.. Licensed under the Apache License, Version 2.0 (the "License"); you may not .. use this file except in compliance with the License. You may obtain a copy of .. the License at .. .. http://www.apache.org/licenses/LICENSE-2.0 .. .. Unless required by applicable law or agreed to in writing, software .. distributed under the License is distributed on an "AS IS" BASIS, WITHOUT .. WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the .. License for the specific language governing permissions and limitations under .. the License. .. highlight:: ini ============= Query Servers ============= .. _config/query_servers: Query Servers Definition ======================== .. versionchanged:: 2.3 Changed configuration method for Query Servers and Native Query Servers. CouchDB delegates computation of :ref:`design documents ` functions to external query servers. The external query server is a special OS process which communicates with CouchDB over standard input/output using a very simple line-based protocol with JSON messages. An external query server may be defined with environment variables following this pattern:: COUCHDB_QUERY_SERVER_LANGUAGE="PATH ARGS" Where: - ``LANGUAGE``: is a programming language which code this query server may execute. For instance, there are `PYTHON`, `RUBY`, `CLOJURE` and other query servers in the wild. This value in *lowercase* is also used for ``ddoc`` field ``language`` to determine which query server processes the functions. Note, that you may set up multiple query servers for the same programming language, but you have to name them differently (like `PYTHONDEV` etc.). - ``PATH``: is a system path to the executable binary program that runs the query server. - ``ARGS``: optionally, you may specify additional command line arguments for the executable ``PATH``. The default query server is written in :ref:`JavaScript `, running via `Mozilla SpiderMonkey`_. It requires no special environment settings to enable, but is the equivalent of these two variables:: COUCHDB_QUERY_SERVER_JAVASCRIPT="/opt/couchdb/bin/couchjs /opt/couchdb/share/server/main.js" COUCHDB_QUERY_SERVER_COFFEESCRIPT="/opt/couchdb/bin/couchjs /opt/couchdb/share/server/main-coffee.js" By default, ``couchjs`` limits the max runtime allocation to 64MiB. If you run into out of memory issue in your ddoc functions, you can adjust the memory limitation (here, increasing to 512 MiB):: COUCHDB_QUERY_SERVER_JAVASCRIPT="/usr/bin/couchjs -S 536870912 /usr/share/server/main.js" For more info about the available options, please consult ``couchjs -h``. .. note:: CouchDB versions 3.0.0 to 3.2.2 included a performance regression for custom reduce functions. CouchDB 3.3.0 and later come with an experimental fix to this issue that is included in a separate ``.js`` file. To enable the fix, you need to define a custom ``COUCHDB_QUERY_SERVER_JAVASCRIPT`` environment variable as outlined above. The path to ``couchjs`` needs to remain the same as you find it on your ``couchdb`` file, and the path to ``main.js`` needs to be set to ``/path/to/couchdb/share/server/main-ast-bypass.js``. With a default installation on Linux systems, this is going to be ``COUCHDB_QUERY_SERVER_JAVASCRIPT="/opt/couchdb/bin/couchjs /opt/couchdb/share/server/main-ast-bypass.js"`` .. _Mozilla SpiderMonkey: https://spidermonkey.dev/ .. seealso:: The :ref:`Mango Query Server ` is a declarative language that requires *no programming*, allowing for easier indexing and finding of data in documents. The :ref:`Native Erlang Query Server ` allows running `ddocs` written in Erlang natively, bypassing stdio communication and JSON serialization/deserialization round trip overhead. .. _config/query_server_config: Query Servers Configuration =========================== .. config:section:: query_server_config :: Query Servers Configuration .. config:option:: commit_freq :: View index commit delay Specifies the delay in seconds before view index changes are committed to disk. The default value is ``5``:: [query_server_config] commit_freq = 5 .. config:option:: os_process_limit :: Query Server process hard limit Hard limit on the number of OS processes usable by Query Servers. The default value is ``100``:: [query_server_config] os_process_limit = 100 Setting ``os_process_limit`` too low can result in starvation of Query Servers, and manifest in ``os_process_timeout`` errors, while setting it too high can potentially use too many system resources. Production settings are typically 10-20 times the default value. .. config:option:: os_process_soft_limit :: Query Server process soft limit Soft limit on the number of OS processes usable by Query Servers. The default value is ``100``:: [query_server_config] os_process_soft_limit = 100 Idle OS processes are closed until the total reaches the soft limit. For example, if the hard limit is 200 and the soft limit is 100, the total number of OS processes will never exceed 200, and CouchDB will close all idle OS processes until it reaches 100, at which point it will leave the rest intact, even if some are idle. .. config:option:: reduce_limit :: Reduce limit control Controls `Reduce overflow` error that raises when output of :ref:`reduce functions ` is too big:: [query_server_config] reduce_limit = true Normally, you don't have to disable (by setting ``false`` value) this option since main