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mariadb/sql/semisync_master.cc
Brandon Nesterenko 75c7c6dc39 MDEV-33551: Semi-sync Wait Point AFTER_COMMIT Slow on Workloads with Heavy Concurrency 
When using semi-sync replication with
rpl_semi_sync_master_wait_point=AFTER_COMMIT, the performance of the
primary can significantly reduce compared to AFTER_SYNC's
performance for workloads with many concurrent users executing
transactions. This is because all connections on the primary share
the same cond_wait variable/mutex pair, so any time an ACK is
received from a replica, all waiting connections are awoken to check
if the ACK was for itself, which is done in mutual exclusion.

This patch changes this such that the waiting THD will use its own
local condition variable, and the ACK receiver thread only signals
connections which have been ACKed for wakeup. That is, the
THD::LOCK_wakeup_ready condition variable is re-used for this
purpose, and the Active_tranx queue nodes are extended to hold the
waiting thread, so it can be signalled once ACKed.

Additionally:

 1)  Removed part of MDEV-11853 additions, which allowed suspended
connection threads awaiting their semi-sync ACKs to live until their
ACKs had been received. This part, however, wasn't needed.  That is,
all that was needed was for the Ack_thread to survive.  So now the
connection threads are killed during phase 1. Thereby
THD::is_awaiting_semisync_ack, and all its related code was removed.

 2) COND_binlog_send is repurposed to signal on the condition when
Active_tranx is emptied during clear_active_tranx_nodes.

 3) At master shutdown (when waiting for slaves), instead of the
main loop individually waiting for each ACK, await_slave_reply()
(renamed await_all_slave_replies()) just waits once for the
repurposed COND_binlog_send to signal it is empty.

 4) Test rpl_semi_sync_shutdown_await_ack is updates as following:
   4.1) Added test case (adapted from Kristian Nielsen) to ensure
that if a thread awaiting its ACK is killed while SHUTDOWN WAIT FOR
ALL SLAVES is issued, the primary will still wait for the ACK from
the killed thread.
   4.2) As connections which by-passed phase 1 of thread killing no
longer are delayed for kill until phase 2, we can no longer query
yes/no tx after receiving an ACK/timeout. The check for these
variables is removed.
   4.3) Comment descriptions are updated which mention that the
connection is alive; and adjusted to be the Ack_thread.

Reviewed By:
============
Kristian Nielsen <knielsen@knielsen-hq.org>
2024-03-21 08:42:18 -06:00

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/* Copyright (C) 2007 Google Inc.
Copyright (c) 2008, 2013, Oracle and/or its affiliates.
Copyright (c) 2011, 2022, MariaDB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
#include <my_global.h>
#include "semisync_master.h"
#include <algorithm>
#include <mysql_com.h>
#define TIME_THOUSAND 1000
#define TIME_MILLION 1000000
#define TIME_BILLION 1000000000
/* This indicates whether semi-synchronous replication is enabled. */
my_bool rpl_semi_sync_master_enabled= 0;
unsigned long long rpl_semi_sync_master_request_ack = 0;
unsigned long long rpl_semi_sync_master_get_ack = 0;
my_bool rpl_semi_sync_master_wait_no_slave = 1;
my_bool rpl_semi_sync_master_status = 0;
ulong rpl_semi_sync_master_wait_point =
SEMI_SYNC_MASTER_WAIT_POINT_AFTER_STORAGE_COMMIT;
ulong rpl_semi_sync_master_timeout;
ulong rpl_semi_sync_master_trace_level;
ulong rpl_semi_sync_master_yes_transactions = 0;
ulong rpl_semi_sync_master_no_transactions = 0;
ulong rpl_semi_sync_master_off_times = 0;
ulong rpl_semi_sync_master_timefunc_fails = 0;
ulong rpl_semi_sync_master_wait_timeouts = 0;
ulong rpl_semi_sync_master_wait_sessions = 0;
ulong rpl_semi_sync_master_wait_pos_backtraverse = 0;
ulong rpl_semi_sync_master_avg_trx_wait_time = 0;
ulonglong rpl_semi_sync_master_trx_wait_num = 0;
ulong rpl_semi_sync_master_avg_net_wait_time = 0;
ulonglong rpl_semi_sync_master_net_wait_num = 0;
ulong rpl_semi_sync_master_clients = 0;
ulonglong rpl_semi_sync_master_net_wait_time = 0;
ulonglong rpl_semi_sync_master_trx_wait_time = 0;
Repl_semi_sync_master repl_semisync_master;
Ack_receiver ack_receiver;
/*
structure to save transaction log filename and position
*/
typedef struct Trans_binlog_info {
my_off_t log_pos;
char log_file[FN_REFLEN];
} Trans_binlog_info;
static int get_wait_time(const struct timespec& start_ts);
static ulonglong timespec_to_usec(const struct timespec *ts)
{
return (ulonglong) ts->tv_sec * TIME_MILLION + ts->tv_nsec / TIME_THOUSAND;
}
int signal_waiting_transaction(THD *waiting_thd, const char *binlog_file,
my_off_t binlog_pos)
{
/*
It is possible that the connection thd waiting for an ACK was killed. In
such circumstance, the connection thread will nullify the thd member of its
Active_tranx node. So before we try to signal, ensure the THD exists.
