchDB server instance.

          [couchdb]
          uuid = 0a959b9b8227188afc2ac26ccdf345a6

    `view_index_dir`

      Specifies location of CouchDB view index files. This location should be writable and readable for the user that runs the CouchDB service (`couchdb` by default).

          [couchdb]
          view_index_dir = /var/lib/couchdb

    `maintenance_mode`

      A CouchDB node may be put into two distinct maintenance modes by setting this configuration parameter.

      - `true`: The node will not respond to clustered requests from other nodes and the /_up endpoint will return a 404 response.
      - `nolb`: The /_up endpoint will return a 404 response.
      - `false`: The node responds normally, /_up returns a 200 response.

      It is expected that the administrator has configured a load balancer in front of the CouchDB nodes in the cluster. This load balancer should use the /_up endpoint to determine whether or not to send HTTP requests to any particular node. For HAProxy, the following config is appropriate:

          http-check disable-on-404
          option httpchk GET /_up

    `max_document_size`

      Changed in version 2.1.0.

      Limit maximum document body size. Size is calculated based on the serialized Erlang representation of the JSON document body, because that reflects more accurately the amount of storage consumed on disk.

      HTTP requests which create or update documents will fail with error code 413 if one or more documents is larger than this configuration value.

      In case of _update handlers, document size is checked after the transformation and right before being inserted into the database.

          [couchdb]
          max_document_size = 4294967296 ; 4 GB

      Warning

      Before version 2.1.0 this setting was implemented by simply checking http request body sizes. For individual document updates via PUT that approximation was close enough, however that is not the case for _bulk_docs endpoint. After 2.1.0 a separate configuration parameter was defined: `httpd/max_http_request_size`, which can be used to limit maximum http request sizes. After upgrade, it is advisable to review those settings and adjust them accordingly.