database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-08-08 11:22:35 +03:00
Code Activity

Better comments

Browse Source
This commit is contained in:
Sergei Petrunia
2015-03-24 13:22:03 +03:00
parent 1626e0d3d4
commit b273e4a5c0
1 changed files with 39 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

43
sql/sql_explain.h
View File

@@ -15,6 +15,43 @@
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/*
== EXPLAIN/ANALYZE architecture ==
=== [SHOW] EXPLAIN data ===
Query optimization produces two data structures:
1. execution data structures themselves (eg. JOINs, JOIN_TAB, etc, etc)
2. Explain data structures.
#2 are self contained set of data structures that has sufficient info to
produce output of SHOW EXPLAIN, EXPLAIN [FORMAT=JSON], or
ANALYZE [FORMAT=JSON], without accessing the execution data structures.
(the only exception is that Explain data structures keep Item* pointers,
and we require that one might call item->print(QT_EXPLAIN) when printing
FORMAT=JSON output)
=== ANALYZE data ===
EXPLAIN data structures have embedded ANALYZE data structures. These are
objects that are used to track how the parts of query plan were executed:
how many times each part of query plan was invoked, how many rows were
read/returned, etc.
Each execution data structure keeps a direct pointer to its ANALYZE data
structure. It is needed so that execution code can quickly increment the
counters.
(note that this increases the set of data that is frequently accessed
during the execution. What is the impact of this?)
Since ANALYZE/EXPLAIN data structures are separated from execution data
structures, it is easy to have them survive until the end of the query,
where we can return ANALYZE [FORMAT=JSON] output to the user, or print
it into the slow query log.
*/
class String_list: public List<char>
{
public:
@@ -43,7 +80,6 @@ public:
ha_rows r_scans; /* How many scans were ran on this join_tab */
ha_rows r_rows; /* How many rows we've got after that */
// ha_rows r_rows_after_table_cond; /* Rows after applying the table condition */
ha_rows r_rows_after_where; /* Rows after applying attached part of WHERE */
bool has_scans() { return (r_scans != 0); }
@@ -103,7 +139,7 @@ public:
{ tracker->stop_tracking(); }
/*
A class for tracking execution time
A class for tracking time it takes to do a certain action
*/
class Exec_time_tracker
{
@@ -127,7 +163,6 @@ public:
}
// interface for getting the time
//loops, starts, stops
ulonglong get_loops() { return count; }
double get_time_ms()
{
@@ -710,7 +745,7 @@ public:
// Valid if ET_USING tag is present
Explain_quick_select *quick_info;
/* Non-NULL values means this tab uses "range checked for each record" */
/* Non-NULL value means this tab uses "range checked for each record" */
Explain_range_checked_fer *range_checked_fer;
bool full_scan_on_null_key;