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N-MySQL connections shared between M-threads
Posted by: Ruslan Laishev
Date: April 21, 2016 03:50AM

Hello All!

I have a some task where I'm need to implement a "DB connection pool" is shared between multiple threads.

A number of DB-connections is in range 10-20, and a number of threads is 10-100k.

So, in main () I made DB-connection pool with :


...

ASC stmts [] = {
{$ASCINI("SELECT uai_chkauth(?, ?, ?)")},
{$ASCINI("SELECT uai_getstream2(?, ?)")}, /* {$ASCINI("CALL uai_getstream(?, ?, ?)")}
*/
{$ASCINI("SELECT uai_signreq(?, ?)")},
{$ASCINI("SELECT uai_acctng(?, ?, ?, ?)")}, /* rc = (uid, cid, sid, <type>);
type = 1: Start, 2: Stop; */
};
#define QR_ENDOFLIST sizeof(stmts)/sizeof(stmts[0])

typedef struct _db_ctx
{
ENTRY entry; /**< Entry header */
MYSQL * mysql; /** MySQL session context */

MYSQL_STMT * stmt[QR_ENDOFLIST];/* An array of pointer to prepared SQL statments area */
} DB_CTX;

...


/**
* @brief db_init - Initialize a pool of DB-connections context pool
* @param user - DB user name
* @param pass - DB user's password
* @param addr - RDBMS host address
* @param port - RDBMS IP port number
* @param dbname- A DB name
* @param threads - a number of DB-connections to be open
* @return
*/
int __db_init (
char *user,
char *pass,
char *addr,
unsigned port,
char *dbname,
unsigned threads
)
{
unsigned status, on = 1, i, i2, opts = CLIENT_COMPRESS | CLIENT_SSL | CLIENT_REMEMBER_OPTIONS; // | CLIENT_MULTI_RESULTS;

$LOG(STS$K_INFO, "Client version: %s, thread safe = %d",
mysql_get_client_info(), mysql_thread_safe ());


/* Validate size of the DB-connections pool */
threads = $RANGE(threads, 1, MAXDBTHREADS);

if ( mysql_library_init(0, NULL, NULL) )
return $LOG(STS$K_ERROR, "Could not initialize MySQL library");

/* Initialize DB-connection context */
for (i = 0 ; i < threads; i++)
{
if ( !(dbctx.mysql = mysql_init(NULL)) )
break;
if ( !i )
$LOG(STS$K_INFO, "Server version: %d", mysql_get_server_version(dbctx.mysql));

mysql_options(dbctx.mysql, MYSQL_OPT_RECONNECT, &on);

/* Open session to the MySQL */
if ( !mysql_real_connect(dbctx.mysql, addr, user, pass, dbname, port, NULL, opts) )
{
$LOG(STS$K_ERROR, "#%u connect(): %s", i, mysql_error(dbctx.mysql));
break;
}

/* Prepare statements */
for (i2 = 0; i2 < QR_ENDOFLIST; i2++)
{
if ( !(dbctx.stmt[i2] = mysql_stmt_init(dbctx.mysql)) )
return $LOG(STS$K_ERROR, "#%d/%d stmt_init() : %s", i, i2, mysql_error(dbctx.mysql));

if ( mysql_stmt_prepare(dbctx.stmt[i2], $ASCPTR(&stmts[i2]), $ASCLEN(&stmts[i2])) )
return $LOG(STS$K_ERROR, "#%d/%d stmt_prepare('%.*s') : %s", i, i2, $ASC(&stmts[i2]), mysql_error(dbctx.mysql));

$TRACE("#%d/%d , dbctx:%08X, mysql:%08X, stmt = %08X, '%.*s'", i, i2, &dbctx, dbctx.mysql, dbctx.stmt[i2], $ASC(&stmts[i2]));
}
}

$TRACE("%u DB-connections has been requested, %u is opened", threads, i);
threads = i;

