Slow Log

Shard level slow search log allows to log slow search (query and fetch phases) into a dedicated log file.

Thresholds can be set for both the query phase of the execution, and fetch phase, here is a sample:

index.search.slowlog.threshold.query.warn: 10s
index.search.slowlog.threshold.query.info: 5s
index.search.slowlog.threshold.query.debug: 2s
index.search.slowlog.threshold.query.trace: 500ms

index.search.slowlog.threshold.fetch.warn: 1s
index.search.slowlog.threshold.fetch.info: 800ms
index.search.slowlog.threshold.fetch.debug: 500ms
index.search.slowlog.threshold.fetch.trace: 200ms

All of the above settings are dynamic and can be set per-index.

By default, none are enabled (set to -1). Levels (warn, info, debug, trace) allow to control under which logging level the log will be logged. Not all are required to be configured (for example, only warn threshold can be set). The benefit of several levels is the ability to quickly "grep" for specific thresholds breached.

The logging is done on the shard level scope, meaning the execution of a search request within a specific shard. It does not encompass the whole search request, which can be broadcast to several shards in order to execute. Some of the benefits of shard level logging is the association of the actual execution on the specific machine, compared with request level.

The logging file is configured by default using the following configuration (found in logging.yml):

index_search_slow_log_file:
  type: dailyRollingFile
  file: ${path.logs}/${cluster.name}_index_search_slowlog.log
  datePattern: "'.'yyyy-MM-dd"
  layout:
    type: pattern
    conversionPattern: "[%d{ISO8601}][%-5p][%-25c] %m%n"

The indexing slow log, similar in functionality to the search slow log. The log file name ends with _index_indexing_slowlog.log. Log and the thresholds are configured in the elasticsearch.yml file in the same way as the search slowlog. Index slowlog sample:

index.indexing.slowlog.threshold.index.warn: 10s
index.indexing.slowlog.threshold.index.info: 5s
index.indexing.slowlog.threshold.index.debug: 2s
index.indexing.slowlog.threshold.index.trace: 500ms
index.indexing.slowlog.level: info
index.indexing.slowlog.source: 1000

All of the above settings are dynamic and can be set per-index.

By default Elasticsearch will log the first 1000 characters of the _source in the slowlog. You can change that with index.indexing.slowlog.source. Setting it to false or 0 will skip logging the source entirely an setting it to true will log the entire source regardless of size.

The index slow log file is configured by default in the logging.yml file:

index_indexing_slow_log_file:
    type: dailyRollingFile
    file: ${path.logs}/${cluster.name}_index_indexing_slowlog.log
    datePattern: "'.'yyyy-MM-dd"
    layout:
      type: pattern
      conversionPattern: "[%d{ISO8601}][%-5p][%-25c] %m%n"