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MDEV-36410: Wrong Result with Desc Primary Key in Index
If a table had a primary_key index, non_primary_key index, and an extended index with primary key in desc order, then the query with where clause predicates containing these index fields was picking an index_merge plan which was causing a wrong result. The plan shouldn't have contained index_merge in the first place, because the rows produced by one index have rows ordered by rowid in ascending order, and the rows coming from the other index were in a different order. The solution is to not produce index_merge plan in such scenarios. is_key_scan_ror() would now return false, for non_primary_key indexes if any primary key part with a reverse sort is present in them.
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‎mysql-test/main/index_merge_innodb_notembedded.result‎

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# MDEV-36410 wrong result with index_merge on indexes having descending primary key
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#
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set optimizer_trace='enabled=on';
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SET @save_sort_buffer_size=@@sort_buffer_size;
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SET SESSION sort_buffer_size = 1024*16;
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id DESC)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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# This must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and `status` =1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ref idx_status,idx_country_code_status_id idx_status 2 const 50 Using where
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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INDEXES
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[
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"idx_status",
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"idx_country_code_status_id"
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]
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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ROR
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[
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true,
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false
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]
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DROP table t1;
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# Now, try with indexes using ASC ordering and PK using DESC
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id DESC),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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# Must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and status = 1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ref idx_status,idx_country_code_status_id idx_status 2 const 50 Using where
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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INDEXES
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[
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"idx_status",
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"idx_country_code_status_id"
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]
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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ROR
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[
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true,
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false
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]
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DROP TABLE t1;
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# Now, try with indexes using DESC ordering and PK using DESC
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id DESC),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id DESC)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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# Must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and status = 1;
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id select_type table type possible_keys key key_len ref rows Extra
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1 SIMPLE t1 ref idx_status,idx_country_code_status_id idx_status 2 const 50 Using where
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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INDEXES
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[
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"idx_status",
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"idx_country_code_status_id"
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]
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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ROR
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[
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true,
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false
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]
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DROP TABLE t1;
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SET sort_buffer_size= @save_sort_buffer_size;

‎mysql-test/main/index_merge_innodb_notembedded.test‎

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--source include/have_innodb.inc
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--source include/have_sequence.inc
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--source include/not_embedded.inc
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--echo
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--echo # MDEV-36410 wrong result with index_merge on indexes having descending primary key
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--echo #
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set optimizer_trace='enabled=on';
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SET @save_sort_buffer_size=@@sort_buffer_size;
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SET SESSION sort_buffer_size = 1024*16;
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id DESC)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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--echo # This must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and `status` =1;
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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#select JSON_DETAILED(JSON_EXTRACT(trace, '$**.range_scan_alternatives[*].index')) AS JS from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
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DROP table t1;
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--echo # Now, try with indexes using ASC ordering and PK using DESC
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id DESC),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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--echo # Must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and status = 1;
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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DROP TABLE t1;
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--echo # Now, try with indexes using DESC ordering and PK using DESC
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CREATE TABLE t1 (
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id bigint(20) NOT NULL,
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title varchar(255) NOT NULL,
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status tinyint(4) DEFAULT 0,
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country_code varchar(5) DEFAULT NULL,
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PRIMARY KEY (id DESC),
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KEY idx_status (status),
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KEY idx_country_code_status_id (country_code,status,id DESC)
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) ENGINE=InnoDB;
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INSERT INTO t1(id,title,status,country_code)
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SELECT seq, CONCAT('abc', seq), seq%10, CONCAT('C', seq%5) FROM seq_1_to_500;
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--echo # Must not use index_merge:
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EXPLAIN
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SELECT * FROM t1 WHERE country_code ='C1' and status = 1;
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set @trace= (select JSON_EXTRACT(trace, '$**.range_scan_alternatives[*]')
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from INFORMATION_SCHEMA.OPTIMIZER_TRACE);
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select json_detailed(json_extract(@trace, '$[*].index')) as INDEXES;
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select json_detailed(json_extract(@trace, '$[*].rowid_ordered')) as ROR;
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DROP TABLE t1;
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SET sort_buffer_size= @save_sort_buffer_size;
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‎sql/opt_range.cc‎

Lines changed: 28 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -11931,22 +11931,44 @@ static bool is_key_scan_ror(PARAM *param, uint keynr, uint8 nparts)
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return FALSE;
1193211932
}
1193311933

11934-
/*
11935-
If there are equalities for all key parts, it is a ROR scan. If there are
11936-
equalities all keyparts and even some of key parts from "Extended Key"
11937-
index suffix, it is a ROR-scan, too.
11938-
*/
1193911934
if (key_part >= key_part_end)
1194011935
return TRUE;
1194111936

11942-
key_part= table_key->key_part + nparts;
1194311937
pk_number= param->table->s->primary_key;
1194411938
if (!param->table->file->pk_is_clustering_key(pk_number))
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return FALSE;
1194611940

11941+
if (keynr == pk_number)
11942+
return TRUE; /* Scan on clustered PK is always ROR */
11943+
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1194711945
KEY_PART_INFO *pk_part= param->table->key_info[pk_number].key_part;
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KEY_PART_INFO *pk_part_end= pk_part +
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param->table->key_info[pk_number].user_defined_key_parts;
11948+
/*
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Check for columns indexed with DESC.
11950+
If a column is present in both Secondary Key and Primary Key and either of
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indexes include it with DESC, then the scan is not a ROR scan.
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*/
11953+
for (; key_part != key_part_end; ++key_part)
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{
11955+
pk_part= param->table->key_info[pk_number].key_part;
11956+
for (; pk_part != pk_part_end; ++pk_part)
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{
11958+
if (key_part->fieldnr == pk_part->fieldnr &&
11959+
(MY_TEST(key_part->key_part_flag & HA_REVERSE_SORT) ||
11960+
MY_TEST(pk_part->key_part_flag & HA_REVERSE_SORT)))
11961+
return FALSE;
11962+
}
11963+
}
11964+
11965+
/*
11966+
If there are equalities for all key parts, it is a ROR scan. If there are
11967+
equalities all keyparts and even some of key parts from "Extended Key"
11968+
index suffix, it is a ROR-scan, too.
11969+
*/
11970+
key_part= table_key->key_part + nparts;
11971+
pk_part= param->table->key_info[pk_number].key_part;
1195011972
for (;(key_part!=key_part_end) && (pk_part != pk_part_end);
1195111973
++key_part, ++pk_part)
1195211974
{

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