2022-09-05 mysql/stonedb-物理存储层-DPN解析

摘要:

DPN作为PACK的元数据，对下用于访问具体的PACK，对上形成知识网格，在整个逻辑关系中，DPN的数据对于数据的访问起到了中枢的作用。

本文对DPN的数据结构的使用关系做说明。

DPN的数据成员:

  uint8_t used : 1;    // occupied or not
  uint8_t local : 1;   // owned by a write transaction, thus to-be-commit
  uint8_t synced : 1;  // if the pack data in memory is up to date with the
                       // version on disk
  uint8_t null_compressed : 1;
  uint8_t data_compressed : 1;
  uint8_t no_compress : 1;
  uint8_t padding[3];
  uint32_t base;       // index of the DPN from which we copied, used by local pack
  uint64_t addr;       // data start address
  uint64_t len;        // data length
  uint32_t nr;         // number of records
  uint32_t nn;         // number of nulls
  common::TX_ID xmin;  // creation trx id
  common::TX_ID xmax;  // delete trx id
  union {
    int64_t min_i;
    double min_d;
    char min_s[8];
  };
  union {
    int64_t max_i;