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Even within a trusted organisation, the flat trust model of memcached may have security implications. For efficient simplicity, all Memcached operations are treated equally. Clients with a valid need for access to low-security entries within the cache gain access to all entries within the cache, even when these are higher-security and that client has no justifiable need for them. If the cache key can be either predicted, guessed or found by exhaustive searching, its cache entry may be retrieved.

Some attempt to isolate setting and reading data may be made in situations such as high volume web publishing. A farm of outward-facing content servers have read access to memcached containing published pages or page components, but no write access. Where new content is published (and is not yet in memcached), a request is instead sent to content generation servers that are not publicly accessible to create the content unit and add it to memcached. The content server then retries to retrieve it and serve it outwards.

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In February 2018, CloudFlare reported that misconfigured memcached servers were used to launch DDoS attacks in large scale.[22] The memcached protocol over UDP has a huge amplification factor, of more than 51000.[23] Victims of the DDoS attacks include GitHub, which was flooded with 1.35 Tbit/s peak incoming traffic.[24]

Currently we have a website running on a Centos 6.5 webserver with Direct Admin. APC was configured in the past and is working nicely, but some reading suggested to also implement memcached to cache some static tables (like for instance menu's).

As of MySQL 5.6, the innoDB tables are compatible with a mysql memcache deamon, so I started off following this guide: -memcached-installing.html.The config script is ran and the deamon is installed.

Since both extensions are called memcached.so, we strongly have the feeling this is the same thing. Are there actually two different things and does Drupal not support the InnoDB memcached deamon, do I need both (php extension to access the mysql extension?), or was this supposed to be working and did we something wrong?

The Memcached interface to InnoDB is a feature of MySQL to support the memcached protocol, yet with InnoDB as the back-end storage. It seems like lot of people have been confused by what this means, so I'll try to explain.

Whereas a real memcached daemon stores data in memory, MySQL stores data persistently in an InnoDB table. PHP applications can read and write data using the memcached extension, as if they're using a standard memcached in-memory store. However, they are really reading and writing rows from the InnoDB table.

This is somewhat slower than standard memcached, because it has the overhead of writing to disk is greater than accessing memory. But it's somewhat faster than using SQL to read and write those rows, because it skips the complexity of the SQL parser and query optimizer.

That's really the new feature in MySQL: to bypass SQL, and give access directly to the InnoDB storage engine through a simple, but familiar interface. They chose memcached on the theory that many developers would be familiar with it and have tools and language support for it already.

memcached is a fully featured Memcached client for Node.js. memcached isbuilt with scaling, high availability and exceptional performance in mind. Weuse consistent hashing to store the data across different nodes. Consistenthashing is a scheme that provides a hash table functionality in a way thatadding or removing a server node does not significantly change the mapping ofthe keys to server nodes. The algorithm that is used for consistent hashing isthe same as libketama.

There are different ways to handle errors for example, when a server becomesunavailable you can configure the client to see all requests to that server ascache misses until it goes up again. It's also possible to automatically removethe affected server from the consistent hashing algorithm or provide memcachedwith a failover server that can take the place of the unresponsive server.

The client is configurable on different levels. There's a global configurationthat you update so all your Memcached clusters will use the same failureconfiguration for example, but it's also possible to overwrite these changes permemcached instance.

.command This is the core functionality of the memcached client. All public API's arerouted through this function. It takes care of the argument validations Serverretrieval ( If the server argument isn't specified ). After all data ready aconnection is asked for the private connect method and the command is writtento the Memcached server.

I have 1 mysql table which is controlled strictly by admin. Data entry is very low but query is high in that table. Since the table will not change content much I was thinking to use mysql query cache with PHP but got confused (when i googled about it) with memcached.