*/
if (waiting_thd)
mysql_cond_signal(&waiting_thd->COND_wakeup_ready);
return 0;
}
/*******************************************************************************
*
* <Active_tranx> class : manage all active transaction nodes
*
******************************************************************************/
Active_tranx::Active_tranx(mysql_mutex_t *lock,
mysql_cond_t *cond,
ulong trace_level)
: Trace(trace_level), m_allocator(max_connections),
m_num_entries(max_connections << 1), /* Transaction hash table size
* is set to double the size
* of max_connections */
m_lock(lock),
m_cond_empty(cond)
{
/* No transactions are in the list initially. */
m_trx_front = NULL;
m_trx_rear = NULL;
/* Create the hash table to find a transaction's ending event. */
m_trx_htb = new Tranx_node *[m_num_entries];
for (int idx = 0; idx < m_num_entries; ++idx)
m_trx_htb[idx] = NULL;
#ifdef EXTRA_DEBUG
sql_print_information("Semi-sync replication initialized for transactions.");
#endif
}
Active_tranx::~Active_tranx()
{
delete [] m_trx_htb;
m_trx_htb = NULL;
m_num_entries = 0;
}
unsigned int Active_tranx::calc_hash(const unsigned char *key, size_t length)
{
unsigned int nr = 1, nr2 = 4;
/* The hash implementation comes from calc_hashnr() in mysys/hash.c. */
while (length--)
{
nr ^= (((nr & 63)+nr2)*((unsigned int) (unsigned char) *key++))+ (nr << 8);
nr2 += 3;
}
return((unsigned int) nr);
}
unsigned int Active_tranx::get_hash_value(const char *log_file_name,
my_off_t log_file_pos)
{
unsigned int hash1 = calc_hash((const unsigned char *)log_file_name,
strlen(log_file_name));
unsigned int hash2 = calc_hash((const unsigned char *)(&log_file_pos),
sizeof(log_file_pos));
return (hash1 + hash2) % m_num_entries;
}
int Active_tranx::compare(const char *log_file_name1, my_off_t log_file_pos1,
const char *log_file_name2, my_off_t log_file_pos2)
{
int cmp = strcmp(log_file_name1, log_file_name2);
if (cmp != 0)
return cmp;
if (log_file_pos1 > log_file_pos2)
return 1;
else if (log_file_pos1 < log_file_pos2)
return -1;
return 0;
}
int Active_tranx::insert_tranx_node(THD *thd_to_wait,
const char *log_file_name,
my_off_t log_file_pos)
{
Tranx_node *ins_node;
int result = 0;
unsigned int hash_val;
DBUG_ENTER("Active_tranx:insert_tranx_node");
ins_node = m_allocator.allocate_node();
if (!ins_node)
{
sql_print_error("%s: transaction node allocation failed for: (%s, %lu)",
"Active_tranx:insert_tranx_node",
log_file_name, (ulong)log_file_pos);
result = -1;
goto l_end;
}
/* insert the binlog position in the active transaction list. */
strncpy(ins_node->log_name, log_file_name, FN_REFLEN-1);
ins_node->log_name[FN_REFLEN-1] = 0; /* make sure it ends properly */
ins_node->log_pos = log_file_pos;
ins_node->thd= thd_to_wait;
if (!m_trx_front)
{
/* The list is empty. */
m_trx_front = m_trx_rear = ins_node;
}
else
{
int cmp = compare(ins_node, m_trx_rear);
if (cmp > 0)
{
/* Compare with the tail first. If the transaction happens later in
* binlog, then make it the new tail.
*/
m_trx_rear->next = ins_node;
m_trx_rear = ins_node;
}
else
{
/* Otherwise, it is an error because the transaction should hold the
* mysql_bin_log.LOCK_log when appending events.
*/
sql_print_error("%s: binlog write out-of-order, tail (%s, %lu), "
"new node (%s, %lu)", "Active_tranx:insert_tranx_node",
m_trx_rear->log_name, (ulong)m_trx_rear->log_pos,
ins_node->log_name, (ulong)ins_node->log_pos);
result = -1;
goto l_end;
}
}
hash_val = get_hash_value(ins_node->log_name, ins_node->log_pos);
ins_node->hash_next = m_trx_htb[hash_val];
m_trx_htb[hash_val] = ins_node;
DBUG_PRINT("semisync", ("%s: insert (%s, %lu) in entry(%u)",
"Active_tranx:insert_tranx_node",
ins_node->log_name, (ulong)ins_node->log_pos,
hash_val));
l_end:
DBUG_RETURN(result);
}
bool Active_tranx::is_tranx_end_pos(const char *log_file_name,
my_off_t log_file_pos)
{
DBUG_ENTER("Active_tranx::is_tranx_end_pos");
unsigned int hash_val = get_hash_value(log_file_name, log_file_pos);
Tranx_node *entry = m_trx_htb[hash_val];
while (entry != NULL)
{
if (compare(entry, log_file_name, log_file_pos) == 0)
break;
entry = entry->hash_next;
}
DBUG_PRINT("semisync", ("%s: probe (%s, %lu) in entry(%u)",
"Active_tranx::is_tranx_end_pos",
log_file_name, (ulong)log_file_pos, hash_val));
DBUG_RETURN(entry != NULL);
}
void Active_tranx::clear_active_tranx_nodes(
const char *log_file_name, my_off_t log_file_pos,
active_tranx_action pre_delete_hook)
{
Tranx_node *new_front;
DBUG_ENTER("Active_tranx::::clear_active_tranx_nodes");
new_front= m_trx_front;
while (new_front)
{
if ((log_file_name != NULL) &&
compare(new_front, log_file_name, log_file_pos) > 0)
break;
pre_delete_hook(new_front->thd, new_front->log_name, new_front->log_pos);
new_front = new_front->next;
}
if (new_front == NULL)
{
/* No active transaction nodes after the call. */
/* Clear the hash table. */
memset(m_trx_htb, 0, m_num_entries * sizeof(Tranx_node *));
m_allocator.free_all_nodes();
/* Clear the active transaction list. */
if (m_trx_front != NULL)
{
m_trx_front = NULL;
m_trx_rear = NULL;
}
DBUG_PRINT("semisync", ("%s: cleared all nodes",
"Active_tranx::::clear_active_tranx_nodes"));
}
else if (new_front != m_trx_front)
{
Tranx_node *curr_node, *next_node;
/* Delete all transaction nodes before the confirmation point. */
#ifdef DBUG_TRACE
int n_frees = 0;
#endif
curr_node = m_trx_front;
while (curr_node != new_front)
{
next_node = curr_node->next;
#ifdef DBUG_TRACE
n_frees++;
#endif
/* Remove the node from the hash table. */
unsigned int hash_val = get_hash_value(curr_node->log_name, curr_node->log_pos);
Tranx_node **hash_ptr = &(m_trx_htb[hash_val]);
while ((*hash_ptr) != NULL)
{
if ((*hash_ptr) == curr_node)
{
(*hash_ptr) = curr_node->hash_next;
break;
}
hash_ptr = &((*hash_ptr)->hash_next);
}
curr_node = next_node;
}
m_trx_front = new_front;
m_allocator.free_nodes_before(m_trx_front);
DBUG_PRINT("semisync", ("%s: cleared %d nodes back until pos (%s, %lu)",
"Active_tranx::::clear_active_tranx_nodes",
n_frees,
m_trx_front->log_name, (ulong)m_trx_front->log_pos));
}
/*
m_cond_empty aliases Repl_semi_sync_master::COND_binlog, which holds the
condition variable to notify that we have cleared all nodes, e.g. used by
SHUTDOWN WAIT FOR ALL SLAVES.
