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MDEV-38069 Heavy contention on buf_pool.flush_list_mutex

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buf_do_flush_list_batch(): Release and reacquire buf_pool.flush_list_mutex
after every 32 iterations, similar to how buf_flush_LRU_list_batch()
releases buf_pool.mutex ever since
commit 27ff972be2 (MDEV-26827 fixup).

This regression was introduced in
commit 22b62edaed (MDEV-25113)
and made more prominent by the recent
commit a7f0d79f8c (MDEV-35155).

Reviewed by: Thirunarayanan Balathandayuthapani
Tested by: Saahil Alam
Tested by: Rahul Raj
This commit is contained in:
Marko Mäkelä 2025-11-17 14:52:10 +02:00
commit 4c94cd5da6
1 changed files with 50 additions and 38 deletions
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92
storage/innobase/buf/buf0flu.cc
View file

@ -1463,7 +1463,16 @@ static ulint buf_do_flush_list_batch(ulint max_n, lsn_t lsn) noexcept
buf_pool.delete_from_flush_list(bpage);
skip:
bpage= prev;
continue;
if (scanned & 31)
continue;
/* Release the buf_pool.flush_list_mutex every now and then
in order to reduce the wait time in buf_flush_ahead().
We attempt to preserve the pointer position while yielding.
Any thread that would remove 'prev' from buf_pool.flush_list
must adjust the hazard pointer. */
buf_pool.flush_hp.set(prev);
mysql_mutex_unlock(&buf_pool.flush_list_mutex);
goto next;
}
ut_ad(oldest_modification > 2);
@ -1491,51 +1500,54 @@ static ulint buf_do_flush_list_batch(ulint max_n, lsn_t lsn) noexcept
buf_pool.flush_hp.set(prev);
}
const page_id_t page_id(bpage->id());
const uint32_t space_id= page_id.space();
if (!space || space->id != space_id)
{
if (last_space_id != space_id)
const page_id_t page_id(bpage->id());
const uint32_t space_id= page_id.space();
if (!space || space->id != space_id)
{
if (last_space_id != space_id)
{
mysql_mutex_unlock(&buf_pool.flush_list_mutex);
mysql_mutex_unlock(&buf_pool.mutex);
if (space)
space->release();
auto p= buf_flush_space(space_id);
space= p.first;
last_space_id= space_id;
mysql_mutex_lock(&buf_pool.mutex);
buf_pool.stat.n_pages_written+= p.second;
mysql_mutex_lock(&buf_pool.flush_list_mutex);
}
else
ut_ad(!space);
}
else if (space->is_stopping_writes())
{
space->release();
space= nullptr;
}
if (!space)
buf_flush_discard_page(bpage);
else
{
mysql_mutex_unlock(&buf_pool.flush_list_mutex);
mysql_mutex_unlock(&buf_pool.mutex);
if (space)
space->release();
auto p= buf_flush_space(space_id);
space= p.first;
last_space_id= space_id;
mysql_mutex_lock(&buf_pool.mutex);
buf_pool.stat.n_pages_written+= p.second;
mysql_mutex_lock(&buf_pool.flush_list_mutex);
do
{
if (neighbors && space->is_rotational())
count+= buf_flush_try_neighbors(space, page_id, bpage,
neighbors == 1, count, max_n);
else if (bpage->flush(space))
++count;
else
continue;
mysql_mutex_lock(&buf_pool.mutex);
}
while (0);
}
else
ut_ad(!space);
}
else if (space->is_stopping_writes())
{
space->release();
space= nullptr;
}
if (!space)
buf_flush_discard_page(bpage);
else
{
mysql_mutex_unlock(&buf_pool.flush_list_mutex);
do
{
if (neighbors && space->is_rotational())
count+= buf_flush_try_neighbors(space, page_id, bpage,
neighbors == 1, count, max_n);
else if (bpage->flush(space))
++count;
else
continue;
mysql_mutex_lock(&buf_pool.mutex);
}
while (0);
}
next:
mysql_mutex_lock(&buf_pool.flush_list_mutex);
bpage= buf_pool.flush_hp.get();
}