Optimize number of realloc syscall during multi/exec flow (#10921)

## Issue
During the MULTI/EXEC flow, each command gets queued until the `EXEC`
command is received and during this phase on every command queue, a
`realloc` is being invoked. This could be expensive based on the realloc
behavior (if copy to a new memory location). 


## Solution
In order to reduce the no. of syscall, couple of optimization I've used.

1. By default, reserve memory for atleast two commands. `MULTI/EXEC` for a
single command doesn't have any significance. Hence, I believe customer wouldn't use it.
2. For further reservation, increase the memory allocation in exponent growth (power of 2).
This reduces the no. of `realloc` call from `N` to `log(N)` times.

## Other changes:

* Include multi exec queued command array in client memory consumption calculation
(affects client eviction too)

0 files changed, 0 insertions, 0 deletions