*/
if (is_empty())
mysql_cond_signal(m_cond_empty);
DBUG_VOID_RETURN;
}
void Active_tranx::unlink_thd_as_waiter(const char *log_file_name,
my_off_t log_file_pos)
{
DBUG_ENTER("Active_tranx::unlink_thd_as_waiter");
mysql_mutex_assert_owner(m_lock);
unsigned int hash_val = get_hash_value(log_file_name, log_file_pos);
Tranx_node *entry = m_trx_htb[hash_val];
while (entry != NULL)
{
if (compare(entry, log_file_name, log_file_pos) == 0)
break;
entry = entry->hash_next;
}
if (entry)
entry->thd= NULL;
DBUG_VOID_RETURN;
}
#ifndef DBUG_OFF
void Active_tranx::assert_thd_is_waiter(THD *thd_to_check,
const char *log_file_name,
my_off_t log_file_pos)
{
DBUG_ENTER("Active_tranx::assert_thd_is_waiter");
mysql_mutex_assert_owner(m_lock);
unsigned int hash_val = get_hash_value(log_file_name, log_file_pos);
Tranx_node *entry = m_trx_htb[hash_val];
while (entry != NULL)
{
if (compare(entry, log_file_name, log_file_pos) == 0)
break;
entry = entry->hash_next;
}
DBUG_ASSERT(entry);
DBUG_ASSERT(entry->thd);
DBUG_ASSERT(entry->thd->thread_id == thd_to_check->thread_id);
DBUG_VOID_RETURN;
}
#endif
/*******************************************************************************
*
* <Repl_semi_sync_master> class: the basic code layer for semisync master.
* <Repl_semi_sync_slave> class: the basic code layer for semisync slave.
*
* The most important functions during semi-syn replication listed:
*
* Master:
* . report_reply_binlog(): called by the binlog dump thread when it receives
* the slave's status information.
* . update_sync_header(): based on transaction waiting information, decide
* whether to request the slave to reply.
* . write_tranx_in_binlog(): called by the transaction thread when it finishes
* writing all transaction events in binlog.
* . commit_trx(): transaction thread wait for the slave reply.
*
* Slave:
* . slave_read_sync_header(): read the semi-sync header from the master, get
* the sync status and get the payload for events.
* . slave_reply(): reply to the master about the replication progress.
*
******************************************************************************/
Repl_semi_sync_master::Repl_semi_sync_master()
: m_active_tranxs(NULL),
m_init_done(false),
m_reply_file_name_inited(false),
m_reply_file_pos(0L),
m_wait_file_name_inited(false),
m_wait_file_pos(0),
m_master_enabled(false),
m_wait_timeout(0L),
m_state(0),
m_wait_point(0)
{
m_reply_file_name[0]= m_wait_file_name[0]= 0;
}
int Repl_semi_sync_master::init_object()
{
int result= 0;
m_init_done = true;
/* References to the parameter works after set_options(). */
set_wait_timeout(rpl_semi_sync_master_timeout);
set_trace_level(rpl_semi_sync_master_trace_level);
set_wait_point(rpl_semi_sync_master_wait_point);
/* Mutex initialization can only be done after MY_INIT(). */
mysql_mutex_init(key_LOCK_rpl_semi_sync_master_enabled,
&LOCK_rpl_semi_sync_master_enabled, MY_MUTEX_INIT_FAST);
mysql_mutex_init(key_LOCK_binlog,
&LOCK_binlog, MY_MUTEX_INIT_FAST);
mysql_cond_init(key_COND_binlog_send,
&COND_binlog_send, NULL);
if (rpl_semi_sync_master_enabled)
{
result = enable_master();
if (!result)
result= ack_receiver.start(); /* Start the ACK thread. */
}
else
disable_master();
return result;
}
int Repl_semi_sync_master::enable_master()
{
int result = 0;
/* Must have the lock when we do enable of disable. */
lock();
if (!get_master_enabled())
{
m_active_tranxs=
new Active_tranx(&LOCK_binlog, &COND_binlog_send, m_trace_level);
if (m_active_tranxs != NULL)
{
m_commit_file_name_inited = false;
m_reply_file_name_inited = false;
m_wait_file_name_inited = false;
set_master_enabled(true);
m_state = true;
sql_print_information("Semi-sync replication enabled on the master.");
}
else
{
sql_print_error("Cannot allocate memory to enable semi-sync on the master.");
result = -1;
}
}
unlock();
return result;
}
void Repl_semi_sync_master::disable_master()
{
/* Must have the lock when we do enable of disable. */
lock();
if (get_master_enabled())
{
/* Switch off the semi-sync first so that waiting transaction will be
* waken up.
