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Debugging: add dbug_print_join_prefix() to use in best_access_path

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A call to

  dbug_print_join_prefix(join_positions, idx, s)

returns a const char* ponter to string with current join prefix,
including the table being added to it.
This commit is contained in:
Sergei Petrunia 2024-09-22 21:35:19 +03:00
parent 42eb64e64d
commit d67c88946f
1 changed files with 32 additions and 0 deletions
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32
sql/sql_select.cc
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@ -7550,6 +7550,30 @@ double adjust_quick_cost(double quick_cost, ha_rows records)
}
#ifndef DBUG_OFF
char dbug_join_prefix_buf[256];
const char* dbug_print_join_prefix(const POSITION *join_positions,
uint idx,
JOIN_TAB *s)
{
char *buf= dbug_join_prefix_buf;
String str(buf, sizeof(dbug_join_prefix_buf), &my_charset_bin);
str.length(0);
for (uint i=0; i!=idx; i++)
{
str.append(join_positions[i].table->table->alias);
str.append(',');
}
str.append(s->table->alias);
if (str.c_ptr_safe() == buf)
return buf;
else
return "Couldn't fit into buffer";
}
#endif
/**
Find the best access path for an extension of a partial execution
plan and add this path to the plan.
@ -7573,6 +7597,14 @@ double adjust_quick_cost(double quick_cost, ha_rows records)
@param pos OUT Table access plan
@param loose_scan_pos OUT Table plan that uses loosescan, or set cost to
DBL_MAX if not possible.
@detail
Use this to print the current join prefix:
dbug_print_join_prefix(join_positions, idx, s)
Use this as breakpoint condition to stop at join prefix "t1,t2,t3":
$_streq(dbug_print_join_prefix(join_positions, idx, s), "t1,t2,t3")
@return
None