From 81243cb239163f9de4b91dab39171ca3b8fc8d35 Mon Sep 17 00:00:00 2001
From: Satya Bodapati <satya.bodapati@percona.com>
Date: Fri, 19 Jun 2020 08:15:13 +0530
Subject: [PATCH] Bug#99935 : innodb_doublewrite_files is not correct when
 innodb_buffer_pool_size > 1G

Problem:
-------
According to documentation, default value of innodb_doublewrite_files is
innodb_buffer_pool_instances * 2

But when you start InnoDB with buffer pool size > 1G (the number of instances
is 8), it still creates 2 files only. Expected files is 16 (8*2)

Fix:
---
Use correct number of dblwr according to the number of buf pool instances
---
 .../suite/innodb/r/dblwr_file_count.result    |  3 +++
 .../innodb/t/dblwr_file_count-master.opt      |  1 +
 .../suite/innodb/t/dblwr_file_count.test      | 22 +++++++++++++++++++
 storage/innobase/buf/buf0dblwr.cc             |  6 +++--
 4 files changed, 30 insertions(+), 2 deletions(-)
 create mode 100644 mysql-test/suite/innodb/r/dblwr_file_count.result
 create mode 100644 mysql-test/suite/innodb/t/dblwr_file_count-master.opt
 create mode 100644 mysql-test/suite/innodb/t/dblwr_file_count.test

diff --git a/mysql-test/suite/innodb/r/dblwr_file_count.result b/mysql-test/suite/innodb/r/dblwr_file_count.result
new file mode 100644
index 00000000000..18ad6ac77f1
--- /dev/null
+++ b/mysql-test/suite/innodb/r/dblwr_file_count.result
@@ -0,0 +1,3 @@
+#
+# BUG#99935 : innodb_doublewrite_files is not correct when innodb_buffer_pool_size > 1G
+#
diff --git a/mysql-test/suite/innodb/t/dblwr_file_count-master.opt b/mysql-test/suite/innodb/t/dblwr_file_count-master.opt
new file mode 100644
index 00000000000..2e001483cad
--- /dev/null
+++ b/mysql-test/suite/innodb/t/dblwr_file_count-master.opt
@@ -0,0 +1 @@
+--innodb_buffer_pool_size=1G
diff --git a/mysql-test/suite/innodb/t/dblwr_file_count.test b/mysql-test/suite/innodb/t/dblwr_file_count.test
new file mode 100644
index 00000000000..d46c93487dc
--- /dev/null
+++ b/mysql-test/suite/innodb/t/dblwr_file_count.test
@@ -0,0 +1,22 @@
+# Test needs 1G min buffer pool size
+--source include/big_test.inc
+
+--echo #
+--echo # BUG#99935 : innodb_doublewrite_files is not correct when innodb_buffer_pool_size > 1G
+--echo #
+
+--let $MYSQLD_DATADIR=`SELECT @@datadir`
+--let $PAGE_SIZE=`SELECT @@innodb_page_size`
+
+--let $max = `SELECT @@innodb_buffer_pool_instances * 2`
+--let $i = 0
+
+while ($i < $max) {
+--let $part1=$MYSQLD_DATADIR/#ib_$PAGE_SIZE
+--let $part2=_$i.dblwr
+--let $file= $part1$part2
+
+--file_exists $file
+
+--inc $i
+}
diff --git a/storage/innobase/buf/buf0dblwr.cc b/storage/innobase/buf/buf0dblwr.cc
index 45fe60f126d..a1c095ed428 100644
--- a/storage/innobase/buf/buf0dblwr.cc
+++ b/storage/innobase/buf/buf0dblwr.cc
@@ -1721,7 +1721,9 @@ dberr_t dblwr::open(bool create_new_db) noexcept {
   uint32_t segments_per_file{};
 
   if (dblwr::n_files == 0) {
-    dblwr::n_files = 2;
+    dblwr::n_files = std::max(2UL, srv_buf_pool_instances * 2);
+  } else if (dblwr::n_files > srv_buf_pool_instances * 2) {
+    dblwr::n_files = srv_buf_pool_instances * 2;
   }
 
   ib::info(ER_IB_MSG_DBLWR_1324)
@@ -1734,7 +1736,7 @@ dberr_t dblwr::open(bool create_new_db) noexcept {
   ib::info(ER_IB_MSG_DBLWR_1323)
       << "Double write buffer pages per instance: " << dblwr::n_pages;
 
-  if (Double_write::s_n_instances < dblwr::n_files) {
+  if (Double_write::s_n_instances <= dblwr::n_files) {
     segments_per_file = 1;
     Double_write::s_files.resize(Double_write::s_n_instances);
   } else {