[tarantool-patches] [PATCH] iproto: update readahead in existing connections

[Serge Petrenko <sergepetrenko@tarantool.org>]

Iproto connections keep old readahead values for input buffers even
after box.cfg.readahead reconfiguration. This means that for the changes
to take place for the old clients, they have to reconnect. Otherwise
tarantool log will be spammed with 'readahead limit is reached' errors.

To fix this, start updating input buffer size for iproto connections
if needed every time the buffer is empty.

Closes #3958
---
https://github.com/tarantool/tarantool/issues/3958
https://github.com/tarantool/tarantool/tree/sp/gh-3958-iproto-update-readahead

 src/box/iproto.cc               |  8 +++-
 test/box/iproto_stress.result   | 66 +++++++++++++++++++++++++++++++--
 test/box/iproto_stress.test.lua | 40 +++++++++++++++++++-
 3 files changed, 108 insertions(+), 6 deletions(-)

diff --git a/src/box/iproto.cc b/src/box/iproto.cc
index a08c8c5cb..745221841 100644
--- a/src/box/iproto.cc
+++ b/src/box/iproto.cc
@@ -145,7 +145,8 @@ iproto_reset_input(struct ibuf *ibuf)
 	 * move the pos to the start of the input buffer.
 	 */
 	assert(ibuf_used(ibuf) == 0);
-	if (ibuf_capacity(ibuf) < iproto_max_input_size()) {
+	if (ibuf_capacity(ibuf) < iproto_max_input_size() &&
+	    ibuf->start_capacity == iproto_readahead) {
 		ibuf_reset(ibuf);
 	} else {
 		struct slab_cache *slabc = ibuf->slabc;
@@ -670,6 +671,11 @@ iproto_connection_input_buffer(struct iproto_connection *con)
 		 */
 		return NULL;
 	}
+	/* Update buffer size if readahead has changed. */
+	if (new_ibuf->start_capacity != iproto_readahead) {
+		ibuf_destroy(new_ibuf);
+		ibuf_create(new_ibuf, cord_slab_cache(), iproto_readahead);
+	}
 
 	ibuf_reserve_xc(new_ibuf, to_read + con->parse_size);
 	/*
diff --git a/test/box/iproto_stress.result b/test/box/iproto_stress.result
index 4239b49b8..6ced92d70 100644
--- a/test/box/iproto_stress.result
+++ b/test/box/iproto_stress.result
@@ -86,12 +86,72 @@ n_errors -- 0
 ---
 - 0
 ...
-box.schema.user.revoke('guest', 'read,write,execute', 'universe')
+s:drop()
 ---
 ...
-s:drop()
+-- gh-3958 updating box.cfg.readahead doesn't affect existing connections.
+test_run:cmd('restart server default')
+fiber = require('fiber')
+---
+...
+netbox = require('net.box')
+---
+...
+readahead = box.cfg.readahead
+---
+...
+net_msg_max = box.cfg.net_msg_max
+---
+...
+box.cfg{net_msg_max=1000, readahead = 128}
+---
+...
+test_run:cmd('setopt delimiter ";"')
+---
+- true
+...
+function do_call(arg)
+    fiber.sleep(0.1)
+    return arg
+end;
+---
+...
+test_run:cmd('setopt delimiter ""');
+---
+- true
+...
+-- connection is created with small readahead value,
+-- make sure it is updated if box.cfg.readahead is changed.
+c = netbox.connect(box.cfg.listen)
+---
+...
+box.cfg{readahead = 100 * 1024}
+---
+...
+test_run:cmd('setopt delimiter ";"')
+---
+- true
+...
+for i = 1,500 do
+    local pad = string.rep('x', 100)
+    fiber.create(function()
+        for i = 1,10 do
+            c:call('do_call', {pad})
+        end
+    end)
+end;
+---
+...
+test_run:cmd('setopt delimiter ""');
+---
+- true
+...
+test_run:wait_log('default', 'readahead limit is reached', nil, 1.0)
+---
+...
+box.schema.user.revoke('guest', 'read,write,execute', 'universe')
 ---
 ...
-box.cfg{net_msg_max = net_msg_max}
+box.cfg{net_msg_max = net_msg_max, readahead = readahead}
 ---
 ...
diff --git a/test/box/iproto_stress.test.lua b/test/box/iproto_stress.test.lua
index 2f3071450..931e66d59 100644
--- a/test/box/iproto_stress.test.lua
+++ b/test/box/iproto_stress.test.lua
@@ -46,7 +46,43 @@ while n_workers > 0 and attempt < 100 do fiber.sleep(0.1) attempt = attempt + 1
 n_workers -- 0
 n_errors -- 0
 
-box.schema.user.revoke('guest', 'read,write,execute', 'universe')
 s:drop()
 
-box.cfg{net_msg_max = net_msg_max}
+-- gh-3958 updating box.cfg.readahead doesn't affect existing connections.
+test_run:cmd('restart server default')
+fiber = require('fiber')
+netbox = require('net.box')
+
+readahead = box.cfg.readahead
+net_msg_max = box.cfg.net_msg_max
+
+box.cfg{net_msg_max=1000, readahead = 128}
+
+test_run:cmd('setopt delimiter ";"')
+function do_call(arg)
+    fiber.sleep(0.1)
+    return arg
+end;
+test_run:cmd('setopt delimiter ""');
+
+-- connection is created with small readahead value,
+-- make sure it is updated if box.cfg.readahead is changed.
+c = netbox.connect(box.cfg.listen)
+
+box.cfg{readahead = 100 * 1024}
+
+test_run:cmd('setopt delimiter ";"')
+for i = 1,500 do
+    local pad = string.rep('x', 100)
+    fiber.create(function()
+        for i = 1,10 do
+            c:call('do_call', {pad})
+        end
+    end)
+end;
+test_run:cmd('setopt delimiter ""');
+
+test_run:wait_log('default', 'readahead limit is reached', nil, 1.0)
+
+box.schema.user.revoke('guest', 'read,write,execute', 'universe')
+box.cfg{net_msg_max = net_msg_max, readahead = readahead}
-- 
2.17.2 (Apple Git-113)