Hey there. My company writes a lot of social applications, and there is
one operation that is very common, but I don't know if MySQL supports it
in a good way. I thought I'd write to this list for two reasons:
1) Maybe MySQL has a good way to do this, and I just don't know
2) Propose to MySQL developers a simple algorithm which would
greatly improve MySQL support for social networking apps.
Here is the situation. Let's say I have built a social networking
application where people create and edit some item (article, photo,
music mix, whatever). Now, a typical user logs in, and this user has
3000 friends. How can I quickly find all the articles written by this
user's friends, and not just random articles?
Ideally, I would want to write something like this:
SELECT * FROM article WHERE user_id IN (345789, 324875, 398, ...,
basically, execute a query with a huge IN ( ... ). Maybe if this
would exceed the buffer size for the MySQL wire protocol, I would break
up the list into several lists, and execute several queries, and union
the results together myself.
But my point is, this is very common for social networking apps.
Every app wants to show "the X created by your friends", or "friends of
yours (given some list from a social network) who have taken action X".
Here is how I would do it if I had raw access to the MySQL index in
a) Sort the list of entries in the IN, in ascending order.
b) Do *ONE* binary search through the index (assuming it's a BTREE
index) and get them all in one pass. If it's a HASH index or something,
I would have to look up each one individually.
The benefits of this approach would be that this common operation
would be done extremely quickly. If the index fits entirely in memory,
and I just want to get the primary keys (i.e. get the list of friends
who did X), the disk isn't even touched. In addition, for BTREE indexes,
I would just need ONE binary search, because the entries have been
sorted in ascending order.
Does MySQL have something like this? And if not, perhaps you can
add it in the next version? It would really boost MySQL's support for
social networking apps tremendously. Alternative, how can I add this to
my MySQL? Any advice would be appreciated.