*/
switch_off();
DBUG_ASSERT(m_active_tranxs != NULL);
delete m_active_tranxs;
m_active_tranxs = NULL;
m_reply_file_name_inited = false;
m_wait_file_name_inited = false;
m_commit_file_name_inited = false;
set_master_enabled(false);
}
unlock();
}
void Repl_semi_sync_master::cleanup()
{
if (m_init_done)
{
mysql_mutex_destroy(&LOCK_rpl_semi_sync_master_enabled);
mysql_mutex_destroy(&LOCK_binlog);
mysql_cond_destroy(&COND_binlog_send);
m_init_done= 0;
}
delete m_active_tranxs;
}
void Repl_semi_sync_master::create_timeout(struct timespec *out,
struct timespec *start_arg)
{
struct timespec *start_ts;
struct timespec now_ts;
if (!start_arg)
{
set_timespec(now_ts, 0);
start_ts= &now_ts;
}
else
{
start_ts= start_arg;
}
long diff_secs= (long) (m_wait_timeout / TIME_THOUSAND);
long diff_nsecs= (long) ((m_wait_timeout % TIME_THOUSAND) * TIME_MILLION);
long nsecs= start_ts->tv_nsec + diff_nsecs;
out->tv_sec= start_ts->tv_sec + diff_secs + nsecs / TIME_BILLION;
out->tv_nsec= nsecs % TIME_BILLION;
}
void Repl_semi_sync_master::lock()
{
mysql_mutex_lock(&LOCK_binlog);
}
void Repl_semi_sync_master::unlock()
{
mysql_mutex_unlock(&LOCK_binlog);
}
void Repl_semi_sync_master::add_slave()
{
lock();
rpl_semi_sync_master_clients++;
unlock();
}
void Repl_semi_sync_master::remove_slave()
{
lock();
if (!(--rpl_semi_sync_master_clients) && !rpl_semi_sync_master_wait_no_slave)
{
/*
Signal transactions waiting in commit_trx() that they do not have to
wait anymore.
*/
m_active_tranxs->clear_active_tranx_nodes(NULL, 0,
signal_waiting_transaction);
}
unlock();
}
/*
Check report package
@retval 0 ok
@retval 1 Error
@retval -1 Slave is going down (ok)
*/
int Repl_semi_sync_master::report_reply_packet(uint32 server_id,
const uchar *packet,
ulong packet_len)
{
int result= 1; // Assume error
char log_file_name[FN_REFLEN+1];
my_off_t log_file_pos;
ulong log_file_len = 0;
DBUG_ENTER("Repl_semi_sync_master::report_reply_packet");
DBUG_EXECUTE_IF("semisync_corrupt_magic",
const_cast<uchar*>(packet)[REPLY_MAGIC_NUM_OFFSET]= 0;);
if (unlikely(packet[REPLY_MAGIC_NUM_OFFSET] !=
Repl_semi_sync_master::k_packet_magic_num))
{
if (packet[0] == COM_QUIT && packet_len == 1)
{
/* Slave sent COM_QUIT as part of IO thread going down */
sql_print_information("slave IO thread has stopped");
DBUG_RETURN(-1);
}
else
sql_print_error("Read semi-sync reply magic number error");
goto l_end;
}
if (unlikely(packet_len < REPLY_BINLOG_NAME_OFFSET))
{
sql_print_error("Read semi-sync reply length error: packet is too small");
goto l_end;
}
log_file_pos = uint8korr(packet + REPLY_BINLOG_POS_OFFSET);
log_file_len = packet_len - REPLY_BINLOG_NAME_OFFSET;
if (unlikely(log_file_len >= FN_REFLEN))
{
sql_print_error("Read semi-sync reply binlog file length too large");
goto l_end;
}
strncpy(log_file_name, (const char*)packet + REPLY_BINLOG_NAME_OFFSET, log_file_len);
log_file_name[log_file_len] = 0;
DBUG_ASSERT(dirname_length(log_file_name) == 0);
DBUG_PRINT("semisync", ("%s: Got reply(%s, %lu) from server %u",
"Repl_semi_sync_master::report_reply_packet",
log_file_name, (ulong)log_file_pos, server_id));
rpl_semi_sync_master_get_ack++;
report_reply_binlog(server_id, log_file_name, log_file_pos);
DBUG_RETURN(0);
l_end:
{
char buf[256];
octet2hex(buf, (const char*) packet,
MY_MIN(sizeof(buf)-1, (size_t) packet_len));
sql_print_information("First bytes of the packet from semisync slave "
"server-id %d: %s", server_id, buf);
}
DBUG_RETURN(result);
}
int Repl_semi_sync_master::report_reply_binlog(uint32 server_id,
const char *log_file_name,
my_off_t log_file_pos)
{
int cmp;
bool need_copy_send_pos = true;
DBUG_ENTER("Repl_semi_sync_master::report_reply_binlog");
if (!(get_master_enabled()))
DBUG_RETURN(0);
lock();
/* This is the real check inside the mutex. */
if (!get_master_enabled())
goto l_end;
if (!is_on())
/* We check to see whether we can switch semi-sync ON. */
try_switch_on(server_id, log_file_name, log_file_pos);
/* The position should increase monotonically, if there is only one
* thread sending the binlog to the slave.
* In reality, to improve the transaction availability, we allow multiple
* sync replication slaves. So, if any one of them get the transaction,
* the transaction session in the primary can move forward.
*/
if (m_reply_file_name_inited)
{
cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_reply_file_name, m_reply_file_pos);
/* If the requested position is behind the sending binlog position,
* would not adjust sending binlog position.
* We based on the assumption that there are multiple semi-sync slave,
* and at least one of them shou/ld be up to date.
