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MDEV-3798: EXPLAIN UPDATE/DELETE

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- Produce correct #rows for ORDER BY ... LIMIT N queries that take advantage of 
  ordered index read to read only N rows.
This commit is contained in:
Sergey Petrunya
2013-10-09 13:07:46 +04:00
parent 161d687594
commit 3c6ac6694d
6 changed files with 32 additions and 14 deletions
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12
sql/sql_update.cc
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@@ -456,6 +456,7 @@ int mysql_update(THD *thd,
table->update_const_key_parts(conds);
order= simple_remove_const(order, conds);
query_plan.scanned_rows= select? select->records: table->file->stats.records;
if (select && select->quick && select->quick->unique_key_range())
{ // Single row select (always "ordered"): Ok to use with key field UPDATE
@@ -465,8 +466,12 @@ int mysql_update(THD *thd,
}
else
{
ha_rows scanned_limit= query_plan.scanned_rows;
query_plan.index= get_index_for_order(order, table, select, limit,
&need_sort, &reverse);
&scanned_limit, &need_sort, &reverse);
if (!need_sort)
query_plan.scanned_rows= scanned_limit;
if (select && select->quick)
{
DBUG_ASSERT(need_sort || query_plan.index == select->quick->index);
@@ -492,7 +497,6 @@ int mysql_update(THD *thd,
- if we're running EXPLAIN UPDATE, get out
*/
query_plan.select= select;
query_plan.table_rows= table->file->stats.records;
query_plan.possible_keys= select? select->possible_keys: key_map(0);
if (used_key_is_modified || order ||
@@ -504,7 +508,6 @@ int mysql_update(THD *thd,
query_plan.using_io_buffer= true;
}
query_plan.save_explain_data(thd->lex->explain);
/*
Ok, we have generated a query plan for the UPDATE.
@@ -513,6 +516,8 @@ int mysql_update(THD *thd,
*/
if (thd->lex->describe)
goto exit_without_my_ok;
query_plan.save_explain_data(thd->lex->explain);
thd->apc_target.enable();
apc_target_enabled= true;
DBUG_EXECUTE_IF("show_explain_probe_update_exec_start",
@@ -1041,6 +1046,7 @@ err:
exit_without_my_ok:
DBUG_ASSERT(!apc_target_enabled);
query_plan.save_explain_data(thd->lex->explain);
int err2= thd->lex->explain->send_explain(thd);