Memcached is a key-value store. Basically it can cache anything if you can turn it into key => value. There are a lot of ways you can implement caching with it. You could query your 30 rows from database, then cache it row by row but I don't see a reason to do that here if you're returning the same set of rows over and over. The most basic example I can think of for memcached is:

But since you're using the same query over and over. Why add the complication when you can let MySQL handle all the caching for you? Remember that if you go with memcached option, you need to setup memcached server as well as implementing logic to check if the result is already in cache or not, or if the records have been changed in the database.

I'm working on some old(ish) software in PHP that maintains a $cache array to reduce the number of SQL queries. I was thinking of just putting memcached in its place and I'm wondering whether or not to get rid of the internal caching. Would there still be a worthwihle performance increase if I keep the internal caching, or would memcached suffice?

2. You don't want it to.

_do_expired_cached_items_get_deleted_from_the_cache?

Having to have a garbage collector that watched items for expiration

would increase the load that memcached put on a system a great deal.Brian.

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If you land here in Oct 2020 because you're getting an error after upgrading and you're using the repository ppa:ondrej/php you need to install the specific version of msgpack because all-of-a-sudden memcached is looking for this shared object.

The ngx_http_memcached_module module is used to obtainresponses from a memcached server.The key is set in the $memcached_key variable.A response should be put in memcached in advance by meansexternal to nginx.

Makes outgoing connections to a memcached server originatefrom the specified local IP address with an optional port (1.11.2).Parameter value can contain variables (1.3.12).The special value off (1.3.12) cancels the effectof the memcached_bind directiveinherited from the previous configuration level, which allows thesystem to auto-assign the local IP address and port.

In order for this parameter to work,it is usually necessary to run nginx worker processes with thesuperuser privileges.On Linux it is not required (1.13.8) as ifthe transparent parameter is specified, worker processesinherit the CAP_NET_RAW capability from the master process.It is also necessary to configure kernel routing tableto intercept network traffic from the memcached server.

Defines a timeout for reading a response from the memcached server.The timeout is set only between two successive read operations,not for the transmission of the whole response.If the memcached server does not transmit anything within this time,the connection is closed.

Sets a timeout for transmitting a request to the memcached server.The timeout is set only between two successive write operations,not for the transmission of the whole request.If the memcached server does not receive anything within this time,the connection is closed.

At peak we've seen 260Gbps of inbound UDP memcached traffic. This is massive for a new amplification vector. But the numbers don't lie. It's possible because all the reflected packets are very large. This is how it looks in tcpdump:

I was surprised to learn that memcached does UDP, but there you go! The protocol specification shows that it's one of the best protocols to use for amplification ever! There are absolutely zero checks, and the data WILL be delivered to the client, with blazing speed! Furthermore, the request can be tiny and the response huge (up to 1MB).

If you are using memcached, please disable UDP support if you are not using it. On memcached startup you can specify --listen 127.0.0.1 to listen only to localhost and -U 0 to disable UDP completely. By default memcached listens on INADDR_ANY and runs with UDP support ENABLED. Documentation:

We've been down this road so many times. DNS, NTP, Chargen, SSDP and now memcached. If you use UDP, you must always respond with strictly a smaller packet size then the request. Otherwise your protocol will be abused. Also remember that people do forget to set up a firewall. Be a nice citizen. Don't invent a UDP-based protocol that lacks authentication of any kind.

It's anyone's guess how large the memcached attacks will become before we clean the vulnerable servers up. There were already rumors of 0.5Tbps amplifications in the last few days, and this is just a start.

Memcached, the most commonly-used production cache backend, does not allowcache keys longer than 250 characters or containing whitespace or controlcharacters, and using such keys will cause an exception. To encouragecache-portable code and minimize unpleasant surprises, the other built-in cachebackends issue a warning (django.core.cache.backends.base.CacheKeyWarning)if a key is used that would cause an error on memcached.

If you are using a production backend that can accept a wider range of keys (acustom backend, or one of the non-memcached built-in backends), and want to usethis wider range without warnings, you can silence CacheKeyWarning withthis code in the management module of one of yourINSTALLED_APPS: e24fc04721