How to delete lots of related keys at once

[Clint Webb]

Why is everyone using memcache for the SQL query as a key?  That is what the
query cache on your database is for.  You gain very little doing it this
way, except now you have to manage the invalidation yourself, which the
query-cache does for you.

Anyway, you can set your keys with an expiry so that they dissapear after a
certain time and can be regenerated.  Each site is different, but for any
kind of data that could change, and you dont have an easy way of identifying
the affected keys when it does change, then you should give it an expiry
time.  That way, eventually, changes will be replicated thru the cache as
the keys expire and regenerate.

Namespaces probably isnt what you are looking for.  It merely adds a string
to the begining of the key.  Useful if you are using the same memcache
cluster for multiple applications, but thats about it.  If you normally use
a key of "Article:id=5", but use a namespace of "Supersite-" then internally
your key will now be "Supersite-Article:id=5".

I use namespaces for my sitelogging (web instances write logging info to
cache using incremented keys, external process pulls those log entries out
of cache and puts them in a file).  I have multiple sites use the same
memcache cluster, and the same piece of code, but the sites logs are kept
seperate, and copied out to different files, because when the different
sites (and external processing script) connect to the cache, they use
different namespaces.

On 8/3/07, Jarom Severson <j.severson at yahoo.com> wrote:
>
> My main confusion or concern with memcache is how to
> go about deleting a given set of keys in the
> cache. For instance, we probably have 10-15 pages on
> our site that hit the "articles" tables in our
> database. So, that right there would be 10-15 unique
> key/value pairs in memcache, assuming I store the
> query as the key, and the result set as the value. Now
> add on dynamic search strings, pagination, etc, and
> you've probably got 100 unique key/value pairs in
> memcache, all pertaining to articles.
>
> So my question is, if we want to make sure our site is
> never stale, then we need to invalidate all 100 of
> those keys if someone inserts a new article. Now I'm
> thinking I need to do a search in my keys to find all
> article related keys and invalidate them.
>
> Is the best way to do this then to store ANOTHER key
> value pair which essentially stores all the article
> related keys as its value? So that I can quickly and
> easily invalidate the 100 other keys?
>
> It seems like this might be what "namespaces" are for,
> but I can't understand the example given on the
> memcached FAG page.
>
> Any help and direction in this area would be much
> appreciated, or any other good articles I should read
> that talk about best practices, implementation
> techniques, etc.
>
> thanks in advance.
>
> Jay
>
>


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