Introducing Couchbase Sync Gateway’s logging functionality
      Sync Gateway’s _Continuous Logging_ feature delivers flexible log generation and retention, without compromising the availability of diagnostic information necessary to provide effective support and maintenance.


      Do not use the logs directory as a storage location for files that should not be there. Permission issues with those files can prevent Sync Gateway from starting.


      Sync Gateway provides a robust Continuous Logging[1] solution that delivers flexibility in terms of how logs are generated and retained, whilst also maintaining the level of logging required by Couchbase Support for investigation of issues. Its logs are written to separate log files filtered by log level, with each log level supporting individual retention policies. You control what is logged using the Bootstrap Configuration logging properties [fnleg3-0].

      In addition to the log files, you can also independently configure and control Console Logging, which is a convenient method of accessing diagnostic information during debugging scenarios. With console logging, system administrators can easily fine-tune diagnostic output to suit specific debug scenarios. All without interfering with the logging required by Couchbase Support for the investigation of issues.


      You configure continuous and console logging requirements in the Bootstrap Configuration file, using the logging properties [2]  — see: Example 1.

      Example 1. Sample Logging Configuration
        "logging": {
          "log_file_path": "/var/tmp/sglogs", (1)
          "redaction_level": "partial", (2)
          "console": { (3)
            "log_level": "debug",
            "log_keys": ["*"]
            }, (4)
          "error": { (5)
            "enabled": true,
            "rotation": {
              "max_size": 20,
              "max_age": 180
          "warn": { (6)
            "enabled": true,
            "rotation": {
              "max_size": 20,
              "max_age": 90
          "info": { (7)
            "enabled": false
          "debug": { (8)
            "enabled": false
      1 Set the path to the log file(s)
      2 Define the optional redaction level, here we select "partial" redaction — see: Log Redaction
      3 Here we define the Console Logging levels we require for debugging. In this instance turning on debug level output for all available log_keys — see: logging.console.log_keys [2]
      4 The following logging properties enable, or disable, Continuous Logging at the specified level — see: logging.console.log_level [2]
      5 Here we set error level logging on and define the log-file rotation, for errors messages
      6 Here we set warn level logging on and define the log-file rotation, for warnings messages
      7 Here we set info level logging off; we do not define the log-file rotation
      8 Here we set debug level logging off; we do not define the log-file rotation

      See: Bootstrap Configuration for more information on these settings [2].

      Log Redaction

      All log outputs — console or continuous — can optionally be redacted, which will remove any user-data considered private.

      You enable this feature by setting the logging.redaction_level property [2].

      Console Logging

      By default only HTTP logging is enabled

      Console logs are your go-to resource for diagnostic information. You can easily fine-tune their diagnostic content to meet the needs of a particular debugging scenario, perhaps by increasing the verbosity and filtering out unnecessary log_keys to better focus on the problem area.

      Changes to console logging are independent of continuous logging, so you can, for example, tweak any of the following without compromising the core continuous logging streams:

      • Increase the verbosity using Log Levels to generate additional diagnostic information

      • Focus on the area under investigation by enabling or disabling specific Log Keys

      • Enhance readability by setting a color for log output based on log level

      Admin REST API

      You can define console log settings in the bootstrap configuration file, or more conveniently, you can use the Admin REST API’s _config endpoint to set them — see: Example 2.

      Example 2. Setting log_level and log_keys with API
      curl --location --request PUT 'http://localhost:4985/_config' \
      --header 'Content-Type: application/json' \
      --data-raw '{
          "console": {
              "log_level": "trace", (1)
              "log_keys": "[\"WS\",\"WSFrame\",\"Replicate\"]",  (2)
      1 Here we define the log_level to be trace for maximum verbosity
      2 Here we specify the particular log_keys we want to focus on.
      Note here we have chosen to exclude http; perhaps we want to focus on a websocket or replication issue.

      The console log will show the following after this command:

      2021-01-08T13:26:23.884Z [INF] HTTP:  #110: POST /_logging?logLevel=trace (as ADMIN)
      2021-01-08T13:26:23.885Z [INF] Setting log level to: trace
      2021-01-08T13:26:23.885Z [INF] Setting log keys to: [DCP Replicate WS WSFrame]

      Log Levels

      When debugging, setting the console log’s log-level to debug or trace can provide valuable additional information

      Console logs have six levels of verbosity — see: Table 1. The default log level is none

      Note that the log levels are inclusive, so if you enable info level, then warn and error logs are also enabled.

      You can define console log levels in the configuration file — see logging.console.log_level [2] and by using the Admin REST API (see: Example 2).

      One approach might be to set your base level in the configuration file and then use the Admin REST API for specific debugging scenarios.