* If all semi-sync slaves are behind, at least initially, the primary
* can find the situation after the waiting timeout. After that, some
* slaves should catch up quickly.
*/
if (cmp < 0)
{
/* If the position is behind, do not copy it. */
need_copy_send_pos = false;
}
}
if (need_copy_send_pos)
{
strmake_buf(m_reply_file_name, log_file_name);
m_reply_file_pos = log_file_pos;
m_reply_file_name_inited = true;
/* Remove all active transaction nodes before this point. */
DBUG_ASSERT(m_active_tranxs != NULL);
m_active_tranxs->clear_active_tranx_nodes(log_file_name, log_file_pos,
signal_waiting_transaction);
if (m_active_tranxs->is_empty())
m_wait_file_name_inited= false;
DBUG_PRINT("semisync", ("%s: Got reply at (%s, %lu)",
"Repl_semi_sync_master::report_reply_binlog",
log_file_name, (ulong)log_file_pos));
}
l_end:
unlock();
DBUG_RETURN(0);
}
int Repl_semi_sync_master::wait_after_sync(const char *log_file,
my_off_t log_pos)
{
if (!get_master_enabled())
return 0;
int ret= 0;
if(log_pos &&
wait_point() == SEMI_SYNC_MASTER_WAIT_POINT_AFTER_BINLOG_SYNC)
ret= commit_trx(log_file + dirname_length(log_file), log_pos);
return ret;
}
int Repl_semi_sync_master::wait_after_commit(THD* thd, bool all)
{
if (!get_master_enabled())
return 0;
int ret= 0;
const char *log_file;
my_off_t log_pos;
bool is_real_trans=
(all || thd->transaction->all.ha_list == 0);
/*
The coordinates are propagated to this point having been computed
in report_binlog_update
*/
Trans_binlog_info *log_info= thd->semisync_info;
log_file= log_info && log_info->log_file[0] ? log_info->log_file : 0;
log_pos= log_info ? log_info->log_pos : 0;
DBUG_ASSERT(!log_file || dirname_length(log_file) == 0);
if (is_real_trans &&
log_pos &&
wait_point() == SEMI_SYNC_MASTER_WAIT_POINT_AFTER_STORAGE_COMMIT)
ret= commit_trx(log_file, log_pos);
if (is_real_trans && log_info)
{
log_info->log_file[0]= 0;
log_info->log_pos= 0;
}
return ret;
}
int Repl_semi_sync_master::wait_after_rollback(THD *thd, bool all)
{
return wait_after_commit(thd, all);
}
/**
The method runs after flush to binary log is done.
*/
int Repl_semi_sync_master::report_binlog_update(THD *trans_thd,
THD *waiter_thd,
const char *log_file,
my_off_t log_pos)
{
if (get_master_enabled())
{
Trans_binlog_info *log_info;
if (!(log_info= trans_thd->semisync_info))
{
if(!(log_info= (Trans_binlog_info*)my_malloc(PSI_INSTRUMENT_ME,
sizeof(Trans_binlog_info), MYF(0))))
return 1;
trans_thd->semisync_info= log_info;
}
strcpy(log_info->log_file, log_file + dirname_length(log_file));
log_info->log_pos = log_pos;
return write_tranx_in_binlog(waiter_thd, log_info->log_file,
log_pos);
}
return 0;
}
int Repl_semi_sync_master::dump_start(THD* thd,
const char *log_file,
my_off_t log_pos)
{
if (!thd->semi_sync_slave)
return 0;
if (ack_receiver.add_slave(thd))
{
sql_print_error("Failed to register slave to semi-sync ACK receiver "
"thread. Turning off semisync");
thd->semi_sync_slave= 0;
return 1;
}
add_slave();
report_reply_binlog(thd->variables.server_id,
log_file + dirname_length(log_file), log_pos);
sql_print_information("Start semi-sync binlog_dump to slave "
"(server_id: %ld), pos(%s, %lu)",
(long) thd->variables.server_id, log_file,
(ulong) log_pos);
/* Mark that semi-sync net->pkt_nr is not reliable */
thd->net.pkt_nr_can_be_reset= 1;
return 0;
}
void Repl_semi_sync_master::dump_end(THD* thd)
{
if (!thd->semi_sync_slave)
return;
sql_print_information("Stop semi-sync binlog_dump to slave (server_id: %ld)",
(long) thd->variables.server_id);
remove_slave();
ack_receiver.remove_slave(thd);
}
int Repl_semi_sync_master::commit_trx(const char *trx_wait_binlog_name,
my_off_t trx_wait_binlog_pos)
{
bool success= 0;
DBUG_ENTER("Repl_semi_sync_master::commit_trx");
if (!rpl_semi_sync_master_clients && !rpl_semi_sync_master_wait_no_slave)
{
rpl_semi_sync_master_no_transactions++;
DBUG_RETURN(0);
}
if (get_master_enabled() && trx_wait_binlog_name)
{
struct timespec start_ts;
struct timespec abstime;
int wait_result;
PSI_stage_info old_stage;
THD *thd= current_thd;
bool aborted __attribute__((unused)) = 0;
set_timespec(start_ts, 0);
DEBUG_SYNC(thd, "rpl_semisync_master_commit_trx_before_lock");
/* Acquire the mutex. */
lock();
/* This must be called after acquired the lock */
THD_ENTER_COND(thd, &thd->COND_wakeup_ready, &LOCK_binlog,
&stage_waiting_for_semi_sync_ack_from_slave, &old_stage);
/* This is the real check inside the mutex. */
if (!get_master_enabled() || !is_on())
goto l_end;
DBUG_PRINT("semisync", ("%s: wait pos (%s, %lu), repl(%d)",
"Repl_semi_sync_master::commit_trx",
trx_wait_binlog_name, (ulong)trx_wait_binlog_pos,
(int)is_on()));
while (is_on() && !(aborted= thd_killed(thd)))
{
/* We have to check these again as things may have changed */
if (!rpl_semi_sync_master_clients && !rpl_semi_sync_master_wait_no_slave)
{
aborted= 1;
break;
}
if (m_reply_file_name_inited)
{
int cmp = Active_tranx::compare(m_reply_file_name, m_reply_file_pos,
trx_wait_binlog_name,
trx_wait_binlog_pos);
if (cmp >= 0)
{
/* We have already sent the relevant binlog to the slave: no need to
* wait here.
