MDEV-26450: Corruption due to innodb_undo_log_truncate

At least since commit 055a3334
(MDEV-13564) the undo log truncation in InnoDB did not work correctly.

The main issue is that during the execution of
trx_purge_truncate_history() some pages of the newly truncated
undo tablespace could be discarded.

This is improved from commit 1cb218c3
which was applied to earlier-version branches.

fsp_try_extend_data_file(): Apply the peculiar rounding of
fil_space_t::size_in_header only to the system tablespace,
whose size can be expressed in megabytes in a configuration parameter.
Other files may freely grow by a number of pages.

fseg_alloc_free_page_low(): Do allow the extension of undo tablespaces,
and mention the file name in the error message.

mtr_t::commit_shrink(): Implement crash-safe shrinking of a tablespace:
(1) durably write the log
(2) release the page latches of the rebuilt tablespace
(3) release the mutexes
(4) truncate the file
(5) release the tablespace latch
This is refactored from trx_purge_truncate_history().

log_write_and_flush_prepare(), log_write_and_flush(): New functions
to durably write log during mtr_t::commit_shrink().

mysql-test/suite/innodb/r/undo_truncate.result

@@ -7,28 +7,12 @@ SET @trunc_start=
 WHERE variable_name = 'innodb_undo_truncations');
 create table t1(keyc int primary key, c char(100)) engine = innodb;
 create table t2(keyc int primary key, c char(100)) engine = innodb;
-CREATE PROCEDURE populate_t1()
-BEGIN
-DECLARE i INT DEFAULT 1;
-while (i <= 20000) DO
-insert into t1 values (i, 'a');
-SET i = i + 1;
-END WHILE;
-END |
-CREATE PROCEDURE populate_t2()
-BEGIN
-DECLARE i INT DEFAULT 1;
-while (i <= 20000) DO
-insert into t2 values (i, 'a');
-SET i = i + 1;
-END WHILE;
-END |
 connect  con1,localhost,root,,;
 begin;
-call populate_t1();
+insert into t1 select seq,'a' from seq_1_to_20000;
 connect  con2,localhost,root,,;
 begin;
-call populate_t2();
+insert into t2 select seq,'a' from seq_1_to_20000;
 connection con1;
 update t1 set c = 'mysql';
 connection con2;
@@ -50,8 +34,6 @@ commit;
 disconnect con2;
 connection default;
 drop table t1, t2;
-drop PROCEDURE populate_t1;
-drop PROCEDURE populate_t2;
 InnoDB		0 transactions not purged
 SET GLOBAL innodb_purge_rseg_truncate_frequency = @save_frequency;
 SET GLOBAL innodb_undo_log_truncate = @save_truncate;

mysql-test/suite/innodb/t/undo_truncate.test

 --source include/have_innodb.inc
 --source include/innodb_page_size.inc
 --source include/have_undo_tablespaces.inc
+--source include/have_sequence.inc
 
 SET @save_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
 SET @save_truncate = @@GLOBAL.innodb_undo_log_truncate;
@@ -19,37 +20,14 @@ WHERE variable_name = 'innodb_undo_truncations');
 create table t1(keyc int primary key, c char(100)) engine = innodb;
 create table t2(keyc int primary key, c char(100)) engine = innodb;
 #
-delimiter |;
-CREATE PROCEDURE populate_t1()
-BEGIN
-        DECLARE i INT DEFAULT 1;
-        while (i <= 20000) DO
-                insert into t1 values (i, 'a');
-                SET i = i + 1;
-        END WHILE;
-END |
-delimiter ;|
-#
-delimiter |;
-CREATE PROCEDURE populate_t2()
-BEGIN
-        DECLARE i INT DEFAULT 1;
-        while (i <= 20000) DO
-                insert into t2 values (i, 'a');
-                SET i = i + 1;
-        END WHILE;
-END |
-delimiter ;|
-#
-#
 let DATADIR = `select @@datadir`;
 connect (con1,localhost,root,,);
 begin;
-send call populate_t1();
+send insert into t1 select seq,'a' from seq_1_to_20000;
 
 connect (con2,localhost,root,,);
 begin;
-send call populate_t2();
+send insert into t2 select seq,'a' from seq_1_to_20000;
 
 connection con1; reap; send update t1 set c = 'mysql';
 connection con2; reap; send update t2 set c = 'mysql';
@@ -59,25 +37,12 @@ connection con1; reap; send delete from t1;
 connection con2; reap; delete from t2;
 connection con1; reap;
 
