[PATCH v2 0/4] IProto fixes and iproto_msg_max option

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Branch: http://github.com/tarantool/tarantool/tree/gh-3320-config-msg-max
Issue: https://github.com/tarantool/tarantool/issues/3320

IPROTO_MSG_MAX is a constant that restricts count of requests in fly. It allows
to do not produce too many fibers in TX thread, that would lead to too big
overhead on fibers switching, their stack storing.

But some users have powerful metal on which Tarantool IPROTO_MSG_MAX constant is
not serious, or they want to run more long-poll requests. The patch exposes it
as a configuration runtime parameter.

'iproto_msg_max' is its name. If a user sees that IProto thread is stuck due to
too many requests, it can change iproto_msg_max in runtime, and IProto thread
immediately starts processing pending requests.

'iproto_msg_max' can be decreased, but obviously it can not stop already runned
requests, so if now in IProto thread request count is > new 'iproto_msg_max'
value, then it takes some time until some requests will be finished.

Maximal IProto message count is very linked with TX fiber pool size, that limits
count of fibers produced by remote clients, and transactions. Now it is
configurable too.

In the same patchset a bug is fixed with incorrect discarding long-poll requests
input. Discard just calls iproto_resume() trying to notify libev, that is can
get new data. But is makes no sense, because iproto_resume() continues only
connections stopped due to reached limit of maximal requests in fly, but not
connections whose buffer is overflowed. Such stopped connections can be
continued only after a request is complete.

To continue read from the connection whose buffer was freed by discarding
long-poll it is necessary to explicitly feed to it EV_READ event. On this event iproto_connection_on_input will read a blocked data if it exists.

Another fixed bug is unstoppable batching ignoring the message limit on IProto
requests.

Vladislav Shpilevoy (4):
  iproto: fix error with input discarding
  iproto: fix error with unstoppable batching
  iproto: allow to configure IPROTO_MSG_MAX
  Allow to configure TX fiber pool size

 src/box/box.cc                  |  16 +-
 src/box/box.h                   |   1 +
 src/box/iproto.cc               | 111 ++++++++++----
 src/box/iproto.h                |   3 +
 src/box/lua/cfg.cc              |  12 ++
 src/box/lua/load_cfg.lua        |   5 +
 src/fiber_pool.h                |   6 +-
 test/app-tap/init_script.result |  73 ++++-----
 test/box/admin.result           |   2 +
 test/box/cfg.result             |  27 ++++
 test/box/cfg.test.lua           |  10 ++
 test/box/fat_tx.lua             |  30 ++++
 test/box/request_limit.result   | 321 ++++++++++++++++++++++++++++++++++++++++
 test/box/request_limit.test.lua | 155 +++++++++++++++++++
 14 files changed, 704 insertions(+), 68 deletions(-)
 create mode 100644 test/box/fat_tx.lua
 create mode 100644 test/box/request_limit.result
 create mode 100644 test/box/request_limit.test.lua

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