*/
DBUG_PRINT("semisync", ("%s: Binlog reply is ahead (%s, %lu),",
"Repl_semi_sync_master::commit_trx",
m_reply_file_name,
(ulong)m_reply_file_pos));
success= 1;
break;
}
}
/* Let us update the info about the minimum binlog position of waiting
* threads.
*/
if (m_wait_file_name_inited)
{
int cmp = Active_tranx::compare(trx_wait_binlog_name,
trx_wait_binlog_pos,
m_wait_file_name, m_wait_file_pos);
if (cmp <= 0)
{
/* This thd has a lower position, let's update the minimum info. */
strmake_buf(m_wait_file_name, trx_wait_binlog_name);
m_wait_file_pos = trx_wait_binlog_pos;
rpl_semi_sync_master_wait_pos_backtraverse++;
DBUG_PRINT("semisync", ("%s: move back wait position (%s, %lu),",
"Repl_semi_sync_master::commit_trx",
m_wait_file_name, (ulong)m_wait_file_pos));
}
}
else
{
strmake_buf(m_wait_file_name, trx_wait_binlog_name);
m_wait_file_pos = trx_wait_binlog_pos;
m_wait_file_name_inited = true;
DBUG_PRINT("semisync", ("%s: init wait position (%s, %lu),",
"Repl_semi_sync_master::commit_trx",
m_wait_file_name, (ulong)m_wait_file_pos));
}
/* In semi-synchronous replication, we wait until the binlog-dump
* thread has received the reply on the relevant binlog segment from the
* replication slave.
*
* Let us suspend this thread to wait on the condition;
* when replication has progressed far enough, we will release
* these waiting threads.
*/
rpl_semi_sync_master_wait_sessions++;
DBUG_PRINT("semisync", ("%s: wait %lu ms for binlog sent (%s, %lu)",
"Repl_semi_sync_master::commit_trx",
m_wait_timeout,
m_wait_file_name, (ulong)m_wait_file_pos));
#ifndef DBUG_OFF
m_active_tranxs->assert_thd_is_waiter(thd, trx_wait_binlog_name,
trx_wait_binlog_pos);
#endif
create_timeout(&abstime, &start_ts);
wait_result= mysql_cond_timedwait(&thd->COND_wakeup_ready, &LOCK_binlog,
&abstime);
rpl_semi_sync_master_wait_sessions--;
if (wait_result != 0)
{
/* This is a real wait timeout. */
sql_print_warning("Timeout waiting for reply of binlog (file: %s, pos: %lu), "
"semi-sync up to file %s, position %lu.",
trx_wait_binlog_name, (ulong)trx_wait_binlog_pos,
m_reply_file_name, (ulong)m_reply_file_pos);
rpl_semi_sync_master_wait_timeouts++;
/* switch semi-sync off */
switch_off();
}
else
{
int wait_time;
wait_time = get_wait_time(start_ts);
if (wait_time < 0)
{
DBUG_PRINT("semisync", ("Replication semi-sync getWaitTime fail at "
"wait position (%s, %lu)",
trx_wait_binlog_name,
(ulong)trx_wait_binlog_pos));
rpl_semi_sync_master_timefunc_fails++;
}
else
{
rpl_semi_sync_master_trx_wait_num++;
rpl_semi_sync_master_trx_wait_time += wait_time;
DBUG_EXECUTE_IF("testing_cond_var_per_thd", {
/*
DBUG log warning to ensure we have either recieved our ACK; or
have timed out and are awoken in an off state. Test
rpl.rpl_semi_sync_cond_var_per_thd scans the logs to ensure this
warning is not present.
*/
bool valid_wakeup=
(!get_master_enabled() || !is_on() || thd->is_killed() ||
0 <= Active_tranx::compare(
m_reply_file_name, m_reply_file_pos,
trx_wait_binlog_name, trx_wait_binlog_pos));
if (!valid_wakeup)
{
sql_print_warning(
"Thread awaiting semi-sync ACK was awoken before its "
"ACK. THD (%llu), Wait coord: (%s, %llu), ACK coord: (%s, "
"%llu)",
thd->thread_id, trx_wait_binlog_name, trx_wait_binlog_pos,
m_reply_file_name, m_reply_file_pos);
}
});
}
}
}
/*
If our THD was killed (rather than awoken from an ACK) notify the
Active_tranx cache that we are no longer waiting for the ACK, so nobody
signals our COND var invalidly.
*/
if (aborted)
m_active_tranxs->unlink_thd_as_waiter(trx_wait_binlog_name,
trx_wait_binlog_pos);
/*
At this point, the binlog file and position of this transaction
must have been removed from Active_tranx.
m_active_tranxs may be NULL if someone disabled semi sync during
mysql_cond_timedwait
*/
DBUG_ASSERT(aborted || !m_active_tranxs || m_active_tranxs->is_empty() ||
!m_active_tranxs->is_tranx_end_pos(trx_wait_binlog_name,
trx_wait_binlog_pos));
l_end:
/* Update the status counter. */
if (success)
rpl_semi_sync_master_yes_transactions++;
else
rpl_semi_sync_master_no_transactions++;
/* The lock held will be released by thd_exit_cond, so no need to
call unlock() here */
THD_EXIT_COND(thd, &old_stage);
}
DBUG_RETURN(0);
}
/* Indicate that semi-sync replication is OFF now.
