Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-518

Statistics: If stat tables get corrupted, queries use wrong statistical data

        Details

        • Type: Bug
        • Status: Closed
        • Priority: Minor
        • Resolution: Fixed
        • Affects Version/s: None
        • Fix Version/s: 10.0.1
        • Component/s: None
        • Labels:
          None

          Description

          From IRC:

          <igor> elenst: could you come up with the test case where e.g. mysql.stat_table is corrupted somehow, then we 1) flush table t1; 2) set use_stat_tables='preferably' 3) run explain select * from t1;
          <igor> elenst: in this case the result of explain is expected the same as we do not use ant stat tables (+ some warning).
          <igor> elenst: I'm afraid now we just have rows == 0 in the explain output with this scenario, which not correct of course.

          The provided test case confirms the suspicion: EXPLAIN shows 0 rows while the real number is 2.

          Test case

          # Run as perl ./mtr <testname>

CREATE TABLE t1 (i INT) ENGINE=MyISAM;
INSERT INTO t1 VALUES (1),(2);
--move_file $MYSQLTEST_VARDIR/mysqld.1/data/mysql/table_stat.MYD $MYSQLTEST_VARDIR/mysqld.1/data/mysql/table_stat.MYD.save

FLUSH TABLES;
SET use_stat_tables=PREFERABLY;

EXPLAIN SELECT * FROM t1;

# Cleanup
--move_file $MYSQLTEST_VARDIR/mysqld.1/data/mysql/table_stat.MYD.save $MYSQLTEST_VARDIR/mysqld.1/data/mysql/table_stat.MYD

SET use_stat_tables=DEFAULT;
DROP TABLE t1;

          Actual result:

          CREATE TABLE t1 (i INT) ENGINE=MyISAM;
INSERT INTO t1 VALUES (1),(2);
FLUSH TABLES;
SET use_stat_tables=PREFERABLY;
EXPLAIN SELECT * FROM t1;
id     select_type     table   type    possible_keys   key     key_len ref     rows    Extra
1      SIMPLE  t1      ALL     NULL    NULL    NULL    NULL    0
Warnings:
Error  29      File './mysql/table_stat.MYD' not found (Errcode: 2)
Error  1017    Can't find file: 'table_stat' (errno: 2)
SET use_stat_tables=DEFAULT;
DROP TABLE t1;

          bzr version-info

          revision-id: elenst@ubuntu11.home-20120903180152-r1n87m6pcvzffh63
date: 2012-09-03 22:01:52 +0400
build-date: 2012-09-09 01:58:25 +0300
revno: 3367

          Workaround: if EXPLAIN produces warnings about corrupted stat tables, set use_stat_tables to NEVER.

            Gliffy Diagrams

              Attachments

                Activity

                Hide
                Permalink
                igor Igor Babaev added a comment -

                The bug was fixed on 11-09-2012 and pushed into maria-5.5-mwl248.

                Show
                igor Igor Babaev added a comment - The bug was fixed on 11-09-2012 and pushed into maria-5.5-mwl248.

                  People

                  • Assignee:
                    igor Igor Babaev
                    Reporter:
                    elenst Elena Stepanova
                  • Votes:
                    0 Vote for this issue
                    Watchers:
                    2 Start watching this issue

                    Dates

                    • Created:
                      Updated:
                      Resolved:

                      Time Tracking

                      Estimated:
                      Original Estimate - Not Specified
                      Not Specified
                      Remaining:
                      Remaining Estimate - 0 minutes
                      0m
                      Logged:
                      Time Spent - 6 hours
                      6h