-let CHECKFILE = $MYSQL_TMP_DIR/check.txt;
-perl;
-($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size1)
-	= stat("$ENV{DATADIR}/undo001");
-($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size2)
-	= stat("$ENV{DATADIR}/undo002");
-open(OUT, ">$ENV{CHECKFILE}") || die;
-print OUT "let \$size1='$size1,$size2';\n";
-close(OUT);
-EOF
-
 SET GLOBAL innodb_undo_log_truncate = 1;
 commit; disconnect con1;
 connection con2; commit; disconnect con2;
 
 connection default;
 drop table t1, t2;
-drop PROCEDURE populate_t1;
-drop PROCEDURE populate_t2;
 
 --source include/wait_all_purged.inc
 
@@ -93,28 +58,5 @@ if (`select @@innodb_page_size IN (8192,16384)`)
   source include/wait_condition.inc;
 }
 
---source $CHECKFILE
-perl;
-($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size1)
-	= stat("$ENV{DATADIR}/undo001");
-($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size2)
-	= stat("$ENV{DATADIR}/undo002");
-open(OUT, ">$ENV{CHECKFILE}") || die;
-print OUT "let \$size2='$size1,$size2';\n";
-close(OUT);
-EOF
-
---source $CHECKFILE
---remove_file $CHECKFILE
-
-if ($size1 == $size2)
-{
-  # This fails for innodb_page_size=64k, occasionally also for 32k.
-  if (`select @@innodb_page_size IN (8192,16384)`)
-  {
-    echo Truncation did not happen: $size1;
-  }
-}
-
 SET GLOBAL innodb_purge_rseg_truncate_frequency = @save_frequency;
 SET GLOBAL innodb_undo_log_truncate = @save_truncate;

storage/innobase/fsp/fsp0fsp.cc

@@ -780,10 +780,12 @@ fsp_try_extend_data_file(fil_space_t *space, buf_block_t *header, mtr_t *mtr)
 		return(0);
 	}
 
-	/* We ignore any fragments of a full megabyte when storing the size
-	to the space header */
+	/* For the system tablespace, we ignore any fragments of a
+	full megabyte when storing the size to the space header */
 
-	space->size_in_header = ut_2pow_round(space->size, (1024 * 1024) / ps);
+	space->size_in_header = space->id
+		? space->size
+		: ut_2pow_round(space->size, (1024 * 1024) / ps);
 
 	/* recv_sys_t::parse() expects to find a WRITE record that
 	covers all 4 bytes. Therefore, we must specify mtr_t::FORCED
@@ -2130,14 +2132,14 @@ fseg_alloc_free_page_low(
 		return(NULL);
 	}
 
-	if (space->size <= ret_page && !is_system_tablespace(space_id)) {
+	if (space->size <= ret_page && !is_predefined_tablespace(space_id)) {
 		/* It must be that we are extending a single-table
 		tablespace whose size is still < 64 pages */
 
 		if (ret_page >= FSP_EXTENT_SIZE) {
-			ib::error() << "Error (2): trying to extend"
-			" a single-table tablespace " << space_id
-			<< " by single page(s) though the"
+			ib::error() << "Trying to extend '"
+			<< space->chain.start->name
+			<< "' by single page(s) though the"
 			<< " space size " << space->size
 			<< ". Page no " << ret_page << ".";
 			ut_ad(!has_done_reservation);

storage/innobase/include/log0log.h

@@ -107,12 +107,16 @@ be flushed to the file system
 @param[in]	rotate_key	whether to rotate the encryption key */
 void log_write_up_to(lsn_t lsn, bool flush_to_disk, bool rotate_key = false);
 
-/** write to the log file up to the last log entry.
-@param[in]	sync	whether we want the written log
-also to be flushed to disk. */
-void
-log_buffer_flush_to_disk(
-	bool sync = true);
+/** Write to the log file up to the last log entry.
+@param sync  whether to wait for a durable write to complete */
+void log_buffer_flush_to_disk(bool sync= true);
+
+
+/** Prepare to invoke log_write_and_flush(), before acquiring log_sys.mutex. */
+ATTRIBUTE_COLD void log_write_and_flush_prepare();
+
+/** Durably write the log up to log_sys.lsn() and release log_sys.mutex. */
+ATTRIBUTE_COLD void log_write_and_flush();
 
 /** Make a checkpoint */
 ATTRIBUTE_COLD void log_make_checkpoint();

storage/innobase/include/mtr0mtr.h

@@ -98,6 +98,10 @@ struct mtr_t {
   /** Commit the mini-transaction. */
   void commit();
 
