Help Center/ GaussDB/ Feature Guide(Centralized_8.x)/ Storage Engine/ Ustore/ Overview/ Ustore Features and Specifications/ Storage Specifications
Updated on 2024-06-07 GMT+08:00
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Storage Specifications

  1. The maximum number of columns in a data table is 1600.
  2. Transaction directory (TD) init_td is a unique structure used by Ustore tables to store page transaction information. The number of TDs determines the maximum number of concurrent transactions supported on a page. When creating a table or index, you can specify the initial TD size init_td. The value range is [2,128], and the default value is 4. A single page supports a maximum of 128 concurrent transactions.
  3. The maximum tuple length of a Ustore table (excluding toast) cannot exceed 8192 – MAXALIGN(56 + init_td x 26 + 4), where MAXALIGN indicates 8-byte alignment. When the length of the inserted data exceeds the threshold, you will receive an error reporting that the tuple is too long to be inserted. The impact of init_td on the tuple length is as follows:
    • If the value of init_td is the minimum value 2, the tuple length cannot exceed 8192 – MAXALIGN(56 + 2 x 26 + 4) = 8080 bytes.
    • If the value of init_td is the default value 4, the tuple length cannot exceed 8192 – MAXALIGN(56 + 4 x 26 + 4) = 8024 bytes.
    • If the value of init_td is the maximum value 128, the tuple length cannot exceed 8192 – MAXALIGN(56 + 128 x 26 + 4) = 4800 bytes.
  4. The maximum number of index columns is 32. The maximum number of columns in a global partitioned index is 31.
  5. The length of an index tuple cannot exceed (8192 – MAXALIGN(28 + 3 x 4 + 3 x 10) – MAXALIGN(42))/3, where MAXALIGN indicates 8-byte alignment. When the length of the inserted data exceeds the threshold, you will receive an error reporting that the tuple is too long to be inserted. As for the threshold, the index page header is 28 bytes, row pointer is 4 bytes, tuple CTID+INFO flag is 10 bytes, and page tail is 42 bytes.
  6. The maximum rollback segment size is 16 TB.