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MDEV-5492 - Reduce usage of LOCK_open: TABLE::in_use

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Move TABLE::in_use out of LOCK_open.

This is done with assumtion that foreign threads accessing TABLE::in_use
will only need consistent value _after_ marking table for flush and purging
unused table instances. In this case TABLE::in_use will always point to a
valid thread object.

Previously FLUSH TABLES thread may wait for tables flushed subsequently by
concurrent threads which breaks the above assumption, e.g.:
open tables: t1 (version= 1)
thr1 (FLUSH TABLES): refresh_version++
thr1 (FLUSH TABLES): purge table cache
open tables: none
thr2 (SELECT * FROM t1): open tables: t1
open tables: t1 (version= 2)
thr2 (FLUSH TABLES): refresh_version++
thr2 (FLUSH TABLES): purge table cache
thr1 (FLUSH TABLES): wait for old tables (including t1 with version 2)

It is fixed so that FLUSH TABLES waits only for tables that were open
heretofore.
This commit is contained in:
Sergey Vojtovich
2014-02-13 10:44:10 +04:00
parent a25d87e50f
commit 048e9c40a6
8 changed files with 83 additions and 120 deletions
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10
sql/table.cc
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@@ -3805,7 +3805,7 @@ bool TABLE_SHARE::visit_subgraph(Wait_for_flush *wait_for_flush,
bool result= TRUE;
/*
To protect used_tables list from being concurrently modified
To protect all_tables list from being concurrently modified
while we are iterating through it we acquire LOCK_open.
This does not introduce deadlocks in the deadlock detector
because we won't try to acquire LOCK_open while
@@ -3832,7 +3832,8 @@ bool TABLE_SHARE::visit_subgraph(Wait_for_flush *wait_for_flush,
while ((table= tables_it++))
{
if (table->in_use && gvisitor->inspect_edge(&table->in_use->mdl_context))
DBUG_ASSERT(table->in_use && tdc.flushed);
if (gvisitor->inspect_edge(&table->in_use->mdl_context))
{
goto end_leave_node;
}
@@ -3841,7 +3842,8 @@ bool TABLE_SHARE::visit_subgraph(Wait_for_flush *wait_for_flush,
tables_it.rewind();
while ((table= tables_it++))
{
if (table->in_use && table->in_use->mdl_context.visit_subgraph(gvisitor))
DBUG_ASSERT(table->in_use && tdc.flushed);
if (table->in_use->mdl_context.visit_subgraph(gvisitor))
{
goto end_leave_node;
}
@@ -3890,7 +3892,7 @@ bool TABLE_SHARE::wait_for_old_version(THD *thd, struct timespec *abstime,
MDL_wait::enum_wait_status wait_status;
mysql_mutex_assert_owner(&tdc.LOCK_table_share);
DBUG_ASSERT(has_old_version());
DBUG_ASSERT(tdc.flushed);
tdc.m_flush_tickets.push_front(&ticket);