MDEV-12465: Server crashes in my_scan_weight_utf8_bin upon collecting stats for RocksDB table

Apply patch by Oleksandr Byelkin:
Do not use "only index read" in analyzing indices if there is a field which present in the index only partially.

sql/sql_statistics.cc

@@ -1801,6 +1801,7 @@ class Index_prefix_calc: public Sql_alloc
 public:
 
   bool is_single_comp_pk;
+  bool is_partial_fields_present;
 
   Index_prefix_calc(THD *thd, TABLE *table, KEY *key_info)
     : index_table(table), index_info(key_info)
@@ -1812,7 +1813,7 @@ class Index_prefix_calc: public Sql_alloc
     prefixes= 0;
     LINT_INIT_STRUCT(calc_state);
 
-    is_single_comp_pk= FALSE;
+    is_partial_fields_present= is_single_comp_pk= FALSE;
     uint pk= table->s->primary_key;
     if ((uint) (table->key_info - key_info) == pk &&
         table->key_info[pk].user_defined_key_parts == 1)
@@ -1834,7 +1835,10 @@ class Index_prefix_calc: public Sql_alloc
           calculating the values of 'avg_frequency' for prefixes.
 	*/   
         if (!key_info->key_part[i].field->part_of_key.is_set(keyno))
+        {
+          is_partial_fields_present= TRUE;
           break;
+        }
 
         if (!(state->last_prefix=
               new (thd->mem_root) Cached_item_field(thd,
@@ -2633,7 +2637,13 @@ int collect_statistics_for_index(THD *thd, TABLE *table, uint index)
     DBUG_RETURN(rc);
   }
 
-  table->file->ha_start_keyread(index);
+  /*
+    Request "only index read" in case of absence of fields which are
+    partially in the index to avoid problems with partitioning (for example)
+    which want to get whole field value.
+  */
+  if (!index_prefix_calc.is_partial_fields_present)
+    table->file->ha_start_keyread(index);
   table->file->ha_index_init(index, TRUE);
   rc= table->file->ha_index_first(table->record[0]);
   while (rc != HA_ERR_END_OF_FILE)

storage/rocksdb/mysql-test/rocksdb/r/analyze_table.result

@@ -27,3 +27,29 @@ ANALYZE TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	analyze	status	OK
 DROP TABLE t1;
+#
+# MDEV-12465: Server crashes in my_scan_weight_utf8_bin upon
+# collecting stats for RocksDB table
+#
+CREATE TABLE t1 (
+pk INT,
+f1 CHAR(255),
+f2 TEXT,
+f3 VARCHAR(255),
+f4 TEXT,
+PRIMARY KEY (pk),
+KEY (f4(255))
+) ENGINE=RocksDB
+CHARSET utf8
+COLLATE utf8_bin
+PARTITION BY KEY (pk) PARTITIONS 2;
+INSERT INTO t1 VALUES
+(1,'foo','bar','foo','bar'), (2,'bar','foo','bar','foo');
+ANALYZE TABLE t1 PERSISTENT FOR ALL;
+Table	Op	Msg_type	Msg_text
+test.t1	analyze	status	Engine-independent statistics collected
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 'f2'
+test.t1	analyze	Warning	Engine-independent statistics are not collected for column 'f4'
+test.t1	analyze	status	OK
+drop table t1;
+# End of 10.2 tests

storage/rocksdb/mysql-test/rocksdb/t/analyze_table.test

 --source include/have_rocksdb.inc
+--source include/have_partition.inc
 
 # 
 # ANALYZE TABLE statements
@@ -29,3 +30,28 @@ INSERT INTO t1 VALUES (5,8),(6,10),(7,11),(8,12);
 ANALYZE TABLE t1;
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-12465: Server crashes in my_scan_weight_utf8_bin upon
+--echo # collecting stats for RocksDB table
+--echo #
+
+CREATE TABLE t1 (
+  pk INT,
+  f1 CHAR(255),
+  f2 TEXT,
+  f3 VARCHAR(255),
+  f4 TEXT,
+  PRIMARY KEY (pk),
+  KEY (f4(255))
+) ENGINE=RocksDB
+  CHARSET utf8
+  COLLATE utf8_bin
+  PARTITION BY KEY (pk) PARTITIONS 2;
+INSERT INTO t1 VALUES
+(1,'foo','bar','foo','bar'), (2,'bar','foo','bar','foo');
+
+ANALYZE TABLE t1 PERSISTENT FOR ALL;
+
+drop table t1;
+
+--echo # End of 10.2 tests