+  /** Commit a mini-transaction that is shrinking a tablespace.
+  @param space   tablespace that is being shrunk */
+  ATTRIBUTE_COLD void commit_shrink(fil_space_t &space);
+
   /** Commit a mini-transaction that did not modify any pages,
   but generated some redo log on a higher level, such as
   FILE_MODIFY records and an optional FILE_CHECKPOINT marker.

storage/innobase/include/mtr0mtr.ic

@@ -48,8 +48,8 @@ mtr_t::memo_push(void* object, mtr_memo_type_t type)
 
 	/* If this mtr has x-fixed a clean page then we set
 	the made_dirty flag. This tells us if we need to
-	grab log_flush_order_mutex at mtr_commit so that we
-	can insert the dirtied page to the flush list. */
+	grab log_sys.flush_order_mutex at mtr_t::commit() so that we
+	can insert the dirtied page into the flush list. */
 
 	if ((type == MTR_MEMO_PAGE_X_FIX || type == MTR_MEMO_PAGE_SX_FIX)
 	    && !m_made_dirty) {

storage/innobase/log/log0log.cc

@@ -835,15 +835,41 @@ void log_write_up_to(lsn_t lsn, bool flush_to_disk, bool rotate_key)
   log_flush_notify(flush_lsn);
 }
 
-/** write to the log file up to the last log entry.
-@param[in]	sync	whether we want the written log
-also to be flushed to disk. */
+/** Write to the log file up to the last log entry.
+@param sync  whether to wait for a durable write to complete */
 void log_buffer_flush_to_disk(bool sync)
 {
   ut_ad(!srv_read_only_mode);
   log_write_up_to(log_sys.get_lsn(std::memory_order_acquire), sync);
 }
 
+/** Prepare to invoke log_write_and_flush(), before acquiring log_sys.mutex. */
+ATTRIBUTE_COLD void log_write_and_flush_prepare()
+{
+  mysql_mutex_assert_not_owner(&log_sys.mutex);
+
+  while (flush_lock.acquire(log_sys.get_lsn() + 1) !=
+         group_commit_lock::ACQUIRED);
+  while (write_lock.acquire(log_sys.get_lsn() + 1) !=
+         group_commit_lock::ACQUIRED);
+}
+
+/** Durably write the log and release log_sys.mutex */
+ATTRIBUTE_COLD void log_write_and_flush()
+{
+  ut_ad(!srv_read_only_mode);
+  auto lsn= log_sys.get_lsn();
+  write_lock.set_pending(lsn);
+  log_write(false);
+  ut_a(log_sys.write_lsn == lsn);
+  write_lock.release(lsn);
+
+  lsn= write_lock.value();
+  flush_lock.set_pending(lsn);
+  log_write_flush_to_disk_low(lsn);
+  flush_lock.release(lsn);
+}
+
 /********************************************************************
 
 Tries to establish a big enough margin of free space in the log buffer, such

storage/innobase/mtr/mtr0mtr.cc

 /*****************************************************************************
 
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2020, MariaDB Corporation.
+Copyright (c) 2017, 2021, MariaDB Corporation.
 
 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
@@ -459,6 +459,115 @@ void mtr_t::commit()
   release_resources();
 }
 