propose of `reduce` functions is to *reduce* the input. .. _config/native_query_servers: Native Erlang Query Server ========================== .. config:section:: native_query_servers :: Native Erlang Query Server .. warning:: Due to security restrictions, the Erlang query server is disabled by default. Unlike the JavaScript query server, the Erlang one does not run in a sandbox mode. This means that Erlang code has full access to your OS, file system and network, which may lead to security issues. While Erlang functions are faster than JavaScript ones, you need to be careful about running them, especially if they were written by someone else. CouchDB has a native Erlang query server, allowing you to write your map/reduce functions in Erlang. First, you'll need to edit your `local.ini` to include a ``[native_query_servers]`` section:: [native_query_servers] enable_erlang_query_server = true To see these changes you will also need to restart the server. Let's try an example of map/reduce functions which count the total documents at each number of revisions (there are x many documents at version "1", and y documents at "2"... etc). Add a few documents to the database, then enter the following functions as a view: .. code-block:: erlang %% Map Function fun({Doc}) -> <> = proplists:get_value(<<"_rev">>, Doc, null), V = proplists:get_value(<<"_id">>, Doc, null), Emit(<>, V) end. %% Reduce Function fun(Keys, Values, ReReduce) -> length(Values) end. If all has gone well, after running the view you should see a list of the total number of documents at each revision number. Additional examples are on the `users@couchdb.apache.org mailing list `_. .. _config/search: Search ====== CouchDB's search subsystem can be configured via the ``dreyfus`` configuration section. .. config:section:: dreyfus :: Search Subsystem Configuration .. config:option:: name :: Clouseau JVM node name and location The name and location of the Clouseau Java service required to enable Search functionality. Defaults to ``clouseau@127.0.0.1``. .. config:option:: retry_limit :: Maximum number of connection retries CouchDB will try to reconnect to Clouseau using a bounded exponential backoff with the following number of iterations. Defaults to ``5``. .. config:option:: limit :: Default result set limit for global search The number of results returned from a global search query if no limit is specified. Defaults to ``25``. .. config:option:: limit_partitions :: Default result set limit for partitioned DBs The number of results returned from a search on a partition of a database if no limit is specified. Defaults to ``2000``. .. config:option:: max_limit :: Maximum result set for global search The maximum number of results that can be returned from a global search query (or any search query on a database without user-defined partitions). Attempts to set ``?limit=N higher`` than this value will be rejected. Defaults to ``200``. .. config:option:: max_limit_partitions :: Maximum result set for partitioned search The maximum number of results that can be returned when searching a partition of a database. Attempts to set ``?limit=N`` higher than this value will be rejected. If this config setting is not defined, CouchDB will use the value of ``max_limit`` instead. If neither is defined, the default is ``2000``. Nouveau ======= CouchDB's experimental search subsystem can be configured via the ``nouveau`` configuration section. .. config:section:: nouveau :: Nouveau Server Configuration .. config:option:: enable :: Whether nouveau is enabled Set to ``true`` to enable Nouveau. If disabled, all nouveau endpoints return 404 Not Found. Defaults to ``false``. .. config:option:: url :: Nouveau Server location The URL to a running nouveau server. Defaults to ``http://127.0.0.1:8080``. .. config:option:: max_sessions :: Maximum number of ibrowse sessions Nouveau will configure ibrowse max_sessions to this value for the configured ``url``. Defaults to ``100``. .. config:option:: max_pipeline_size :: Max pipeline size Nouveau will configure ibrowse max_pipeline_size to this value for the configured ``url``. Defaults to ``1000``. .. _config/mango: Mango ===== Mango is the Query Engine that services the :ref:`_find `, endpoint. .. config:section:: mango :: Mango Configuration .. config:option:: index_all_disabled :: Disable "index all fields" behaviour Set to ``true`` to disable the "index all fields" text index. This can lead to out of memory issues when there are documents with nested array fields. Defaults to ``false``. :: [mango] index_all_disabled = false .. config:option:: default_limit :: Default limit value for Mango queries. Sets the default number of results that will be returned in a :ref:`_find ` response. Individual requests can override this by setting ``limit`` directly in the query parameters. Defaults to ``25``. :: [mango] default_limit = 25 .. config:option:: index_scan_warning_threshold :: Ratio threshold that generates \ an index scan warning This sets the ratio between documents scanned and results matched that will generate a warning in the _find response. For example, if a query requires reading 100 documents to return 10 rows, a warning will be generated if this value is ``10``. Defaults to ``10``. Setting the value to ``0`` disables the warning. :: [mango] index_scan_warning_threshold = 10