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This race condition is hard to reproduce with unmodified code. But it is easily reproducible with error simulation as in the following patch:
diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
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index c60ef6f..d10dc3d 100644
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--- a/sql/sql_insert.cc
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+++ b/sql/sql_insert.cc
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@@ -3021,7 +3021,7 @@ bool Delayed_insert::handle_inserts(void)
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table->use_all_columns();
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thd_proc_info(&thd, "upgrading lock");
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- if (thr_upgrade_write_delay_lock(*thd.lock->locks, delayed_lock,
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+ if (1 || thr_upgrade_write_delay_lock(*thd.lock->locks, delayed_lock,
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thd.variables.lock_wait_timeout))
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{
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/*
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MTR test case:
CREATE TABLE t1(a INT);
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let $i= 10000;
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disable_query_log;
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while ($i)
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{
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--error 0,1150
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INSERT DELAYED INTO t1 VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11),(12),(13),(14),(15),(16),(17),(18),(19),(20);
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dec $i;
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}
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enable_query_log;
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DROP TABLE t1;
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Running this test makes threads stuck as following:
+------+---------+-----------+------+---------+------+----------------------------+------------------------------------------------------------------------------------------------------+----------+
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| Id | User | Host | db | Command | Time | State | Info | Progress |
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+------+---------+-----------+------+---------+------+----------------------------+------------------------------------------------------------------------------------------------------+----------+
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| 2 | root | localhost | test | Query | 261 | waiting for handler insert | INSERT DELAYED INTO t1 VALUES(1),(2),(3),(4),(5),(6),(7),(8),(9),(10),(11),(12),(13),(14),(15),(16), | 0.000 |
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| 5026 | root | localhost | NULL | Query | 0 | NULL | show processlist | 0.000 |
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| 8018 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8025 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8028 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8029 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8043 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8056 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8150 | DELAYED | localhost | test | Killed | 263 | upgrading lock | | 0.000 |
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| 8170 | DELAYED | localhost | test | Killed | 262 | upgrading lock | | 0.000 |
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| 8207 | DELAYED | localhost | test | Killed | 262 | upgrading lock | | 0.000 |
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| 8243 | DELAYED | localhost | test | Killed | 262 | upgrading lock | | 0.000 |
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| 8295 | DELAYED | localhost | test | Killed | 261 | upgrading lock | | 0.000 |
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| 8305 | DELAYED | localhost | test | Killed | 261 | upgrading lock | | 0.000 |
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+------+---------+-----------+------+---------+------+----------------------------+------------------------------------------------------------------------------------------------------+----------+
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The following patch makes it work:
diff --git a/sql/sql_insert.cc b/sql/sql_insert.cc
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index c60ef6f..d10dc3d 100644
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--- a/sql/sql_insert.cc
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+++ b/sql/sql_insert.cc
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@@ -3238,6 +3238,7 @@ bool Delayed_insert::handle_inserts(void)
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max_rows= 0; // For DBUG output
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#endif
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/* Remove all not used rows */
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+ mysql_mutex_lock(&mutex);
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while ((row=rows.get()))
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{
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if (table->s->blob_fields)
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@@ -3254,7 +3255,6 @@ bool Delayed_insert::handle_inserts(void)
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}
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DBUG_PRINT("error", ("dropped %lu rows after an error", max_rows));
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thread_safe_increment(delayed_insert_errors, &LOCK_delayed_status);
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- mysql_mutex_lock(&mutex);
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DBUG_RETURN(1);
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}
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#endif /* EMBEDDED_LIBRARY */
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