The Traffic Server cache consists of a high-speed object database called the object store that indexes objects according to URLs and their associated headers.
This chapter discusses the following topics:
The Traffic Server cache consists of a high-speed object database called the object store. The object store indexes objects according to URLs and associated headers. This enables Traffic Server to store, retrieve, and serve not only web pages, but also parts of web pages - which provides optimum bandwidth savings. Using sophisticated object management, the object store can cache alternate versions of the same object (versions may differ because of dissimilar language or encoding types). It can also efficiently store very small and very large documents, thereby minimizing wasted space. When the cache is full, Traffic Server removes stale data to ensure the most requested objects are kept readily available and fresh.
Traffic Server is designed to tolerate total disk failures on any of the cache disks. If the disk fails completely, then Traffic Server marks the entire disk as corrupt and continues using the remaining disks. An alarm is then created to indicate which disk failed. If all of the cache disks fail, then Traffic Server goes into proxy-only mode.
You can perform the following cache configuration tasks:
Traffic Server maintains a small RAM cache of extremely popular objects. This RAM cache serves the most popular objects as quickly as possible and reduces load on disks, especially during temporary traffic peaks. You can configure the RAM cache size to suit your needs, as described in Changing the Size of the RAM Cache below.
Traffic Server provides a dedicated RAM cache for fast retrieval of popular small objects. The default RAM cache size is automatically calculated based on the number and size of the cache partitions you have configured. If you've partitioned your cache according to protocol and/or hosts, then the size of the RAM cache for each partition is proportional to the size of that partition.
You can increase the RAM cache size for better cache hit performance. However, if you increase the size of the RAM cache and observe a decrease in performance (such as increased latencies), then it's possible that the operating system requires more memory for network resources. In such instances, you should return the RAM cache size to its previous value.
records.config
file located in the Traffic Server config
directory. Variable | Description |
---|---|
proxy.config.cache.ram_cache.size |
Set this variable to specify the size of the RAM cache. The default value of -1 means that the RAM cache is automatically sized at approximately 1MB per gigabyte of disk. |
records.config
file. start_traffic_server
command (refer to Starting Traffic Server).
You can increase or reduce the total amount of disk space allocated to the cache without clearing the content. To check the size of the cache (in bytes), enter the command traffic_line -r proxy.process.cache.bytes_total
.
To increase the total amount of disk space allocated to the cache on existing disks or to add new disks to a Traffic Server node, follow the steps below:
storage.config
file: increase the amount of disk space allocated to the cache on existing disks or describe the new hardware you are adding (refer to storage.config)./etc/rc.d/init.d/traffic_server
file to add a raw disk binding. Instructions for adding a raw disk binding are located in the Traffic Server storage.config
file. To reduce the total amount of disk space allocated to the cache on an existing disk or to remove disks from a Traffic Server node, follow the steps below:
storage.config
file: reduce the amount of disk space allocated to the cache on existing disks or delete the reference to the hardware you're removing (refer to storage.config). /etc/rc.d/init.d/traffic_server
file to remove the raw disk binding for the disk. IMPORTANT: In the storage.config
file, a formatted or raw disk must be at least 128 MB.
You can manage your cache space more efficiently and restrict disk usage by creating cache partitions with different sizes for specific protocols. You can further configure these partitions to store data from specific origin servers and/or domains. The partition configuration must be the same on all nodes in a cluster.
You can create separate partitions for your cache that vary in size to store content according to protocol. This ensures that a certain amount of disk space is always available for a particular protocol. Traffic Server currently supports the http partition type for HTTP objects.
partition.config
file located in the Traffic Server config
directory. partition.config
file. After you've configured your cache partitions based on protocol, you can make changes to the configuration at any time. Before making changes, note the following:
After you have partitioned the cache according to size and protocol, you can assign the partitions you created to specific origin servers and/or domains. You can assign a partition to a single origin server or to multiple origin servers. However, if a partition is assigned to multiple origin servers, then there is no guarantee on the space available in the partition for each origin server. Content is stored in the partition according to popularity. In addition to assigning partitions to specific origin servers and domains, you must assign a generic partition to store content from all origin servers and domains that are not listed. This generic partition is also used if the partitions for a particular origin server or domain become corrupt. If you do not assign a generic partition, then Traffic Server will run in proxy-only mode.
Note: You do not need to stop Traffic Server before you assign partitions to particular hosts or domains. However, this type of configuration is time-consuming and can cause a spike in memory usage. Therefore, it's best to configure partition assignment during periods of low traffic.
hosting.config
file located in the Traffic Server config
directory. hosting.config
file. bin
directory. traffic_line -x
to apply the configuration changes. By default, Traffic Server allows objects of any size to be cached. You can change the default behavior and specify a size limit for objects in the cache via the steps below:
records.config
file located in the Traffic Server config
directory. Variable | Description |
---|---|
proxy.config.cache.max_doc_size |
Set this variable to specify the maximum size allowed for objects in the cache in bytes. Enter 0 (zero) if you do not want a size limit. |
records.config
file. bin
directory. traffic_line -x
to apply the configuration changes. When you clear the cache, you remove all data from the entire cache - including data in the host database. You should clear the cache before performing certain cache configuration tasks, such as partitioning. You cannot clear the cache when Traffic Server is running.
traffic_server -Cclear
clear
command deletes all data in the object store and the host database. Traffic Server does not prompt you to confirm the deletion. Traffic Server accepts the custom HTTP request method PURGE
when removing a specific object from cache. If the object is found in the cache and is successfully removed, then Traffic Server responds with a 200 OK
HTTP message; otherwise, a 404 File Not Found
message is returned.
In the following example, Traffic Server is running on the domain example.com
and you want to remove the image remove_me.jpg
from cache:
$ curl -X PURGE -v "http://example.com/remove_me.jpg"
* About to connect() to example.com port 80 (#0)
* Trying 192.0.32.11... connected
* Connected to example.com (192.0.32.11) port 80 (#0)
> PURGE /remove_me.jpg HTTP/1.1
> User-Agent: curl/7.19.7
> Host: example.com
> Accept: */*
>
< HTTP/1.1 200 Ok
< Date: Thu, 08 Jan 2010 20:32:07 GMT
< Connection: keep-alive
The next time Traffic Server receives a request for the removed object, it will contact the origin server to retrieve it (i.e., it has been purged from the Traffic Server cache).
Note: The procedure above only removes an object from a specific Traffic Server cache. Users may still see the old (removed) content if it was cached by intermediary caches or by the end-users' web browser.
Traffic Server provides a Cache Inspector utility that enables you to view, delete, and invalidate URLs in the cache (HTTP only). The Cache Inspector utility is a powerful tool that's capable of deleting all the objects in your cache; therefore, make sure that only authorized administrators are allowed to access this utility. To control which hosts have access via the mgmt_allow.config
file, see Controlling Host Access to Traffic Manager.
To access the Cache Inspector utility, follow the steps below:
records.config
file located in the Traffic Server config
directory. CONFIG proxy.config.http_ui_enabled INT 1
remap.config
to expose the URL. map http://yourhost.com/myCI http://{cache} @action=allow @src_ip=corp_internal_address
bin
directory, enter the following command to re-read the configuration file:traffic_line -x
http://{cache}
The Cache page provides several options that enable you to view and delete the contents of your cache:
http://www.dianes.com:
http://www.dianes.com/.*\.html$
html
: http://.*\.html$
Note: Only one administrator should delete and invalidate cache entries from the Cache page at any point in time. Changes made by multiple administrators at the same time can lead to unpredictable results.