swuferhong commented on code in PR #2650: URL: https://github.com/apache/fluss/pull/2650#discussion_r2792416233
########## website/docs/table-design/auto_increment.md: ########## @@ -0,0 +1,73 @@ +--- +sidebar_label: Auto-Increment Column +title: Auto-Increment Column +sidebar_position: 6 +--- + +# Auto-Increment Column + +## Introduction + +In Fluss, the auto increment column is a feature that automatically generates a unique numeric value, commonly used to create unique identifiers for each row of data. +Each time a new record is inserted, the auto increment column automatically assigns an incrementing value, eliminating the need for manually specifying the number. + +One application scenario is of the auto-increment column is to accelerate the counting of distinct values in a high-cardinality column: +an auto-increment column can be used to represent the unique value column in a dictionary. +Compared to directly counting distinct STRING values, counting distinct integer values of the auto-increment column can sometimes improve the query speed by several times or even tens of times. + +## Basic features + +### Uniqueness + +Fluss guarantees table-wide uniqueness for values it generates in the auto-increment column. + +### Monotonicity +In order to improve the performance of allocating auto-incremented IDs, each table bucket on TabletServers caches some auto-incremented IDs locally. +In this situation, Fluss cannot guarantee that the values for the auto-increment column are strictly monotonic. +It can only be ensured that the values roughly increase in chronological order. + +:::note +The number of auto-incremented IDs cached by the TabletServers is determined by the parameter table.auto-increment.cache-size, which defaults to 100,000. +::: + +For example, create a table named test_tbl3 with 2 buckets and insert five rows of data as follows: + +```sql +CREATE TABLE test_tbl +( + id BIGINT, + number BIGINT, + PRIMARY KEY (id) NOT ENFORCED +) WITH ( + 'auto-increment.fields' = 'number', + 'bucket.num' = '2' +); + +INSERT INTO test_tbl VALUES (1); +INSERT INTO test_tbl VALUES (2); +INSERT INTO test_tbl VALUES (3); +INSERT INTO test_tbl VALUES (4); +INSERT INTO test_tbl VALUES (5); +``` + +The auto-incremented IDs in the table test_tbl do not monotonically increase, because the two table buckets cache auto-incremented IDs, [1, 100000] and [100001, 200000], respectively. + +```sql +SELECT * FROM test_tbl ORDER BY id; ++------+--------+ +| id | number | ++------+--------+ +| 1 | 1 | +| 2 | 100001 | +| 3 | 200001 | Review Comment: 3 200001？ this table only have two bucket. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
