pre_split_regions doesn't work with partition table

[darkelf21cn]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   CREATE TABLE partition_table (
   task_id BIGINT NOT NULL,
   creation_dt TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
   result_data JSON
   )
   shard_row_id_bits = 4
   pre_split_regions = 3
   PARTITION BY RANGE (UNIX_TIMESTAMP(creation_dt) ) (
   PARTITION 20200101 VALUES LESS THAN (UNIX_TIMESTAMP('2020-01-01 00:00:00')),
   PARTITION 20200102 VALUES LESS THAN (UNIX_TIMESTAMP('2020-01-02 00:00:00')),
   PARTITION 20200103 VALUES LESS THAN (UNIX_TIMESTAMP('2020-01-03 00:00:00'))
   );
   SHOW TABLE partition_table REGIONS;

2. What did you expect to see?
   I expect to see number_of_partitions * 2 ^ pre_split_regions regions are created with the table creation. So in my test case, I expect to see 3 * 8 = 24 regions are created.

3. What did you see instead?
   Only 3 regions are created, one for each partition.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?
   Release Version: v3.0.8↵Git Commit Hash: 8f13cf1↵Git Branch: HEAD↵UTC Build Time: 2019-12-31 11:14:59↵GoVersion: go version go1.13 linux/amd64↵Race Enabled: false↵TiKV Min Version: v3.0.0-60965b006877ca7234adaced7890d7b029ed1306↵Check Table Before Drop: false

[crazycs520]

@darkelf21cn Thanks for your report, We will fix this soon.

Currently, you can use SPLIT TABLE syntax to solve this problem. such as:

split table partition_table between (0) and (9223372036854775807) regions 8;

[bb7133]

Hi @crazycs520 , I put this bugfix in milestone 3.0.10, please check if this is OK.