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take into account table lock mode when opening table:

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try to find most suitable table, to avouid pickup table with too low locking mode or occupy table with write mode for select when it will be need for update later
(BUG#9597)
This commit is contained in:
bell@sanja.is.com.ua
2005-07-15 01:22:14 +03:00
parent a25c4ead10
commit a7834de02d
3 changed files with 63 additions and 4 deletions
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34
sql/sql_base.cc
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@@ -1041,6 +1041,8 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
if (thd->locked_tables || thd->prelocked_mode)
{ // Using table locks
TABLE *best_table= 0;
int best_distance= INT_MIN, distance;
for (table=thd->open_tables; table ; table=table->next)
{
if (table->s->key_length == key_length &&
@@ -1049,11 +1051,37 @@ TABLE *open_table(THD *thd, TABLE_LIST *table_list, MEM_ROOT *mem_root,
table->query_id != thd->query_id && /* skip tables already used by this query */
!(thd->prelocked_mode && table->query_id))
{
table->query_id= thd->query_id;
DBUG_PRINT("info",("Using locked table"));
goto reset;
distance= ((int) table->reginfo.lock_type -
(int) table_list->lock_type);
/*
Find a table that either has the exact lock type requested,
or has the best suitable lock. In case there is no locked
table that has an equal or higher lock than requested,
we still maitain the best_table to produce an error message
about wrong lock mode on the table. The best_table is changed
if bd < 0 <= d or bd < d < 0 or 0 <= d < bd.
distance < 0 - we have not enough high lock mode
distance > 0 - we have lock mode higher then we require
distance == 0 - we have lock mode exactly which we need
*/
if (best_distance < 0 && distance > best_distance ||
distance >= 0 && distance < best_distance)
{
best_distance= distance;
best_table= table;
if (best_distance == 0)
break;
}
}
}
if (best_table)
{
table= best_table;
table->query_id= thd->query_id;
DBUG_PRINT("info",("Using locked table"));
goto reset;
}
/*
is it view?
(it is work around to allow to open view with locked tables,