      Table 1. Console Logging — Available Log Levels

      Log Level





      Disables log output



      Displays errors that need urgent attention



      Displays warnings that need some attention



      Displays information about normal operations that don’t need attention



      Displays verbose output that might be useful when debugging



      Displays extremely verbose output that might be useful when debugging

      Log Keys

      Select log keys relevant to the area you are debugging, providing them as a comma-delimited list, such as: "log_keys": ["HTTP", "CRUD", "Import"] in the config or see Example 2 for how to provide them using the Admin REST API.

      Log keys provide fine-grained control over the information types that Sync Gateway outputs to the console log. By default, only HTTP related information is enabled, but a range of other keys are available to meet specific diagnostic needs — see: Table 2.

      You can define the required logging.console.log_keys within your configuration file and-or use the Admin REST API (see: Example 2).

      Table 2. List of Available Log Keys

      Log Key



      This wildcard log key, enables all log keys

      curl --location --request PUT 'http://localhost:4985/_config' \
      --header 'Content-Type: application/json' \
      --data-raw '{
          "console": {
            "log_keys": "[\"*\"]


      Disable all log keys; no logging output

      curl --location --request PUT 'http://localhost:4985/_config' \
      --header 'Content-Type: application/json' \
      --data-raw '{
          "console": {
              "log_keys": "[\"none\"]


      Admin processes in Sync Gateway.


      Anytime an access() call is made in the sync function.




      Sync Gateway interactions with the bucket.


      Interactions with Sync Gateway’s in-memory channel cache.


      Processing of /{db}/_changes requests.


      Updates made by Sync Gateway to documents.


      DCP-feed processing.


      Event processing (webhooks).


      All logging emitted by the GoCB SDK


      All requests made to the Sync Gateway REST APIs.


      Additional information about HTTP requests (response times, status codes).


      This log key can be useful to troubleshoot why a given document was not successfully imported.


      All logging from Javascript. This includes: sync function, import filters, webhook filter function, and custom inter-Sync Gateway replication conflict resolvers


      Logs messages that show when old inline document metadata is upgraded to xattrs


      Query is used for Sync Gateway code related to N1QL queries


      Log messages related to replications between Sync Gateways (using sg-replicate). This tag cannot be used for replications initiated by Couchbase Lite.


      Log messages related to the sharded import and HA sg-replicate


      Activity which relates to synchronization between Couchbase Lite and Sync Gateway


      Can be used for additional Sync logging output


      Websocket replication log messages


      Can be used for additional WS logging output

      Set Log Color

      To use color for log output based on log level, set logging.console.color_enabled to true

      This setting is always disabled on Windows for compatibility reasons.

      Redirect Console Log

      You can easily redirect the console log output to a file. This can be useful not only for diagnostic sessions, but also when you have specialized logging requirements, such as centralized logging. Just redirect the output and then apply your own log collection mechanism to feed that data elsewhere — see Example 3.

      Example 3. Console Log Redirection
      # Start Sync Gateway and redirect console output to a file
      ./sync-gateway > my_sg_logs.txt 2>&1
      # Start log collection to send to a centralized log aggregator.
      logcollector my_sg_logs.txt

      Continuous Logging

      In this section: Log File Outputs | Log File Rotation

      Continuous logging produces a set of log files aimed primarily at providing appropriate diagnostic information for the Couchbase Support team should their intervention be required. You define continuous logging settings in the configuration file — see: Example 1.

      With continuous logging the logs for each level are written to separate log files — see: Table 3. You can set individual retention policies for each log-level.

      Log File Outputs

      The log files output from continuous logging are intended solely for the use of Couchbase Support.

      If you require special log handling, for example for centralized logging, then use the Redirect Console Log feature to create a log file for this purpose from the console output stream.

      Sync Gateway produces four separate log files, split by log level. Each log file has its own guaranteed retention period - as shown in Table 3

      You can collect the log files, for analysis by Couchbase Support when diagnosing Sync Gateway issues, using SGCollect Info.

      Table 3. Continuos Logging - Log File Outputs

      Log File



      Default enabled

      Default max_age

      Minimum max_age


      Critical error messages.



      360 Days

      180 Days


      Something is wrong but SG can still service requests



      180 Days

      90 Days


      Important diagnostics for support and customers



      6 Days

      3 Days


      Lower level development analysis



      2 Days

      1 Day

      Each log level and its parameters are defined using the logging.console.log_level property.

      Log File Rotation

      Log files are rotated when they exceed a threshold max_size (megabytes). Once rotated, they are compressed (gzip) to reduce the disk usage.

      Aged logs are cleaned up once their age exceeds max_age days — see: Table 3

      Configure log rotation using the logging.console.rotation property.

      For pre-2.1 log rotation — see: Pre 2.1 Log Rotation