Bug #30197056 INNODB: ASSERTION FAILURE: PAGE_TYPE == FIL_PAGE_TYPE_ZLOB_FIRST AT ZLOB0READ.CC

Problem:

Consider the scenario where the zlob (compressed LOB) is stored in old format using
a single zlib stream.  The purge will process this zlob by removing the first page of
the LOB repeatedly.  There seems to be a race condition b/w purge thread and an update
thread that is reusing a delete marked record.  Because of this the update thread
sees a lob whose first page is of type FIL_PAGE_TYPE_ZBLOB2, which suggests that
the zlob is partially purged.

The test case just demonstrates that it is possible for the first page of LOB
to be FIL_PAGE_TYPE_ZBLOB2 because of partial purging.

Solution:

I think we can remove the failing assert.

rb#23293 approved by Kuba <[email protected]>

Author: gurusami

mysql-test/suite/innodb/r/zlob_rollback_crash_6.result

@@ -0,0 +1,19 @@
+#
+# Bug #30197056 INNODB: ASSERTION FAILURE: PAGE_TYPE ==
+# FIL_PAGE_TYPE_ZLOB_FIRST AT ZLOB0READ.CC
+#
+SET GLOBAL innodb_compression_level = 0;
+CREATE TABLE t1 (f1 INT PRIMARY KEY, f2 LONGBLOB) ROW_FORMAT=COMPRESSED;
+INSERT INTO t1 VALUES (1, REPEAT('+', 40000));
+SET DEBUG = '+d,lob_insert_single_zstream';
+START TRANSACTION;
+INSERT INTO t1 VALUES (2, REPEAT('~', 40000));
+SET DEBUG = '+d,ib_zlob_deleter_middle_crash';
+ROLLBACK;
+ERROR HY000: Lost connection to MySQL server during query
+# restart
+SELECT f1, LENGTH(f2) FROM t1 FOR UPDATE;
+f1	LENGTH(f2)
+1	40000
+DROP TABLE t1;
+SET GLOBAL innodb_compression_level = DEFAULT;

mysql-test/suite/innodb/t/zlob_rollback_crash_6.test

@@ -0,0 +1,34 @@
+--source include/have_debug.inc
+--source include/have_innodb_max_16k.inc
+
+--echo #
+--echo # Bug #30197056 INNODB: ASSERTION FAILURE: PAGE_TYPE ==
+--echo # FIL_PAGE_TYPE_ZLOB_FIRST AT ZLOB0READ.CC
+--echo #
+
+SET GLOBAL innodb_compression_level = 0;
+
+CREATE TABLE t1 (f1 INT PRIMARY KEY, f2 LONGBLOB) ROW_FORMAT=COMPRESSED;
+
+# The size of the BLOB is specified as 40000 bytes so that it will be
+# stored externally.
+INSERT INTO t1 VALUES (1, REPEAT('+', 40000));
+
+SET DEBUG = '+d,lob_insert_single_zstream';
+
+START TRANSACTION;
+INSERT INTO t1 VALUES (2, REPEAT('~', 40000));
+
+--source include/expect_crash.inc
+
+SET DEBUG = '+d,ib_zlob_deleter_middle_crash';
+--error 2013
+ROLLBACK;
+
+--source include/start_mysqld.inc
+
+SELECT f1, LENGTH(f2) FROM t1 FOR UPDATE;
+DROP TABLE t1;
+
+SET GLOBAL innodb_compression_level = DEFAULT;
+

storage/innobase/include/mtr0mtr.h

@@ -430,6 +430,7 @@ struct mtr_t {
     return (m_impl.m_log.size() + (m_impl.m_n_log_recs > 1 ? 1 : 0));
   }
 
+  void wait_for_flush();
 #endif /* UNIV_DEBUG */
 
   /** @return true if a record was added to the mini-transaction */

storage/innobase/lob/lob0del.cc

@@ -1,6 +1,6 @@
 /*****************************************************************************
 
-Copyright (c) 2015, 2018, Oracle and/or its affiliates. All Rights Reserved.
+Copyright (c) 2015, 2019, Oracle and/or its affiliates. All Rights Reserved.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License, version 2.0, as published by the
@@ -120,6 +120,11 @@ dberr_t Deleter::destroy() {
     if (err != DB_SUCCESS) {
       break;
     }
+
+    DBUG_EXECUTE_IF("ib_zlob_deleter_middle_crash", {
+      m_mtr.wait_for_flush();
+      DBUG_SUICIDE();
+    });
   }
 
   return (err);

storage/innobase/lob/lob0first.cc

@@ -359,6 +359,9 @@ buf_block_t *first_page_t::load_x(const page_id_t &page_id,
     case FIL_PAGE_SDI_ZBLOB:
     case FIL_PAGE_SDI_BLOB:
       /* Valid first page type.*/
+    case FIL_PAGE_TYPE_ZBLOB2:
+      /* Because of partially purged ZBLOB, we might see this page type as
+         the first page of the ZBLOB. */
       break;
     default:
       std::cerr << "Unexpected LOB first page type=" << page_type << std::endl;

storage/innobase/lob/lob0purge.cc

@@ -449,8 +449,10 @@ void purge(DeleteContext *ctx, dict_index_t *index, trx_id_t trxid,
   page_type_t page_type =
       first_page_t::get_page_type(index, page_id, page_size);
 
-  if (page_type == FIL_PAGE_TYPE_ZBLOB || page_type == FIL_PAGE_TYPE_BLOB ||
-      page_type == FIL_PAGE_SDI_BLOB || page_type == FIL_PAGE_SDI_ZBLOB) {
+  if (page_type == FIL_PAGE_TYPE_ZBLOB ||
+      page_type == FIL_PAGE_TYPE_ZBLOB2 || /* Partially purged ZBLOB */
+      page_type == FIL_PAGE_TYPE_BLOB || page_type == FIL_PAGE_SDI_BLOB ||
+      page_type == FIL_PAGE_SDI_ZBLOB) {
     lob::Deleter free_blob(*ctx);
     free_blob.destroy();
     return;

storage/innobase/lob/zlob0read.cc

@@ -90,14 +90,11 @@ ulint z_read(ReadContext *ctx, lob::ref_t ref, ulint offset, ulint len,
     return (reader.length());
   }
 
-  ut_ad(page_type == FIL_PAGE_TYPE_ZLOB_FIRST);
-
   if (page_type != FIL_PAGE_TYPE_ZLOB_FIRST) {
-    /* In the optimized build, assume that the BLOB has been freed and return
-    without taking further action.  This condition is hit when there are stale
-    LOB references in the clustered index record, especially when there are
-    server crashes during updation of delete-marked clustered index record
-    with external fields. */
+    /* Assume that the BLOB has been freed and return without taking further
+    action.  This condition is hit when there are stale LOB references in the
+    clustered index record, especially when there are server crashes during
+    updation of delete-marked clustered index record with external fields. */
     mtr_commit(&mtr);
     return (0);
   }

storage/innobase/mtr/mtr0mtr.cc

@@ -879,5 +879,10 @@ void mtr_commit_mlog_test_filling_block(log_t &log, size_t req_space_left) {
   mtr_commit_mlog_test_filling_block_low(log, req_space_left, 1);
 }
 
+void mtr_t::wait_for_flush() {
+  ut_ad(commit_lsn() > 0);
+  log_write_up_to(*log_sys, commit_lsn(), true);
+}
+
 #endif /* UNIV_DEBUG */
 #endif /* !UNIV_HOTBACKUP */