Motivation

Table statistics describe the data distribution characteristics of a table. Common statistics include the number of rows, table size, column statistics and more. They are very important for DBMS, especially when executing query plans and optimizing query performance.

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• distinctCount: The number of distinct values.
• min: The minimum value of the column.
• max: The maximum value of the column.
• nullCount: The number of nulls.
• avgLen: Average column length.
• maxLen: Maximum column length.

Storage

snapshot

Add a new filed named statsfield `statistics`  in snapshot to represent the stats file name which store the stats:

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public class Stats {
    private final Long snapshotId;
    private final @Nullable Long mergedRecordCount;
    private final @Nullable Long mergedRecordSize;
    private final @Nullable Map<String, ColStats> colStats;
}

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