/*
* Put has been initialized DB-contexts into the free pool
*/
for (i = 0 ; i < threads; i++)
$INSQTAIL(&free_dbctx, &dbctx, &opts);

if ( dbctxs = threads )
status = $LOG(STS$K_SUCCESS, "%u DB-connection contexts has been initialized", threads);
else status = $LOG(STS$K_FATAL, "No DB-connection contexts has been initialized!!!");

return status;
}

There is two routines to allocate/release DB-connection from pool:

int __db_getctx (DB_CTX **dbctx)
{
int status, count;
struct timespec stime = {0, 0}, etime = {0, 0}, delta = {3, 0};

/* Allocate DB context */
if ( 1 & $REMQHEAD(&free_dbctx, dbctx, &count) )
return SS$_NORMAL;

$TRACE("Cannot allocate DB context, start waiting %d seconds ...", delta);

if ( status = clock_gettime(CLOCK_REALTIME, &stime) )
$LOG(STS$K_ERROR, "clock_gettime -> %d", status);

__starlet$add_time (&stime, &delta, &etime);

pthread_mutex_lock(&dbmtx);

while ( !(1 & (status = $REMQHEAD(&free_dbctx, dbctx, &count))) )
{
status = pthread_cond_timedwait(&dbcond, &dbmtx, &etime);

if ( (status) && (status != ETIMEDOUT) )
status = $LOG( STS$K_ERROR, "pthread_cond_timedwait() -> %d, errno = %d", status, errno);
else if ( status == ETIMEDOUT )
{
status = $LOG( STS$K_ERROR, "Cannot allocate a DB context in %d second!", delta);
break;
}
}

pthread_mutex_unlock(&dbmtx);

return status;
}

int __db_retctx (DB_CTX *dbctx)
{
int status, count;

assert( dbctx );

/* Allocate DB context */
status = $INSQHEAD(&free_dbctx, dbctx, &count);

status = pthread_cond_signal (&dbcond);
status = status ? $LOG(STS$K_ERROR, "pthread_cond_timedwait() -> %d, errno = %d", status, errno)
: SS$_NORMAL;

return status;
}


...

/**
* @brief __db_getstream - Rertrive an information for the stream with a given UID and CID;
* @param uid - UID string, longword unsigned
* @param cid - Content ID, longword unsigned
* @param auth - Authorization URL template, counted string
* @return - condition code: SS$_NORMAL - on successful checking of the credentials
*/
int __db_getstream (
unsigned uid,
unsigned cid,
ASC * auth
)
{
unsigned status = SS$_NORMAL, count;
DB_CTX * dbctx;
MYSQL_BIND in[2] = {0}, out = {0};
MYSQL_RES * res;
MYSQL_STMT * stmt;
char url [ 256 ];

/* Declare input & output parameters ... */
in[0].buffer_type = in[1].buffer_type = MYSQL_TYPE_LONG;
in[0].buffer = &uid; in[1].buffer = &cid;
in[0].is_unsigned = in[1].is_unsigned = 1;
in[0].buffer_length = in[1].buffer_length = 0;

out.buffer_type = MYSQL_TYPE_STRING;
out.buffer_length = sizeof(url);
out.buffer = url;
out.length = &count;

/* Allocate DB context */
if ( !(1 & __db_getctx(&dbctx)) )
return $LOG(STS$K_ERROR, "No free DB context");

#if PREPARED_SQL_STATEMENT
stmt = dbctx->stmt[QR_GETSTREAM];
#else
if ( !(stmt = mysql_stmt_init(dbctx->mysql)) )
return $LOG(STS$K_ERROR, "stmt_init() : %s", mysql_error(dbctx->mysql));

if ( mysql_stmt_prepare(stmt, $ASCPTR(&stmts[QR_GETSTREAM]), $ASCLEN(&stmts[QR_GETSTREAM])) )
return $LOG(STS$K_ERROR, "stmt_prepare('%.*s') : %s", $ASC(&stmts[QR_GETSTREAM]), mysql_error(dbctx->mysql));
#endif
//$TRACE("dbctx:%08X, mysql:%08X, stmt:%08X, UID = %d, CID = %d", dbctx, dbctx->mysql, stmt, uid, cid);

