SharePoint Caching – BLOB

The BLOB cache addresses this aspect of files stored in SharePointServer by
caching the content on the front-end web servers.
By storing files in SharePoint Server but caching them by using the BLOB cache,
page assets can be served quickly and centrally managed at the same time.
BLOB caching is most useful in the following scenarios:
o Frequently accessed page resources such as JavaScript, CSS and page images
o Rich media, especially larger files, such as videos

BLOB caching is less useful in the following scenarios:
o Files that are infrequently accessed
o Files that are modified frequently
To add a new file, the BLOB cache pays a first hit penalty of around five times more requests
to SQL Server (SQL Server round trips) than with the BLOB cached disabled.
These extra round trips are to fetch permission information and other metadata so
the cache can serve the file securely

Operation Effect on BLOB Cache
Editing a file that is BLOB cached 
 The cached file is removed from the cache.
Deleting a file that is BLOB cached 
 The cached file is removed from the cache.
Deleting a file that is not BLOB cached 
 All cached files in the list containing the file that was deleted will be removed from the cache
Deleting a folder in a list 
 All cached files in the list containing the folder that was deleted will be removed from the cache
Renaming or Deleting a list 
 All cached files that were in the list will be removed from the cache
Making any changes to a list
• Permissions
• Title, or Description
• Adding or Removing Content Types 
 All cached files that were in the list will be removed from the cache
Renaming or Deleting a web 
 All cached entries in the web are removed from the cache
Adding or removing permissions to a web, changing inheritance, adding, updating, or deleting roles 
 All cached entries in the web are removed from the cache
Deleting a site collection 
 All cached entries contained in the site collection are removed from the cache
Modifying User Policy on the web
 Entire cache is abandoned, a new cache folder is started
2. OUTPUT Cache

    In SharePoint Server only Publishing  pages can be cached in the output cache.
    When a Publishing page is rendered, the Publishing feature assembles the page dynamically.
    To do this, Publishing must first fetch the page layout and then fetch the contents
    of the page. Both of these operations incur SQL Server round trips that affect throughput and
    latency. To increase throughput and scalability,
    Publishing pages can use the output cache so that pages aren’t rendered on each
    request.
The cache is configured per site collection. 
Here it can be enabled and cache profiles – which control cache behavior – can be configured.

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