AMashenkov commented on a change in pull request #330:
URL: https://github.com/apache/ignite-3/pull/330#discussion_r708096914
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File path:
modules/schema/src/main/java/org/apache/ignite/internal/schema/mapping/ColumnMapper.java
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@@ -24,6 +24,7 @@
/**
* Column mapper interface.
*/
+// TODO: IGNITE-15480 Probably should be removed after index column mapping
refactoring.
Review comment:
Assume there is a row R with schema V1.
Then you update schema to V2 and add a column C with a default D1.
Then you update schema to V3 and update default to D2.
Now, you read R, which is stored as of V1 version, and upgrade it to V3.
On one side, R doesn't contains C column, and there is no descriptor for
column C in V1.
On another side, you can't use column C descriptor from V3 because it was
changed in between.
Using column C descriptor from V2 will be correct, but you will need to go
through schema history for that for every row and every column you read just to
check if there is any history.
Column mapper merges schema changes once and then get reused.
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