Clickhouse: Insert the same data to ReplicatedMergeTree table but get only one record when select.

[AlexanderJLiu]

Describe the bug

Insert the same data to ReplicatedMergeTree table but get only one record when select.

How to reproduce

• Which ClickHouse server version to use: 20.3.7.46

• Create table

  CREATE TABLE olap.replicated_test
  (
      date Date,
      a String,
      b String
  )
  ENGINE = ReplicatedMergeTree('/clickhouse/tables/{shard}/replicated_test', '{replica}')
  PARTITION BY toYYYYMM(date)
  ORDER BY (date, a, b)
  SETTINGS index_granularity = 8192;
  

• Insert data and select

  insert into olap.replicated_test values('2020-06-01', 'a', 'b');
  select * from olap.replicated_test;
  

  ┌───────date─┬─a─┬─b─┐
  │ 2020-06-01 │ a │ b │
  └────────────┴───┴───┘
  

• Insert the same data again and select

  insert into olap.replicated_test values('2020-06-01', 'a', 'b');
  select * from olap.replicated_test;
  

  ┌───────date─┬─a─┬─b─┐
  │ 2020-06-01 │ a │ b │
  └────────────┴───┴───┘
  

[den-crane]

That's how insert deduplication works.

https://clickhouse.tech/docs/en/engines/table-engines/mergetree-family/replication/

_Data blocks are deduplicated. For multiple writes of the same data block (data blocks of the same size containing the same rows in the same order), the block is only written once. The reason for this is in case of network failures when the client application doesn’t know if the data was written to the DB, so the INSERT query can simply be repeated. It doesn’t matter which replica INSERTs were sent to with identical data. INSERTs are idempotent. Deduplication parameters are controlled by merge_tree server settings._

https://clickhouse.tech/docs/en/operations/settings/settings/#settings-insert-deduplicate