Data Formats

ACHE can store data in different data formats. The data format can be configured by changing the key target_storage.data_format.type in the configuration file.

The data formats currently available are:


Each page is stored in a single file, and files are organized in directories (one for each domain). The suffix in the data format name determines how content of each file is formatted:

  • FILESYSTEM_HTML - only raw content (HTML, or binary data) is stored in files. Useful for testing and opening the files HTML using the browser.
  • FILESYSTEM_JSON - raw content and some metadata is stored using JSON format in files.
  • FILESYSTEM_CBOR - raw content and some metadata is stored using CBOR format in files.

When using any FILESYSTEM_* data format, you can enable compression (DEFLATE) of the data stored in the files enabling the following line in the config file:

target_storage.data_format.filesystem.compress_data: true

By default, the name of each file will be an encoded URL. Unfortunately, this can cause problems in some cases where the URL is very long. To fix this you can configure the file format to use a fixed size hash of the URL, instead of URL itself as a file name:

target_storage.data_format.filesystem.hash_file_name: true


All FILESYSTEM_* formats are not recommended for large crawls, since they can create millions files quickly and cause file system problems.


Raw content and metadata are stored in rolling compressed files of fixed size (256MB). Each file is a JSON lines file (each line contains one JSON object) compressed using the DEFLATE algorithm. Each JSON object has the following fields:

  • url - The requested URL
  • redirected_url - The URL of final redirection if it applies
  • content - A Base64 encoded string containing the page content
  • content_type - The mime-type returned in the HTTP response
  • response_headers - An array containing the HTTP response headers
  • fetch_time - A integer containing the time when the page was fetched (epoch)


Raw content and metadata are stored in WARC files. WARC is the standard format used by The Web Archive and other public web datasets such as “Common Crawl” and “ClueWeb”. See for more details on the WARC format.

Every WARC file generated by ACHE contains one warcinfo entry and one response entry for each downloaded page. By default, the files are compressed using GZIP format and have an approximate size of 250MB (usually slightly larger). The default settings can be changed using the following entries in ache.yml file:

target_storage.data_format.type: WARC                    # enable WARC file format
target_storage.data_format.warc.compress: true           # enable GZIP compression
target_storage.data_format.warc.max_file_size: 262144000 # maximum file size in bytes

Finally, ACHE also stores additional metadata as non-standard extension WARC headers prefixed by ACHE-* (e.g., ACHE-IsRelevant, ACHE-Relevance).


The ELASTICSEARCH data format stores raw content and metadata as documents in an Elasticsearch index.

Types and fields

Currently, ACHE indexes documents into one Elasticsearch type named page (or any name specified using the command line during the crawl initialization). The Elasticsearch mapping for this type is automatically created and contains the following fields:

  • domain - domain of the URL
  • topPrivateDomain - top private domain of the URL
  • url - complete URL
  • title - title of the page extracted from the HTML tag <title>
  • text - clean text extract from HTML using Boilerpipe’s DefaultExtractor
  • retrieved - date when the time was fetched using ISO-8601 representation Ex: “2015-04-16T07:03:50.257+0000”
  • words - array of strings with tokens extracted from the text content
  • wordsMeta - array of strings with tokens extracted from tags <meta> of the HTML content
  • html - raw HTML content
  • isRelevant - indicates whether the page was classified as relevant or irrelevant by target page classifier. This is a keyword field (not analyzed string) containing either relevant or irrelevant.
  • relevance - indicates the confidence of the target page classifier output. This is a decimal number with range from 0.0 to 1.0.


To use Elasticsearch data format, you need to add the following line to the configuration file ache.yml:

target_storage.data_format.type: ELASTICSEARCH

You will also need to specify the host address and port where Elasticsearch is running. See the following subsections for more details.

REST Client (ACHE version >0.8)

Starting in version 0.8, ACHE uses the official Java REST client to connect to Elasticsearch. You can specify one or more Elasticsearch node addresses which the REST client should connect to using the following lines:
  - http://node1:9200
  - http://node2:9200

The following additional parameters can also be configured. Refer to the Elasticsearch REST Client documentation for more information on these parameters. 30000 30000 90000

Transport Client (deprecated)

You can also configure ACHE to connect to Elasticsearch v1.x using the native transport client by adding the following lines: localhost
target_storage.data_format.elasticsearch.port: 9300
target_storage.data_format.elasticsearch.cluster_name: elasticsearch

Command line parameters

When running ACHE using Elasticsearch, you must provide the name of the Elasticsearch index that will be used as an argument to the CLI using the following parameters:

-e <arg>


--elasticIndex <arg>

You can also (optional) provide the Elasticsearch type name to be used:

-t <arg>


--elasticType <arg>

Run ache help startCrawl for more details on available parameters.


The KAFKA data format pushes crawled pages to an Apache Kafka topic. To configure this format, add the following lines to the ache.yml configuration file:

target_storage.data_format.type: KAFKA                    # enable KAFKA file format
target_storage.data_format.kafka.topic_name: mytopicname  # the name of the topic
target_storage.data_format.kafka.format: JSON             # value of messages will be a JSON object
  # The properties to be used while initializing the Kafka Producer
  bootstrap.servers: localhost:9092
  acks: all
  retries: 0
  batch.size: 5 100
  buffer.memory: 33554432

Currently, following message formats are supported:

  • JSON: A JSON object using same schema defined in the FILES data format.
  • CDR31: A JSON object formatted using the Memex CDR v3.1 format. Image objects are currently not supported.