*
* What should we do when it is disabled? The problem is that we want
* the semi-sync replication enabled again when the slave catches up
* later. But, it is not that easy to detect that the slave has caught
* up. This is caused by the fact that MySQL's replication protocol is
* asynchronous, meaning that if the master does not use the semi-sync
* protocol, the slave would not send anything to the master.
* Still, if the master is sending (N+1)-th event, we assume that it is
* an indicator that the slave has received N-th event and earlier ones.
*
* If semi-sync is disabled, all transactions still update the wait
* position with the last position in binlog. But no transactions will
* wait for confirmations and the active transaction list would not be
* maintained. In binlog dump thread, update_sync_header() checks whether
* the current sending event catches up with last wait position. If it
* does match, semi-sync will be switched on again.
*/
void Repl_semi_sync_master::switch_off()
{
DBUG_ENTER("Repl_semi_sync_master::switch_off");
/* Clear the active transaction list. */
if (m_active_tranxs)
m_active_tranxs->clear_active_tranx_nodes(NULL, 0,
signal_waiting_transaction);
if (m_state)
{
m_state = false;
rpl_semi_sync_master_off_times++;
m_wait_file_name_inited = false;
m_reply_file_name_inited = false;
sql_print_information("Semi-sync replication switched OFF.");
}
DBUG_VOID_RETURN;
}
int Repl_semi_sync_master::try_switch_on(int server_id,
const char *log_file_name,
my_off_t log_file_pos)
{
bool semi_sync_on = false;
DBUG_ENTER("Repl_semi_sync_master::try_switch_on");
/* If the current sending event's position is larger than or equal to the
* 'largest' commit transaction binlog position, the slave is already
* catching up now and we can switch semi-sync on here.
* If m_commit_file_name_inited indicates there are no recent transactions,
* we can enable semi-sync immediately.
*/
if (m_commit_file_name_inited)
{
int cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_commit_file_name, m_commit_file_pos);
semi_sync_on = (cmp >= 0);
}
else
{
semi_sync_on = true;
}
if (semi_sync_on)
{
/* Switch semi-sync replication on. */
m_state = true;
sql_print_information("Semi-sync replication switched ON with slave (server_id: %d) "
"at (%s, %lu)",
server_id, log_file_name,
(ulong)log_file_pos);
}
DBUG_RETURN(0);
}
int Repl_semi_sync_master::reserve_sync_header(String* packet)
{
DBUG_ENTER("Repl_semi_sync_master::reserve_sync_header");
/*
Set the magic number and the sync status. By default, no sync
is required.
*/
packet->append(reinterpret_cast<const char*>(k_sync_header),
sizeof(k_sync_header));
DBUG_RETURN(0);
}
int Repl_semi_sync_master::update_sync_header(THD* thd, unsigned char *packet,
const char *log_file_name,
my_off_t log_file_pos,
bool* need_sync)
{
int cmp = 0;
bool sync = false;
DBUG_ENTER("Repl_semi_sync_master::update_sync_header");
/* If the semi-sync master is not enabled, or the slave is not a semi-sync
* target, do not request replies from the slave.
*/
if (!get_master_enabled() || !thd->semi_sync_slave)
{
*need_sync = false;
DBUG_RETURN(0);
}
lock();
/* This is the real check inside the mutex. */
if (!get_master_enabled())
goto l_end;
if (is_on())
{
/* semi-sync is ON */
if (m_reply_file_name_inited)
{
cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_reply_file_name, m_reply_file_pos);
if (cmp <= 0)
{
/* If we have already got the reply for the event, then we do
* not need to sync the transaction again.
*/
goto l_end;
}
}
cmp = 1;
if (m_wait_file_name_inited)
cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_wait_file_name, m_wait_file_pos);
/* If we are already waiting for some transaction replies which
* are later in binlog, do not wait for this one event.
*/
if (cmp >= 0)
{
/*
* We only wait if the event is a transaction's ending event.
*/
DBUG_ASSERT(m_active_tranxs != NULL);
sync = m_active_tranxs->is_tranx_end_pos(log_file_name,
log_file_pos);
}
}
else
{
if (m_commit_file_name_inited)
{
int cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_commit_file_name, m_commit_file_pos);
sync = (cmp >= 0);
}
else
{
sync = true;
}
}
DBUG_PRINT("semisync", ("%s: server(%lu), (%s, %lu) sync(%d), repl(%d)",
"Repl_semi_sync_master::update_sync_header",
thd->variables.server_id, log_file_name,
(ulong)log_file_pos, sync, (int)is_on()));
*need_sync= sync;
l_end:
unlock();
/*
We do not need to clear sync flag in packet because we set it to 0 when we
reserve the packet header.
*/
if (sync)
packet[2]= k_packet_flag_sync;
DBUG_RETURN(0);
}
int Repl_semi_sync_master::write_tranx_in_binlog(THD *thd,
const char *log_file_name,
my_off_t log_file_pos)
{
int result = 0;
DBUG_ENTER("Repl_semi_sync_master::write_tranx_in_binlog");
lock();
/* This is the real check inside the mutex. */
if (!get_master_enabled())
goto l_end;
/* Update the 'largest' transaction commit position seen so far even
* though semi-sync is switched off.
* It is much better that we update m_commit_file* here, instead of
* inside commit_trx(). This is mostly because update_sync_header()
* will watch for m_commit_file* to decide whether to switch semi-sync
* on. The detailed reason is explained in function update_sync_header().
