MarkLogic 10 Product Documentation

Application Developer's Guide — Chapter 4

Setting the Large Size Threshold

The large size threshold database setting defines the maximum size of a small binary, in kilobytes. Any binary documents larger than this threshold are large and are stored in the Large Data Directory, as described in Choosing a Binary Format. The threshold has no effect on external binaries.

For example, a threshold of 1024 sets the size threshold to 1 MB. Any (managed) binary document larger than 1 MB is automatically handled as a large binary object.

The range of acceptable threshold values on a 64-bit machine is 32 KB to 512 MB, inclusive.

Many factors must be considered in choosing the large size threshold, including the data characteristics, the access patterns of the application, and the underlying hardware and operating system. Ideally, set the threshold such that smaller, frequently accessed binary content such as thumbnails and profile images are classified as small for efficient access, while larger documents such as movies and music, which may be streamed by the application, are classified as large for efficient memory usage.

The threshold may be set through the Admin Interface or by calling an admin API function. To set the threshold through the Admin Interface, use the large size threshold setting on the database configuration page.To set the threshold programmatically, use the XQuery built-in admin:database-set-large-size-threshold:

xquery version "1.0-ml"; 

import module namespace admin = "http://marklogic.com/xdmp/admin" 
      at "/MarkLogic/admin.xqy";

let $config := admin:get-configuration()
return 
  admin:save-configuration(
    admin:database-set-large-size-threshold(
        $config, xdmp:database("myDatabase"),2048)

When the threshold changes, the reindexing process automatically moves binary documents into or out of the Large Data Directory as needed to match the new setting.

Sizing and Scalability of Binary Content

This section covers the following topics:

• Determining the In Memory Tree Size
• Effect of External Binaries on E-node Compressed Tree Cache Size
• Forest Scaling Considerations

For more information on sizing and scalability, see the Scalability, Availability, and Failover Guide and the Query Performance and Tuning Guide.

max(large-size-threshold, largest-expected-non-binary-document)

Selecting a Location For Binary Content

Each forest contains a Large Data Directory that holds the binary contents of all large binary documents in the forest. The default physical location of the Large Data Directory is inside the forest. The location is configurable during forest creation. This flexibility allows different hardware to serve small and large binary documents. The Large Data Directory must be accessible to the server instance containing the forest. to specify an arbitrary location for the Large Data Directory, use the $large-data-directory parameter of admin:forest-create or the large data directory forest configuration setting in the Admin Interface. We will need to document the best practice for configuring forest Large data directories which is to put them somewhere other than the default of /var/opt/MarkLogic. In other words, using non-default directories for forest large data directories is considered a good practice.

The external file associated with an external binary document must be located outside the forest containing the document. The external file must be accessible to any server instance evaluating queries that manipulate the document. That is, the external file path used when creating an external-binary node must be resolvable on any server instance running queries against the document.

External binary files may be shared across a cluster by placing them on a network shared file system, as long as the files are accessible along the same path from any e-node running queries against the external binary documents. The reference fragment containing the associated external-binary node may be located on a remote d-node that does not have access to the external storage.

The diagram below demonstrates sharing external binary content across a cluster with different host configurations. On the left, the evaluator node (e-node) and data node (d-node) are separate hosts. On the right, the same host serves as both an evaluator and data node. The database in both configurations contains an external binary document referencing /images/my.jpg. The JPEG content is stored on shared external storage, accessible to the evaluator nodes through the external file path stored in the external binary document in the database.

Monitoring the Total Size of Large Binary Data in a Forest

Use xdmp:forest-status or the Admin Interface to check the disk space consumed by large binary documents in a forest. The size is reported in megabytes. For more details on MarkLogic Server's monitoring capability, see the Monitoring MarkLogic Guide.

To check the size of the Large Data Directory using the Admin Interface:

1. Open the Admin Interface in your browser. For example, http:yourhost:8001.
2. Click Forests in the left tree menu. The Forest summary is displayed.
3. Click the name of a forest to display the forest configuration page.
4. Click the Status tab at the top to display the forest status page.
5. Observe the Large Data Size status, which reflects the total size of the contents of the large data directory.

The following example uses xdmp:forest-status to retrieve the size of the Large Data Directory:

xquery version "1.0-ml";
declare namespace fs = "http://marklogic.com/xdmp/status/forest";
fn:data(
  xdmp:forest-status(
    xdmp:forest("samples-1"))/fs:large-data-size)

Detecting and Removing Orphaned Binaries

Large and external binary content may require special handling to detect and remove orphaned binary data no longer associated with a document in the database. This section covers the following topics related to managing orphaned binary content:

• Detecting and Removing Orphaned Large Binary Content
• Detecting and Removing Orphaned External Binary Content

xquery version "1.0-ml";

for $fid in xdmp:forests()
  for $orphan in xdmp:get-orphaned-binaries($fid)
  return xdmp:remove-orphaned-binary($fid, $orphan)

xquery version "1.0-ml";
for $doc in fn:collection()/binary()
where xdmp:external-binary-path($doc) = "/external/path/sample.jpg"
return xdmp:document-delete(xdmp:node-uri($doc))

xquery version "1.0-ml";
for $doc in fn:collection()/binary()
where xdmp:binary-is-external($doc)
return
  if (xdmp:filesystem-file-exists(xdmp:external-binary-path($doc)))
  then xdmp:node-uri($doc)
  else ()

Adding Metadata to Binary Documents Using Properties

Small, large, and external binary documents may be annotated with metadata using properties. Any document in the database may have an associated properties document for storing additional XML data. Unlike binary data, properties documents may participate in element indexing. For more information about using properties, see Properties Documents and Directories.