+#ifdef UNIV_DEBUG
+/** Check that all pages belong to a shrunk tablespace. */
+struct Shrink
+{
+  const page_id_t low, high;
+  Shrink(const fil_space_t &space) :
+    low({space.id, 0}), high({space.id, space.size}) {}
+
+  bool operator()(const mtr_memo_slot_t *slot) const
+  {
+    if (!slot->object)
+      return true;
+    switch (slot->type) {
+    default:
+      ut_ad("invalid type" == 0);
+      return false;
+    case MTR_MEMO_SPACE_X_LOCK:
+      ut_ad(low.space() == static_cast<fil_space_t*>(slot->object)->id);
+      return true;
+    case MTR_MEMO_PAGE_X_MODIFY:
+    case MTR_MEMO_PAGE_SX_MODIFY:
+    case MTR_MEMO_PAGE_X_FIX:
+    case MTR_MEMO_PAGE_SX_FIX:
+      const auto &bpage= static_cast<buf_block_t*>(slot->object)->page;
+      const auto id= bpage.id();
+      if (id == page_id_t{0, TRX_SYS_PAGE_NO})
+      {
+        ut_ad(srv_is_undo_tablespace(low.space()));
+        break;
+      }
+      ut_ad(id >= low);
+      ut_ad(id < high);
+      ut_ad(bpage.state() == BUF_BLOCK_FILE_PAGE);
+      ut_ad(bpage.oldest_modification() <= 1);
+      break;
+    }
+    return true;
+  }
+};
+#endif
+
+/** Commit a mini-transaction that is shrinking a tablespace.
+@param space   tablespace that is being shrunk */
+void mtr_t::commit_shrink(fil_space_t &space)
+{
+  ut_ad(is_active());
+  ut_ad(!is_inside_ibuf());
+  ut_ad(!high_level_read_only);
+  ut_ad(m_modifications);
+  ut_ad(m_made_dirty);
+  ut_ad(!recv_recovery_is_on());
+  ut_ad(m_log_mode == MTR_LOG_ALL);
+  ut_ad(UT_LIST_GET_LEN(space.chain) == 1);
+
+  log_write_and_flush_prepare();
+
+  const lsn_t start_lsn= finish_write(prepare_write()).first;
+
+  mysql_mutex_lock(&log_sys.flush_order_mutex);
+  /* Durably write the reduced FSP_SIZE before truncating the data file. */
+  log_write_and_flush();
+
+  if (m_freed_pages)
+  {
+    ut_ad(!m_freed_pages->empty());
+    ut_ad(m_freed_space == &space);
+    ut_ad(memo_contains(*m_freed_space));
+    ut_ad(is_named_space(m_freed_space));
+    m_freed_space->update_last_freed_lsn(m_commit_lsn);
+
+    if (!is_trim_pages())
+      for (const auto &range : *m_freed_pages)
+        m_freed_space->add_free_range(range);
+    else
+      m_freed_space->clear_freed_ranges();
+    delete m_freed_pages;
+    m_freed_pages= nullptr;
+    m_freed_space= nullptr;
+    /* mtr_t::start() will reset m_trim_pages */
+  }
+  else
+    ut_ad(!m_freed_space);
+
+  ut_d(m_memo.for_each_block_in_reverse(CIterate<Shrink>{space}));
+
+  m_memo.for_each_block_in_reverse(CIterate<const ReleaseBlocks>
+                                   (ReleaseBlocks(start_lsn, m_commit_lsn,
+                                                  m_memo)));
+  mysql_mutex_unlock(&log_sys.flush_order_mutex);
+
+  mutex_enter(&fil_system.mutex);
+  ut_ad(space.is_being_truncated);
+  ut_ad(space.is_stopping());
+  space.set_stopping(false);
+  space.is_being_truncated= false;
+  mutex_exit(&fil_system.mutex);
+
+  /* Truncate the file before releasing the space.latch. File extension
+  (and any allocation of pages beyond the current intended end of the file)
+  is covered by exclusive space.latch, which we are still holding here. */
+  os_file_truncate(space.chain.start->name, space.chain.start->handle,
+                   os_offset_t{space.size} << srv_page_size_shift, true);
+
+  m_memo.for_each_block_in_reverse(CIterate<ReleaseLatches>());
+  srv_stats.log_write_requests.inc();
+
+  release_resources();
+}
+
 /** Commit a mini-transaction that did not modify any pages,
 but generated some redo log on a higher level, such as
 FILE_MODIFY records and an optional FILE_CHECKPOINT marker.

storage/innobase/trx/trx0purge.cc

@@ -754,27 +754,11 @@ static void trx_purge_truncate_history()
 			rseg->needs_purge = false;
 		}
 
-		mtr.commit();
-		/* Write-ahead the redo log record. */
-		log_write_up_to(mtr.commit_lsn(), true);
-
-		/* Trim the file size. */
-		os_file_truncate(file->name, file->handle,
-				 os_offset_t(size) << srv_page_size_shift,
-				 true);
+		mtr.commit_shrink(space);
 
-		/* This is only executed by srv_purge_coordinator_thread. */
+		/* No mutex; this is only updated by the purge coordinator. */
 		export_vars.innodb_undo_truncations++;
 
-		/* In MDEV-8319 (10.5) we will PUNCH_HOLE the garbage
-		(with write-ahead logging). */
-		mutex_enter(&fil_system.mutex);
-		ut_ad(&space == purge_sys.truncate.current);
-		ut_ad(space.is_being_truncated);
-		purge_sys.truncate.current->set_stopping(false);
-		purge_sys.truncate.current->is_being_truncated = false;
-		mutex_exit(&fil_system.mutex);
-
 		if (purge_sys.rseg != NULL
 		    && purge_sys.rseg->last_page_no == FIL_NULL) {
 			/* If purge_sys.rseg is pointing to rseg that
@@ -806,6 +790,7 @@ static void trx_purge_truncate_history()
 
 		ib::info() << "Truncated " << file->name;
 		purge_sys.truncate.last = purge_sys.truncate.current;
+		ut_ad(&space == purge_sys.truncate.current);
 		purge_sys.truncate.current = NULL;
 	}
 }