Tendermint version (use tendermint version or git rev-parse --verify HEAD if installed from source):
before a91680e

What happened:
When I use a bot to make lots of events subscriptions to a node, I noticed that there is a huge increasing memory usage.
Then I checked the code, and I found there is an unreasonable initial slice with the math.MaxInt16 length.

For almost over ten thousand subscription clients, the node will take over 25 GB memory

What you expected to happen:
I think it is better to lower the initial length, such as 16 (the length of most subscription types I tested are only using less than 16 )

Have you tried the latest version: yes/no
no

How to reproduce it (as minimally and precisely as possible):

• run a local node
• make many subscriptions