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# 3.12. Miscellaneous Parameters

## 3.12.1. Configuration of Attachment Storage

`[attachments]`
  `compression_level`

    Defines zlib compression level for the attachments from `1` (lowest, fastest) to `9` (highest, slowest). A value of `0` disables compression

        [attachments]
        compression_level = 8

  `compressible_types`

    Since compression is ineffective for some types of files, it is possible to let CouchDB compress only some types of attachments, specified by their MIME type:

        [attachments]
        compressible_types = text/*, application/javascript, application/json, application/xml

## 3.12.2. Statistic Calculation

`[stats]`
  `rate`

    Rate of statistics gathering in milliseconds:

        [stats]
        rate = 1000

  `samples`

    Samples are used to track the mean and standard value deviation within specified intervals (in seconds):

        [stats]
        samples = [0, 60, 300, 900]

## 3.12.3. UUIDs Configuration

`[uuids]`
  `algorithm`

    Changed in version 1.3: Added `utc_id` algorithm.

    CouchDB provides various algorithms to generate the UUID values that are used for document _id‘s by default:

        [uuids]
        algorithm = sequential

    Available algorithms:

    - `random`: 128 bits of random awesome. All awesome, all the time:

          {
            "uuids": [
              "5fcbbf2cb171b1d5c3bc6df3d4affb32",
              "9115e0942372a87a977f1caf30b2ac29",
              "3840b51b0b81b46cab99384d5cd106e3",
              "b848dbdeb422164babf2705ac18173e1",
              "b7a8566af7e0fc02404bb676b47c3bf7",
              "a006879afdcae324d70e925c420c860d",
              "5f7716ee487cc4083545d4ca02cd45d4",
              "35fdd1c8346c22ccc43cc45cd632e6d6",
              "97bbdb4a1c7166682dc026e1ac97a64c",
              "eb242b506a6ae330bda6969bb2677079"
            ]
          }

    - `sequential`: Monotonically increasing ids with random increments. The first 26 hex characters are random, the last 6 increment in random amounts until an overflow occurs. On overflow, the random prefix is regenerated and the process starts over.

          {
            "uuids": [
              "4e17c12963f4bee0e6ec90da54804894",
              "4e17c12963f4bee0e6ec90da5480512f",
              "4e17c12963f4bee0e6ec90da54805c25",
              "4e17c12963f4bee0e6ec90da54806ba1",
              "4e17c12963f4bee0e6ec90da548072b3",
              "4e17c12963f4bee0e6ec90da54807609",
              "4e17c12963f4bee0e6ec90da54807718",
              "4e17c12963f4bee0e6ec90da54807754",
              "4e17c12963f4bee0e6ec90da54807e5d",
              "4e17c12963f4bee0e6ec90da54808d28"
            ]
          }

    - `utc_random`: The time since Jan 1, 1970 UTC, in microseconds. The first 14 characters are the time in hex. The last 18 are random.

          {
            "uuids": [
              "04dd32b3af699659b6db9486a9c58c62",
              "04dd32b3af69bb1c2ac7ebfee0a50d88",
              "04dd32b3af69d8591b99a8e86a76e0fb",
              "04dd32b3af69f4a18a76efd89867f4f4",
              "04dd32b3af6a1f7925001274bbfde952",
              "04dd32b3af6a3fe8ea9b120ed906a57f",
              "04dd32b3af6a5b5c518809d3d4b76654",
              "04dd32b3af6a78f6ab32f1e928593c73",
              "04dd32b3af6a99916c665d6bbf857475",
              "04dd32b3af6ab558dd3f2c0afacb7d66"
            ]
          }

    - `utc_id`: The time since Jan 1, 1970 UTC, in microseconds, plus the `utc_id_suffix` string. The first 14 characters are the time in hex. The `uuids/utc_id_suffix` string value is appended to these.

          {
            "uuids": [
              "04dd32bd5eabcc@mycouch",
              "04dd32bd5eabee@mycouch",
              "04dd32bd5eac05@mycouch",
              "04dd32bd5eac28@mycouch",
              "04dd32bd5eac43@mycouch",
              "04dd32bd5eac58@mycouch",
              "04dd32bd5eac6e@mycouch",
              "04dd32bd5eac84@mycouch",
              "04dd32bd5eac98@mycouch",
              "04dd32bd5eacad@mycouch"
            ]
          }

    Note

    Impact of UUID choices: the choice of UUID has a significant impact on the layout of the B-tree, prior to compaction.

    For example, using a sequential UUID algorithm while uploading a large batch of documents will avoid the need to rewrite many intermediate B-tree nodes. A random UUID algorithm may require rewriting intermediate nodes on a regular basis, resulting in significantly decreased throughput and wasted disk space space due to the append-only B-tree design.

    It is generally recommended to set your own UUIDs, or use the sequential algorithm unless you have a specific need and take into account the likely need for compaction to re-balance the B-tree and reclaim wasted space.

  `utc_id_suffix`

    New in version 1.3.

    The `utc_id_suffix` value will be appended to UUIDs generated by the `utc_id` algorithm. Replicating instances should have unique `utc_id_suffix` values to ensure uniqueness of `utc_id` ids.

        [uuid]
        utc_id_suffix = my-awesome-suffix

  `max_count`

    New in version 1.5.1.

    No more than this number of UUIDs will be sent in a single request. If more UUIDs are requested, an HTTP error response will be thrown.

        [uuid]
        max_count = 1000

## 3.12.4. Vendor information

`[vendor]`

  New in version 1.3.

  CouchDB distributors have the option of customizing CouchDB’s welcome message. This is returned when requesting `GET /`.

      [vendor]
      name = The Apache Software Foundation
      version = 1.5.0

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