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How do I check whether my storage completed reformatting after an upgrade from v6.x to v7.x?
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To know which tables/columns are still in the old format and need to be merged is through looking for their encoding mechanism.
Check the encoding column in information_schema.columnar_segments and see if "String", "StringRunLength", "LZ4", "IntegerDelta", "IntegerRunLength" appear (those are the ones we changed in 7.x, into "SeekableString", "SeekableStringRunLength", etc). i.e. Seek* encoding is 7.x, rest is 6.x.
Use the following query:
SELECT DATABASE_NAME, TABLE_ NAME, ENCODING from information_schema.COLUMNAR_SEGMENTS;
You may find more information here.
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