There are presently 4744 active blocks on Wikipedia EN:
On a good day this makes the block list very slow to load. If the servers are
already overloaded, it is basically unusuable.
I think this is because SpecialIpblocklist::wfAddRow calls User::whoIs for each
entry in order to identify the name of the blocking admin on each block. That
means that to load the block list it is presently necessary to make more than
4744 distinct database queries. I would suggest that either Block::enumBlocks be
modified to join on the list of blocking admin usernames, or that the blocklist
be reformated into pages the same way most other query pages are so it only loads
a fraction of the blocks at any one time.
With the continuing war with the Willy on Wheels vandal (see: []), the
block list is only likely to grow and make the problem worse.