/*
* Bind local variable to input argument of the SQL' routine
*/
if ( mysql_stmt_bind_param(stmt, in) )
status = $LOG(STS$K_ERROR, "dbctx:%08X : %s", dbctx, mysql_stmt_error (stmt));

/*
* Execute preparsed SQL statement, check condition
*/
if ( mysql_stmt_execute(stmt) )
status = $LOG(STS$K_ERROR, "execute(dbctx:%08X, stmt:%08X) : %s", dbctx, stmt, mysql_stmt_error (stmt));
else if ( res = mysql_stmt_result_metadata(stmt) )
{
/*
* We got some result - performs a binding OUTput parameters
* to local variables and fetch it
*/
if ( mysql_stmt_bind_result(stmt, &out) )
status = $LOG(STS$K_ERROR, "bind_result(dbctx:%08X, stmt:%08X) : %s", dbctx, stmt, mysql_stmt_error (stmt));

if ( mysql_stmt_fetch(stmt) )
status = $LOG(STS$K_ERROR, "fetch(dbctx:%08X, stmt:%08X) : %s", dbctx, stmt, mysql_stmt_error (stmt));
else {
status = SS$_NORMAL;
$ASCLEN(auth) = (unsigned char) count;
memcpy($ASCPTR(auth), url, count);
}

mysql_free_result(res);
}
else status = $LOG(STS$K_ERROR, "No data is returned for UID=%d, execute(dbctx:%08X, stmt:%08X)", uid, dbctx, stmt);

#if PREPARED_SQL_STATEMENT
if ( mysql_stmt_reset(stmt) )
#else
if ( mysql_stmt_close(stmt) )
#endif
$LOG(STS$K_ERROR, "stmt_reset/close(dbctx:%08X, stmt:%08X) : %s", dbctx, stmt, mysql_stmt_error (stmt));


/* Release DB context */
if ( !(1 & __db_retctx(dbctx)) )
return $LOG(STS$K_FATAL, "dbctx:%08X : Cannot release!", dbctx);

return status;
}



... Run listing ...


(gdb) run -config=QInfo.cfg
Starting program: /home/sysman/STM-QInfo -config=QInfo.cfg
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7ffff7ffd000
21-04-2016 12:43:20.049 [00c908c0 STM-QINFO-SVC\main\001387] %STMQRSVC-I:Starting ... (built at Apr 21 2016 11:36:03 with CC 4.8.4)

...

