tree acc50f4734685af7fa99bba3d95b40f459fefcee
parent 2cf5e5c448cd9bbf21f86282a6d08d82361ebe39
author Di Xiao <xiaodi.larry@gmail.com> 1496270428 -0700
committer Di Xiao <dixiao@google.com> 1500416016 +0000

spanner: add session pool maintainer to maintain the session pool size

The session pool maintainer will compute sessionsToKeep from the
SessionPoolConfig and by keeping the MaxSessionInUse over a period of
time. And try to keep the session pool size.

Breaking:
- Memove MaxSessionAge, we are deprecating MaxSessionAge in favor of
session pool maintainer.
Misc:
- Use sessions in round robin.
- Set default maxSessionAge.
- Set tests to run in parallel.
- Add closeCh for faster teardown.
Fix:
- Update session creation time on refresu.

Change-Id: I7ffeb8f2e9a6ddfdaaf5a62ff634556f379103f7
Reviewed-on: https://code-review.googlesource.com/14210
Reviewed-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Vikas Kedia <vikask@google.com>