Optimize or disable the Prefetch caches

Current version: 10.3

Applies to	Content Delivery, Content Management

The Prefetch caches are initially populated on application startup and continue to be populated during the lifetime of the application. The list of items to prefetch is defined for each database in the configuration files in the <wwwroot>/App_Config/Prefetch/ folder.

Note

Read more about optimizing and disabling the initial population of the Prefetch caches in the Excessive load on the Core database after application restart knowledge base article.

Prefetching too many items increases the load on the SQL server and can degrade application startup time. To avoid this, you can:

Optimize the initial population of the Prefetch caches.
Disable the initial population of the Prefetch caches.

Optimize the initial population of the Prefetch caches

You optimize the initial population of the Prefetch caches by only including the most frequently accessed items.

Use the following elements to determine which items are included:

Element	Description	Multiple elements allowed
`<template>`	This element includes all items based on a specific template.	Yes
`<item>`	This element includes the specified item.	Yes
`<children>`	This element includes the child items of a specified item.	Yes
`<childLimit>`	This element limits the number of child items that can be cached for each parent item.	No

The following is a sample patch file containing the Prefetch caches configuration elements:

RequestResponse

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/"
               xmlns:set="http://www.sitecore.net/xmlconfig/set/"
               xmlns:role="http://www.sitecore.net/xmlconfig/role/">
    <sitecore>
        <databases>
            <database id="web">
                <dataProviders>
                    <param desc="headProvider">
                        <dataProvider param1="$(id)">
                            <prefetch hint="raw:AddPrefetch">
                                <template desc="sample">{<template GUID="">}</template>
                                <item desc="root">{<item GUID="">}</item>
                                <children desc="main sections">{<item GUID="">}</children>
                                <childLimit>100</childLimit>
                            </prefetch>
                        </dataProvider>
                    </param>
                </dataProviders>
            </database>
        </databases>
    </sitecore>
</configuration>

Use groups to split prefetching requests

You can use groups to speed up the initial population of the Prefetch caches and prevent database timeout exceptions.

By default, the initial population of the Prefetch caches runs as a single SQL request. You can split this initial population into several parallel requests by grouping elements.

You can group elements using the group attribute. You can use the group attribute with the template, item, and children attributes.

The elements from the same group and element type are prefetched together. If an element's group attribute is not specified, then the default group is used.

The following is a sample that prefetches the ui group and dictionary group as two separate requests run in parallel:

RequestResponse

<template group="ui" desc="tool button new line">{6400BD3F-E8A1-4C38-8319-131448492439}</template>    
<template group="ui" desc="toolbar">{3A1A3B48-3434-4E5A-8F05-AD6E1687D888}</template>    
<template group="dictionary" desc="dictionary folder">{267D9AC7-5D85-4E9D-AF89-99AB296CC218}</template>    
<template group="dictionary" desc="dictionary entry">{6D1CD897-1936-4A3A-A511-289A94C2A7B1}</template>

Disable the initial population of the Prefetch caches

If you disable the initial population of the Prefetch caches, they are still populated when items are accessed by visitors.

To disable the initial population:

Replace all element under the configuration/sitecore/databases/database/dataProviders/dataProvider/prefetch elements with a <patch:delete /> element.

Add an new <prefetch> element with the following global elements:

Element	Description	Mandatory
`<cacheSize>`	This element configures the maximum initial Prefetch cache size. If it is not specified, it defaults to the value of the `Caching.DefaultDataCacheSize` setting.	No
`<childLimit>`	This element limits the number of child items that can be cached for each parent item.	Yes
`<logStats>`	When this element is set to `true`, advanced diagnostics information is logged as: RequestResponse `Count: <number of added items>, Template: <template GUID>`	Yes

The following is a sample patch file containing the Prefetch caches configuration elements:

RequestResponse

<configuration xmlns:patch="http://www.sitecore.net/xmlconfig/"
               xmlns:set="http://www.sitecore.net/xmlconfig/set/"
               xmlns:role="http://www.sitecore.net/xmlconfig/role/">
    <sitecore>
        <databases>
            <database id="web">
                <dataProviders>
                    <param desc="headProvider">
                        <dataProvider param1="$(id)">
                            <prefetch hint="raw:AddPrefetch">
                                <patch:delete />
                            </prefetch>
                            <prefetch hint="raw:AddPrefetch">
                                <cacheSize>1000MB</cacheSize>
                                <childLimit>100</childLimit>
                                <logStats>false</logStats>
                            </prefetch>
                        </dataProvider>
                    </param>
                </dataProviders>
            </database>
        </databases>
    </sitecore>
</configuration>

Do you have some feedback for us?

If you have suggestions for improving this article,