深入理解MySQL 5.7 GTID系列（二）：GTID相关内部数据结构

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e859a28b-b66d-11e7-8371-000c291f347d:1-5

const time_t save_server_start_time= server_start_time; //获取MySQL   
 启动时间
 server_start_time+= ((ulonglong)current_pid << 48) + current_pid;//加入Lwp号运算
  thd->status_var.bytes_sent= (ulonglong)thd;//这是一个内存指针

  lex_start(thd);
  func_uuid= new (thd->mem_root) Item_func_uuid();
  func_uuid->fixed= 1;
  func_uuid->val_str(&uuid);     //这个函数里面有具体的运算过程

strncpy(server_uuid, uuid.c_ptr(), UUID_LENGTH);

#0  init_server_auto_options () at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:3810
#1  0x0000000000ec625e in mysqld_main (argc=97, argv=0x2e9af08) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/mysqld.cc:4962
#2  0x0000000000ebd604 in main (argc=10, argv=0x7fffffffe458) at /root/mysql5.7.14/percona-server-5.7.14-7/sql/main.cc:25

 /** The number of bytes in the data of a Uuid. */
  static const size_t BYTE_LENGTH= 16;
  /** The data for this Uuid. */
  unsigned char bytes[BYTE_LENGTH];

  /// SIDNO of this Gtid.
  rpl_sidno sidno;
  /// GNO of this Gtid.
  rpl_gno gno;

/// Read-write lock that protects updates to the number of SIDNOs.
  mutable Checkable_rwlock *sid_lock;

  /**
    Array that maps SIDNO to SID; the element at index N points to a
    Node with SIDNO N-1.
  */
  Prealloced_array<Node*, 8, true>_sidno_to_sid; //因为sidno是一个连续的数值那么更具sidno找到sid只需要简单的做
                                                 //数组查找即可这里将node指针存入
  /**
    Hash that maps SID to SIDNO.  The keys in this array are of type
    rpl_sid.
  */
  HASH _sid_to_sidno;                           //因为sid是一个数据结构其核心为bytes关键值存储了16字节根据server_uuid
                                                //转换而来的无规律内存空间，需要使用hash查找表快速定位
  /**
    Array that maps numbers in the interval [0, get_max_sidno()-1] to
    SIDNOs, in order of increasing SID.

    @see Sid_map::get_sorted_sidno.
  */
  Prealloced_array<rpl_sidno, 8, true> _sorted;//额外的一个关于sidno的数组，具体作用未知

 struct Node
  {
    rpl_sidno sidno; //sid hash no
    rpl_sid sid; //sid
  };

| gtid_executed                    | 
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/**
    Array where the N'th element contains the head pointer to the
    intervals of SIDNO N+1.
  */
  Prealloced_array<Interval*, 8, true> m_intervals;//每个sidno 包含一个Interval 单项链表，由next指针连接 这就完成了比如分割GTID的问题
  /// Linked list of free intervals.
  Interval *free_intervals;  //空闲的interval连接在这个链表上
  /// Linked list of chunks.
  Interval_chunk *chunks; //全局的一个Interval 链表 所有的Interval空间都连接在上面

 /// The first GNO of this interval.
    rpl_gno start;
    /// The first GNO after this interval.
    rpl_gno end;
    /// Pointer to next interval in list.
    Interval *next;

/// The Sid_map used by this Gtid_state.
  mutable Sid_map *sid_map; //使用sid_map
  /**
    The set of GTIDs that existed in some previously purged binary log.
    This is always a subset of executed_gtids.
  */
  Gtid_set lost_gtids; //对应gtid_purged参数，这个参数一般由Mysql自动维护除非手动设置了gtid_purged参数
  /*
    The set of GTIDs that has been executed and
    stored into gtid_executed table.
  */
  Gtid_set executed_gtids; //对应gtid_executed参数，这个参数一般由Mysql主动维护
  /*
    The set of GTIDs that exists only in gtid_executed table, not in
    binlog files.
  */
  Gtid_set gtids_only_in_table;
//正常来讲对于主库这个集合始终为空因为主库不可能存在只在mysql.gtid_executed表而不再binlog中的gtid，但是从库则必须开启log_slave_updates和binlog才会达到这个效果，
//否则binlog不包含relay的Gtid的只能包含在mysql.gtid_executed表中，那么这种情况下Gtid_set gtids_only_in_table是始终存在的。具体后面还会解释。
  /* The previous GTIDs in the last binlog. */
  Gtid_set previous_gtids_logged;//包含上一个binlog已经执行的所有的在binlog的Gtid
  /// The set of GTIDs that are owned by some thread.
  Owned_gtids owned_gtids;//当前所有线程拥有的全部Gtid集合
  /// The SIDNO for this server.
  rpl_sidno server_sidno;//就是服务器server_uuid对应sid hash出来的sidno

 /// Growable array of hashes.
  Prealloced_array<HASH*, 8, true> sidno_to_hash;

 struct Node
  {
    /// GNO of the group.
    rpl_gno gno;
    /// Owner of the group.
    my_thread_id owner;
  };