Fix crashes in autoincrement code paths (#794) (#794)

Summary:
There are two issues related to autoincrement that can lead to crashes:

1. The max value for double/float type for autoincrement was not implemented in MyRocks, and can lead to assertions. The fix is to add them in.
2. If we try to set auto_increment via alter table on a table without an auto_increment column defined, we segfault because there is no index from which to read the last value. The fix is to perform a check to see if autoincrement exists before reading from index (similar to code ha_rocksdb::open).

Fixes #792
Closes #794

Differential Revision: D6995096

Pulled By: lth

mysql-test/suite/rocksdb/r/autoinc_vars.result

@@ -141,3 +141,13 @@ SELECT * FROM t1;
 a	b
 18446744073709551613	a
 DROP TABLE t1;
+#----------------------------------
+# Issue #792 Crash in autoincrement
+#----------------------------------
+CREATE TABLE t1(C1 DOUBLE AUTO_INCREMENT KEY,C2 CHAR) ENGINE=ROCKSDB;
+INSERT INTO t1 VALUES(2177,0);
+DROP TABLE t1;
+CREATE TABLE t0(c0 BLOB) ENGINE=ROCKSDB;
+INSERT INTO t0 VALUES(0);
+ALTER TABLE t0 AUTO_INCREMENT=0;
+DROP TABLE t0;

mysql-test/suite/rocksdb/t/autoinc_vars.test

@@ -101,3 +101,16 @@ SHOW CREATE TABLE t1;
 INSERT INTO t1 VALUES (NULL, 'c');
 SELECT * FROM t1;
 DROP TABLE t1;
+
+--echo #----------------------------------
+--echo # Issue #792 Crash in autoincrement
+--echo #----------------------------------
+
+CREATE TABLE t1(C1 DOUBLE AUTO_INCREMENT KEY,C2 CHAR) ENGINE=ROCKSDB;
+INSERT INTO t1 VALUES(2177,0);
+DROP TABLE t1;
+
+CREATE TABLE t0(c0 BLOB) ENGINE=ROCKSDB;
+INSERT INTO t0 VALUES(0);
+ALTER TABLE t0 AUTO_INCREMENT=0;
+DROP TABLE t0;

storage/rocksdb/ha_rocksdb.cc

@@ -4730,6 +4730,12 @@ static ulonglong rdb_get_int_col_max_value(const Field *field) {
   case HA_KEYTYPE_LONGLONG:
     max_value = 0x7FFFFFFFFFFFFFFFULL;
     break;
+  case HA_KEYTYPE_FLOAT:
+    max_value = 0x1000000ULL;
+    break;
+  case HA_KEYTYPE_DOUBLE:
+    max_value = 0x20000000000000ULL;
+    break;
   default:
     abort();
   }
@@ -11205,7 +11211,9 @@ bool ha_rocksdb::prepare_inplace_alter_table(
     if (!new_tdef) {
       new_tdef = m_tbl_def;
     }
-    max_auto_incr = load_auto_incr_value_from_index();
+    if (table->found_next_number_field) {
+      max_auto_incr = load_auto_incr_value_from_index();
+    }
   }
 
   ha_alter_info->handler_ctx = new Rdb_inplace_alter_ctx(