From dd0e62b34d2e409e2c8430c718dc005a58d6792e Mon Sep 17 00:00:00 2001
From: Brandon Nesterenko <brandon.nesterenko@mariadb.com>
Date: Mon, 14 Jun 2021 18:38:31 -0600
Subject: MDEV-20219: PURGE BINARY LOGS does not always purge

THIS COMMIT IS FOR DEMONSTRATION ONLY

PURGE BINARY LOGS (as intended) does not purge logs
that are open. When one thread is reading the logs, for
example via SHOW BINLOG EVENTS, then an issued
PURGE command will not delete the log while it is open
by SHOW. This commit provides a test/result to demonstrate
this behavior. With respect to MDEV-20219, the code inside
of the backup utility has a comment before purging stating
//be carefull with this step if you have slaves!
which leads me to believe this issue is due to the above
behavior.
---
 .../purge_not_deleting_on_concurrent_reads.result  | 23 +++++++++++++++++
 .../t/purge_not_deleting_on_concurrent_reads.test  | 30 ++++++++++++++++++++++
 sql/sql_repl.cc                                    |  2 ++
 3 files changed, 55 insertions(+)
 create mode 100644 mysql-test/suite/binlog/r/purge_not_deleting_on_concurrent_reads.result
 create mode 100644 mysql-test/suite/binlog/t/purge_not_deleting_on_concurrent_reads.test

diff --git a/mysql-test/suite/binlog/r/purge_not_deleting_on_concurrent_reads.result b/mysql-test/suite/binlog/r/purge_not_deleting_on_concurrent_reads.result
new file mode 100644
index 00000000000..84890dd2285
--- /dev/null
+++ b/mysql-test/suite/binlog/r/purge_not_deleting_on_concurrent_reads.result
@@ -0,0 +1,23 @@
+connect con1,localhost,root,,;
+FLUSH LOGS;
+FLUSH LOGS;
+FLUSH LOGS;
+PURGE BINARY LOGS to 'master-bin.000004';
+FLUSH LOGS;
+connect con2,localhost,root,,;
+SET DEBUG_SYNC= "show_binlog_events_got_linfo WAIT_FOR purge_finished";
+SHOW BINLOG EVENTS;
+connection con1;
+PURGE BINARY LOGS to 'master-bin.000005';
+SET DEBUG_SYNC= "now SIGNAL purge_finished";
+connection con2;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+master-bin.000004	4	Format_desc	1	256	Server ver: 10.3.30-MariaDB-debug-log, Binlog ver: 4
+master-bin.000004	256	Gtid_list	1	285	[]
+master-bin.000004	285	Binlog_checkpoint	1	329	master-bin.000003
+master-bin.000004	329	Binlog_checkpoint	1	373	master-bin.000004
+master-bin.000004	373	Rotate	1	421	master-bin.000005;pos=4
+# -- Index File:
+./master-bin.000004
+./master-bin.000005
+SET debug_sync = 'reset';
diff --git a/mysql-test/suite/binlog/t/purge_not_deleting_on_concurrent_reads.test b/mysql-test/suite/binlog/t/purge_not_deleting_on_concurrent_reads.test
new file mode 100644
index 00000000000..c5c8b869569
--- /dev/null
+++ b/mysql-test/suite/binlog/t/purge_not_deleting_on_concurrent_reads.test
@@ -0,0 +1,30 @@
+--source include/have_debug.inc
+--source include/have_debug_sync.inc
+
+--source include/have_binlog_format_row.inc
+
+connect(con1,localhost,root,,);
+FLUSH LOGS;
+FLUSH LOGS;
+FLUSH LOGS;
+PURGE BINARY LOGS to 'master-bin.000004';
+FLUSH LOGS;
+
+connect(con2,localhost,root,,);
+SET DEBUG_SYNC= "show_binlog_events_got_linfo WAIT_FOR purge_finished";
+--send SHOW BINLOG EVENTS
+
+--connection con1
+PURGE BINARY LOGS to 'master-bin.000005';
+SET DEBUG_SYNC= "now SIGNAL purge_finished";
+
+--connection con2
+--reap
+
+--let $datadir= `SELECT @@datadir`
+--let $index=$datadir/mysqld-bin.index
+--echo # -- Index File:
+--cat_file $index
+
+
+SET debug_sync = 'reset';
\ No newline at end of file
diff --git a/sql/sql_repl.cc b/sql/sql_repl.cc
index 389346e389d..6c16e5b6c46 100644
--- a/sql/sql_repl.cc
+++ b/sql/sql_repl.cc
@@ -4015,6 +4015,8 @@ bool mysql_show_binlog_events(THD* thd)
 
     thd->current_linfo= &linfo;
 
+    DEBUG_SYNC(thd, "show_binlog_events_got_linfo");
+
     if ((file=open_binlog(&log, linfo.log_file_name, &errmsg)) < 0)
       goto err;
 
-- 
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