Gerrit supports on-demand tracing of single requests that results in additional logs with debug information that are written to the error_log. The logs that correspond to a traced request are associated with a unique trace ID. This trace ID is returned with the response and can be used by an administrator to find the matching log entries.

How tracing is enabled and how the trace ID is returned depends on the request type:

  • REST API: For REST calls tracing can be enabled by setting the trace request parameter or the X-Gerrit-Trace header, the trace ID is returned as X-Gerrit-Trace header. More information about this can be found in the Request Tracing section of the REST API documentation.

  • SSH API: For SSH calls tracing can be enabled by setting the --trace option. More information about this can be found in the Trace section of the SSH command documentation.

  • Git: For Git pushes tracing can be enabled by setting the trace push option, the trace ID is returned in the command output. More information about this can be found in the Trace section of the upload documentation. Tracing for Git requests other than Git push is not supported.

When request tracing is enabled it is possible to provide an ID that should be used as trace ID. If a trace ID is not provided a trace ID is automatically generated. The trace ID must be provided to the support team so that they can find the trace.

When doing traces it is recommended to specify the ID of the issue that is being investigated as trace ID so that the traces of the issue can be found more easily. When the issue ID is used as trace ID there is no need to find the generated trace ID and report it in the issue.

Since tracing consumes additional server resources tracing should only be enabled for single requests if there is a concrete need for debugging. In particular bots should never enable tracing for all their requests by default.

Find log entries for a trace ID

If tracing is enabled all log messages that correspond to the traced request have a TRACE_ID tag set, e.g.:

[2018-08-13 15:28:08,913] [HTTP-76] TRACE com.google.gerrit.httpd.restapi.RestApiServlet : Received REST request: GET /a/accounts/self (parameters: [trace]) [CONTEXT forced=true TRACE_ID="1534166888910-3985dfba" ]
[2018-08-13 15:28:08,914] [HTTP-76] TRACE com.google.gerrit.httpd.restapi.RestApiServlet : Calling user: admin [CONTEXT forced=true TRACE_ID="1534166888910-3985dfba" ]
[2018-08-13 15:28:08,942] [HTTP-76] TRACE com.google.gerrit.httpd.restapi.RestApiServlet : REST call succeeded: 200 [CONTEXT forced=true TRACE_ID="1534166888910-3985dfba" ]

By doing a grep with the trace ID over the error log the log entries that correspond to the request can be found.

Which information is captured in a trace?

  • request details

    • REST API: request URL, request parameter names, calling user, response code, response body on errors

    • SSH API: parameter names

    • Git API: push options, magic branch parameter names

  • cache misses, cache evictions

  • reads from NoteDb, writes to NoteDb

  • reads of meta data files, writes of meta data files

  • index queries (with parameters and matches)

  • reindex events

  • permission checks (e.g. which rule is responsible for a deny)

  • timer metrics

  • all other logs