TiFlash only synchronizes TiDB tables, not the index data on those tables, right?

Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: tiflash只同步tidb的表,不同步该表上的索引数据吧

| username: wenyi

May I ask, does TiFlash only synchronize the tables from TiDB and not the index data on those tables?

| username: tidb菜鸟一只 | Original post link

TiFlash also has indexes, but it shouldn’t be said that they are copied from TiKV. It should be considered as automatically maintained on the table data copied from TiKV.

| username: Kongdom | Original post link

What I understand is that it is not synchronized, and row storage indexes are not suitable for column storage.

| username: wenyi | Original post link

Is the columnar database index a sparse index? For example, StarRocks uses a sparse index that is automatically maintained.

| username: xingzhenxiang | Original post link

TiFlash is columnar storage, so it should not be necessary.

| username: 魔礼养羊 | Original post link

TiFlash does not synchronize row indexes, but it does have column indexes.

Take Excel as an example, and you’ll understand. When we look at an Excel spreadsheet, there are row numbers (1, 2, 3, 4, etc.) and column labels (A, B, C, D, etc.). Typically, we add a “serial number” row.

Now, suppose you have 10,000 rows and 10 columns. If you transpose the columns to rows and rows to columns, this will generate new rows and columns. You will see that the new “rows” only have 10 rows, and the original serial number row becomes an essential field, so synchronization is no longer necessary.

| username: 托马斯滑板鞋 | Original post link

P.S: If it’s a composite index or expression index, I guess it won’t be synchronized.

| username: Running | Original post link

Columnar storage, with each column being indexed data, feels unnecessary.

| username: tidb菜鸟一只 | Original post link

Columnar databases actually store the key of the table and the information of each column for each column, which is essentially equivalent to column indexes on row-based databases, right?