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Bug#14003080:65104: MAX_USER_CONNECTIONS WITH PROCESSLIST EMPTY

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Analysis:
-------------
If server is started with limit of MAX_CONNECTIONS and 
MAX_USER_CONNECTIONS then only MAX_USER_CONNECTIONS of any particular
users can be connected to server and total MAX_CONNECTIONS of client can
be connected to server.

Server maintains a counter for total CONNECTIONS and total CONNECTIONS 
from particular user.

Here, MAX_CONNECTIONS of connections are created to server. Out of this
MAX_CONNECTIONS, connections from particular user (say USER1) are
also created. The connections from USER1 is lesser than 
MAX_USER_CONNECTIONS. After that there was one more connection request from
USER1. Since USER1 can still create connections as he havent reached
MAX_USER_CONNECTIONS, server increments counter of CONNECTIONS per user.
As server already has MAX_CONNECTIONS of connections, next check to total
CONNECTION count fails. In this case control is returned WITHOUT 
decrementing the CONNECTIONS per user. So the counter per user CONNECTIONS goes
on incrementing for each attempt until current connections are closed. 
And because of this counter per CONNECTIONS reached MAX_USER_CONNECTIONS. 
So, next connections form USER1 user always returns with MAX_USER_CONNECTION 
limit error, even when total connection to sever are less than MAX_CONNECTIONS.

Fix:
-------------
This issue is occurred because of not handling counters properly in the
server. Changed the code to handle per user connection counters properly.
This commit is contained in:
Praveenkumar Hulakund
2012-05-28 11:14:43 +05:30
parent 1c1b16e304
commit ca9a3a8915
7 changed files with 200 additions and 73 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
sql/sql_parse.cc
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@ -949,7 +949,8 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
uint save_db_length= thd->db_length;
char *save_db= thd->db;
USER_CONN *save_user_connect= thd->user_connect;
USER_CONN *save_user_connect=
const_cast<USER_CONN*>(thd->get_user_connect());
Security_context save_security_ctx= *thd->security_ctx;
CHARSET_INFO *save_character_set_client=
thd->variables.character_set_client;
@ -964,7 +965,7 @@ bool dispatch_command(enum enum_server_command command, THD *thd,
{
my_free(thd->security_ctx->user);
*thd->security_ctx= save_security_ctx;
thd->user_connect= save_user_connect;
thd->set_user_connect(save_user_connect);
thd->reset_db (save_db, save_db_length);
thd->variables.character_set_client= save_character_set_client;
thd->variables.collation_connection= save_collation_connection;
@ -5583,7 +5584,7 @@ void mysql_parse(THD *thd, char *rawbuf, uint length,
if (!err)
{
#ifndef NO_EMBEDDED_ACCESS_CHECKS
if (mqh_used && thd->user_connect &&
if (mqh_used && thd->get_user_connect() &&
check_mqh(thd, lex->sql_command))
{
thd->net.error = 0;