21-04-2016 12:43:20.050 [00c908c0 STM-QINFO-DB\__db_init\000155] %STMQRSVC-I:Client version: 6.1.6, thread safe = 1
21-04-2016 12:43:20.050 [00c908c0 STM-QINFO-DB\__db_init\000170] %STMQRSVC-I:Server version: 0
21-04-2016 12:43:20.264 [00c908c0 STM-QINFO-DB\__db_init\000190] #0/0 , dbctx:00C8D940, mysql:00C940D0, stmt = 00CB0950, 'SELECT uai_chkauth(?, ?, ?)'
21-04-2016 12:43:20.317 [00c908c0 STM-QINFO-DB\__db_init\000190] #0/1 , dbctx:00C8D940, mysql:00C940D0, stmt = 00CB2530, 'SELECT uai_getstream2(?, ?)'
21-04-2016 12:43:20.370 [00c908c0 STM-QINFO-DB\__db_init\000190] #0/2 , dbctx:00C8D940, mysql:00C940D0, stmt = 00CB4110, 'SELECT uai_signreq(?, ?)'
21-04-2016 12:43:20.424 [00c908c0 STM-QINFO-DB\__db_init\000190] #0/3 , dbctx:00C8D940, mysql:00C940D0, stmt = 00CB5CF0, 'SELECT uai_acctng(?, ?, ?, ?)'
21-04-2016 12:43:20.654 [00c908c0 STM-QINFO-DB\__db_init\000190] #1/0 , dbctx:00C8D978, mysql:00CB78D0, stmt = 00CC0320, 'SELECT uai_chkauth(?, ?, ?)'
21-04-2016 12:43:20.712 [00c908c0 STM-QINFO-DB\__db_init\000190] #1/1 , dbctx:00C8D978, mysql:00CB78D0, stmt = 00CC1F00, 'SELECT uai_getstream2(?, ?)'
21-04-2016 12:43:20.770 [00c908c0 STM-QINFO-DB\__db_init\000190] #1/2 , dbctx:00C8D978, mysql:00CB78D0, stmt = 00CC3AE0, 'SELECT uai_signreq(?, ?)'
21-04-2016 12:43:20.828 [00c908c0 STM-QINFO-DB\__db_init\000190] #1/3 , dbctx:00C8D978, mysql:00CB78D0, stmt = 00CC56C0, 'SELECT uai_acctng(?, ?, ?, ?)'
21-04-2016 12:43:21.056 [00c908c0 STM-QINFO-DB\__db_init\000190] #2/0 , dbctx:00C8D9B0, mysql:00CC72A0, stmt = 00CCFCF0, 'SELECT uai_chkauth(?, ?, ?)'
21-04-2016 12:43:21.113 [00c908c0 STM-QINFO-DB\__db_init\000190] #2/1 , dbctx:00C8D9B0, mysql:00CC72A0, stmt = 00CD18D0, 'SELECT uai_getstream2(?, ?)'
21-04-2016 12:43:21.171 [00c908c0 STM-QINFO-DB\__db_init\000190] #2/2 , dbctx:00C8D9B0, mysql:00CC72A0, stmt = 00CD34B0, 'SELECT uai_signreq(?, ?)'
21-04-2016 12:43:21.228 [00c908c0 STM-QINFO-DB\__db_init\000190] #2/3 , dbctx:00C8D9B0, mysql:00CC72A0, stmt = 00CD5090, 'SELECT uai_acctng(?, ?, ?, ?)'
21-04-2016 12:43:21.228 [00c908c0 STM-QINFO-DB\__db_init\000194] 3 DB-connections has been requested, 3 is opened
21-04-2016 12:43:21.228 [00c908c0 STM-QINFO-DB\__db_init\000204] %STMQRSVC-S:3 DB-connection contexts has been initialized
21-04-2016 12:43:21.228 [00c908c0 STM-QINFO-SVC\main\001412] Allocated 8192 bytes for index area for 512 streams
21-04-2016 12:43:21.228 [f7ffb700 STM-QINFO-SVC\listener\001015] Starting listener sd = 12 ...
21-04-2016 12:43:21.633 [f7ffb700 STM-QINFO-SVC\listener\001068] %STMQRSVC-I:Open connection from 127.0.0.1:20945, sd = 13.
21-04-2016 12:43:21.633 [f77fa700 STM-QINFO-SVC\processor\000801] [#13] Starting session. Sent initial attributes for authentication ...
21-04-2016 12:43:21.740 [f77fa700 STM-QINFO-SVC\chkauth\000627] %STMQRSVC-S:[#13] UID=316 is authenticated.
21-04-2016 12:43:21.740 [f77fa700 STM-QINFO-SVC\processor\000863] %STMQRSVC-S:[#13] Open session for UID=316.
STM-QInfo: ../STM-QInfo/STM-QInfo-DB.c:121: __db_retctx: Assertion `dbctx' failed.
[New LWP 12658]

Program received signal SIGABRT, Aborted.
[Switching to LWP 12658]
0x0000000000617079 in raise ()
(gdb) back
#0 0x0000000000617079 in raise ()
#1 0x00000000005a1e98 in abort ()
#2 0x000000000059c7e4 in __assert_fail_base ()
#3 0x000000000059c83e in __assert_fail ()
#4 0x000000000040a45f in __db_retctx ()
#5 0x000000000040b18b in __db_getstream ()
#6 0x0000000000407447 in regcid ()
#7 0x000000000040905c in processor ()
#8 0x000000000040cfd2 in start_thread ()
#9 0x00000000005f4749 in clone ()
(gdb)



So, I'm puzzled for now: may be I made something wrong at initializition time or at MySQL API routines ?


Thanks in advance.

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N-MySQL connections shared between M-threads
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