MDEV-26445 innodb_undo_log_truncate is unnecessarily slow

trx_purge_truncate_history(): Do not force a write of the undo tablespace
that is being truncated. Instead, prevent page writes by acquiring
an exclusive latch on all dirty pages of the tablespace.

fseg_create(): Relax an assertion that could fail if a dirty undo page
is being initialized during undo tablespace truncation (and
trx_purge_truncate_history() already acquired an exclusive latch on it).

fsp_page_create(): If we are truncating a tablespace, try to reuse
a page that we may have already latched exclusively (because it was
in buf_pool.flush_list). To some extent, this helps the test
innodb.undo_truncate,16k to avoid running out of buffer pool.

mtr_t::commit_shrink(): Mark as clean all pages that are outside the
new bounds of the tablespace, and only add the newly reinitialized pages
to the buf_pool.flush_list.

buf_page_create(): Do not unnecessarily invoke change buffer merge on
undo tablespaces.

buf_page_t::clear_oldest_modification(bool temporary): Move some
assertions to the caller buf_page_write_complete().

innodb.undo_truncate: Use a bigger innodb_buffer_pool_size=24M.
On my system, it would otherwise hang 1 out of 1547 attempts
(on the 40th repeat of innodb.undo_truncate,16k).
Other page sizes were not affected.

2 files changed, 3 insertions, 0 deletions

diff --git a/storage/innobase/buf/buf0buf.cc b/storage/innobase/buf/buf0buf.cc
index 113da7746fa..1c126191df3 100644
--- a/storage/innobase/buf/buf0buf.cc
+++ b/storage/innobase/buf/buf0buf.cc
@@ -3796,6 +3796,7 @@ loop:
   /* Delete possible entries for the page from the insert buffer:
   such can exist if the page belonged to an index which was dropped */
   if (page_id < page_id_t{SRV_SPACE_ID_UPPER_BOUND, 0} &&
+      !srv_is_undo_tablespace(page_id.space()) &&
       !recv_recovery_is_on())
     ibuf_merge_or_delete_for_page(nullptr, page_id, zip_size);
 
diff --git a/storage/innobase/buf/buf0flu.cc b/storage/innobase/buf/buf0flu.cc
index eada6bde282..7bf26515e88 100644
--- a/storage/innobase/buf/buf0flu.cc
+++ b/storage/innobase/buf/buf0flu.cc
@@ -363,10 +363,12 @@ void buf_page_write_complete(const IORequest &request)
   const bool temp= fsp_is_system_temporary(bpage->id().space());
 
   mysql_mutex_lock(&buf_pool.mutex);
+  mysql_mutex_assert_not_owner(&buf_pool.flush_list_mutex);
   buf_pool.stat.n_pages_written++;
   /* While we do not need any mutex for clearing oldest_modification
   here, we hope that it will be in the same cache line with io_fix,
   whose changes must be protected by buf_pool.mutex. */
+  ut_ad(temp || bpage->oldest_modification() > 2);
   bpage->clear_oldest_modification(temp);
   ut_ad(bpage->io_fix() == BUF_IO_WRITE);
   bpage->set_io_fix(BUF_IO_NONE);