MarkLogic Server offers the XQuery built-in, xdmp:document-filter, and JavaScript method, xdmp.documentFilter, to assist with adding metadata to binary documents. These functions extract metadata and text from binary documents as a node, each of whose child elements represent a piece of metadata. The results may be used as document properties. The text extracted contains little formatting or structure, so it is best used for search, classification, or other text processing.

For example, the following code creates properties corresponding to just the metadata extracted by xdmp:document-filter from a Microsoft Word document:

xquery version "1.0-ml";
let $the-document := "/samples/sample.docx"
return xdmp:document-set-properties(
  $the-document, 
  for $meta in xdmp:document-filter(fn:doc($the-document))//*:meta
  return element {$meta/@name} {fn:string($meta/@content)}
)

The result properties document contains properties such as Author, AppName, and Creation_Date, extracted by xdmp:document-filter:

<prop:properties xmlns:prop="http://marklogic.com/xdmp/property">
  <content-type>application/msword</content-type>
  <filter-capabilities>text subfiles HD-HTML</filter-capabilities>
  <AppName>Microsoft Office Word</AppName>
  <Author>MarkLogic</Author>
  <Company>Mark Logic Corporation</Company>
  <Creation_Date>2011-09-05T16:21:00Z</Creation_Date>
  <Description>This is my comment.</Description>
  <Last_Saved_Date>2011-09-05T16:22:00Z</Last_Saved_Date>
  <Line_Count>1</Line_Count>
  <Paragraphs_Count>1</Paragraphs_Count>
  <Revision>2</Revision>
  <Subject>Creating binary doc props</Subject>
  <Template>Normal.dotm</Template>
  <Typist>MarkLogician</Typist>
  <Word_Count>7</Word_Count>
  <isys>SubType: Word 2007</isys>
  <size>10047</size>
  <prop:last-modified>2011-09-05T09:47:10-07:00</prop:last-modified>
</prop:properties>

Downloading Binary Content With HTTP Range Requests

HTTP applications often use range requests (sometimes called partial GET) to serve large data, such as videos. MarkLogic Server directly supports HTTP range requests for static binary content. Static binary content is binary content stored in the modules database of the App Server. Range requests for dynamic binary content are not directly supported, but you may write application code to service such requests. Dynamic binary content is any binary content generated by your application code.

This section covers the following topics related to serving binary content in response to range requests:

• Responding to Range Requests with Static Binary Content
• Responding to Range Requests with Dynamic Binary Content

GET http://host:8010/images/really_big.jpg

GET http://host:8010/images/really_big.jpg
Range: bytes=0-499

HTTP/1.0 206 Partial Content
Accept-Ranges: bytes
Content-Length: 500
Content-Range: bytes 0-499/3980
Content-Type: image/jpeg

[first 500 bytes of /images/really_big.jpg]

xquery version "1.0-ml";

(: This code assumes a simple range like 1000-2000; your :)
(: application code may support more complex ranges.     :)

let $data := fn:doc(xdmp:get-request-field("uri"))/binary()
let $range := xdmp:get-request-header("Range")
return 
  if ($range)
  then  
    let $range := replace(normalize-space($range), "bytes=", "")
    let $splits := tokenize($range, "-")
    let $start := xs:integer($splits[1])
    let $end := if ($splits[2] eq "")
                then xdmp:binary-size($data)-1
                else xs:integer($splits[2])
    let $ranges  := 
        concat("bytes ", $start, "-", $end, "/",
               xdmp:binary-size($data))
    return (xdmp:add-response-header("Content-Range", $ranges),
            xdmp:set-response-content-type("image/JPEG"),
            xdmp:set-response-code(206, "Partial Content"),
            xdmp:subbinary($data, $start+1, $end - $start + 1))
    else $data

$ curl -r "0-99" http://myhost:1234/fetch-bin.xqy?uri=sample.jpg

HTTP/1.1 206 Partial Content
Content-Range: bytes 0-99/1442323
Content-type: image/JPEG
Server: MarkLogic
Content-Length: 100

[first 100 bytes of sample.jpg]

Creating Binary Email Attachments

To generate an email message with a binary attachment, use xdmp:email and set the content type of the message to multipart/mixed. The following example generates an email message with a JPEG attachment:

xquery version "1.0-ml";

(: generate a random boundary string :)
let $boundary := concat("blah", xdmp:random())
let $newline := "
"
let $content-type := concat("multipart/mixed; boundary=",$boundary)
let $attachment1 := xs:base64Binary(doc("/images/sample.jpeg"))
let $content := concat(
  "--",$boundary,$newline,
  $newline,
  "This is a test email with an image attached.", $newline,
  "--",$boundary,$newline,
  "Content-Type: image/jpeg", $newline,
  "Content-Disposition: attachment; filename=sample.jpeg", $newline,
  "Content-Transfer-Encoding: base64", $newline,
  $newline,
  $attachment1, $newline,
  "--",$boundary,"--", $newline)

return 
  xdmp:email(
  <em:Message 
    xmlns:em="URN:ietf:params:email-xml:" 
    xmlns:rf="URN:ietf:params:rfc822:">
    <rf:subject>Sample Email</rf:subject>
    <rf:from>
      <em:Address>
        <em:name>Myself</em:name>
        <em:adrs>me@somewhere.com</em:adrs>
      </em:Address>
    </rf:from>
    <rf:to>
      <em:Address>
        <em:name>Somebody</em:name>
        <em:adrs>somebody@somewhere.com</em:adrs>
      </em:Address>
    </rf:to>
    <rf:content-type>{$content-type}</rf:content-type>
    <em:content xml:space="preserve">
      {$content}
    </em:content>
  </em:Message>)