*/
if (m_commit_file_name_inited)
{
int cmp = Active_tranx::compare(log_file_name, log_file_pos,
m_commit_file_name, m_commit_file_pos);
if (cmp > 0)
{
/* This is a larger position, let's update the maximum info. */
strncpy(m_commit_file_name, log_file_name, FN_REFLEN-1);
m_commit_file_name[FN_REFLEN-1] = 0; /* make sure it ends properly */
m_commit_file_pos = log_file_pos;
}
}
else
{
strncpy(m_commit_file_name, log_file_name, FN_REFLEN-1);
m_commit_file_name[FN_REFLEN-1] = 0; /* make sure it ends properly */
m_commit_file_pos = log_file_pos;
m_commit_file_name_inited = true;
}
if (is_on())
{
DBUG_ASSERT(m_active_tranxs != NULL);
if(m_active_tranxs->insert_tranx_node(thd, log_file_name, log_file_pos))
{
/*
if insert tranx_node failed, print a warning message
and turn off semi-sync
*/
sql_print_warning("Semi-sync failed to insert tranx_node for binlog file: %s, position: %lu",
log_file_name, (ulong)log_file_pos);
switch_off();
}
else
{
rpl_semi_sync_master_request_ack++;
}
}
l_end:
unlock();
DBUG_RETURN(result);
}
int Repl_semi_sync_master::flush_net(THD *thd,
const char *event_buf)
{
int result = -1;
NET* net= &thd->net;
DBUG_ENTER("Repl_semi_sync_master::flush_net");
DBUG_ASSERT((unsigned char)event_buf[1] == k_packet_magic_num);
if ((unsigned char)event_buf[2] != k_packet_flag_sync)
{
/* current event does not require reply */
result = 0;
goto l_end;
}
/* We flush to make sure that the current event is sent to the network,
* instead of being buffered in the TCP/IP stack.
*/
if (net_flush(net))
{
sql_print_error("Semi-sync master failed on net_flush() "
"before waiting for slave reply");
goto l_end;
}
/*
We have to do a net_clear() as with semi-sync the slave_reply's are
interleaved with data from the master and then the net->pkt_nr
cannot be kept in sync. Better to start pkt_nr from 0 again.
*/
net_clear(net, 0);
net->pkt_nr++;
net->compress_pkt_nr++;
result = 0;
rpl_semi_sync_master_net_wait_num++;
l_end:
thd->clear_error();
DBUG_RETURN(result);
}
int Repl_semi_sync_master::after_reset_master()
{
int result = 0;
DBUG_ENTER("Repl_semi_sync_master::after_reset_master");
if (rpl_semi_sync_master_enabled)
{
sql_print_information("Enable Semi-sync Master after reset master");
enable_master();
}
lock();
m_state = get_master_enabled() ? 1 : 0;
m_wait_file_name_inited = false;
m_reply_file_name_inited = false;
m_commit_file_name_inited = false;
rpl_semi_sync_master_yes_transactions = 0;
rpl_semi_sync_master_no_transactions = 0;
rpl_semi_sync_master_off_times = 0;
rpl_semi_sync_master_timefunc_fails = 0;
rpl_semi_sync_master_wait_sessions = 0;
rpl_semi_sync_master_wait_pos_backtraverse = 0;
rpl_semi_sync_master_trx_wait_num = 0;
rpl_semi_sync_master_trx_wait_time = 0;
rpl_semi_sync_master_net_wait_num = 0;
rpl_semi_sync_master_net_wait_time = 0;
unlock();
DBUG_RETURN(result);
}
int Repl_semi_sync_master::before_reset_master()
{
int result = 0;
DBUG_ENTER("Repl_semi_sync_master::before_reset_master");
if (rpl_semi_sync_master_enabled)
disable_master();
DBUG_RETURN(result);
}
void Repl_semi_sync_master::set_export_stats()
{
lock();
rpl_semi_sync_master_status = m_state;
rpl_semi_sync_master_avg_trx_wait_time=
((rpl_semi_sync_master_trx_wait_num) ?
(ulong)((double)rpl_semi_sync_master_trx_wait_time /
((double)rpl_semi_sync_master_trx_wait_num)) : 0);
rpl_semi_sync_master_avg_net_wait_time=
((rpl_semi_sync_master_net_wait_num) ?
(ulong)((double)rpl_semi_sync_master_net_wait_time /
((double)rpl_semi_sync_master_net_wait_num)) : 0);
unlock();
}
void Repl_semi_sync_master::await_all_slave_replies(const char *msg)
{
struct timespec timeout;
int wait_result= 0;
bool first= true;
DBUG_ENTER("Repl_semi_sync_master::::await_all_slave_replies");
/*
Wait for all transactions that need ACKS to have received them; or timeout.
If it is a timeout, the connection thread should attempt to turn off
semi-sync and broadcast to all other waiting threads to move on.
COND_binlog_send is only signalled after the Active_tranx cache has been
emptied.
*/
create_timeout(&timeout, NULL);
lock();
while (get_master_enabled() && is_on() && !m_active_tranxs->is_empty() && !wait_result)
{
if (msg && first)
{
first= false;
sql_print_information(msg);
}
wait_result=
mysql_cond_timedwait(&COND_binlog_send, &LOCK_binlog, &timeout);
}
unlock();
DBUG_VOID_RETURN;
}
/* Get the waiting time given the wait's staring time.
*
* Return:
* >= 0: the waiting time in microsecons(us)
* < 0: error in get time or time back traverse
*/
static int get_wait_time(const struct timespec& start_ts)
{
ulonglong start_usecs, end_usecs;
struct timespec end_ts;
/* Starting time in microseconds(us). */
start_usecs = timespec_to_usec(&start_ts);
/* Get the wait time interval. */
set_timespec(end_ts, 0);
/* Ending time in microseconds(us). */
end_usecs = timespec_to_usec(&end_ts);
if (end_usecs < start_usecs)
return -1;
return (int)(end_usecs - start_usecs);
}
void semi_sync_master_deinit()
{
repl_semisync_master.cleanup();
ack_receiver.cleanup();
}
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