PostgreSQL 原始碼解讀（108）- 後臺程式#1（PGPROC資料結構）

husthxd發表於2018-12-12
SQL原始碼資料結構

PostgreSQL使用程式模式，對於每一個客戶端會Fork一個後臺程式響應客戶端的請求。本節介紹了每個後臺程式在共享記憶體中都存在一個的資料結構：PGPROC。

一、資料結構

宏定義

/*
 * Note: MAX_BACKENDS is limited to 2^18-1 because that's the width reserved
 * for buffer references in buf_internals.h.  This limitation could be lifted
 * by using a 64bit state; but it's unlikely to be worthwhile as 2^18-1
 * backends exceed currently realistic configurations. Even if that limitation
 * were removed, we still could not a) exceed 2^23-1 because inval.c stores
 * the backend ID as a 3-byte signed integer, b) INT_MAX/4 because some places
 * compute 4*MaxBackends without any overflow check.  This is rechecked in the
 * relevant GUC check hooks and in RegisterBackgroundWorker().
 * 注意:MAX_BACKENDS限制為2^18-1,
 *   這是因為該值為buf_internals.h中定義的快取依賴的最大寬度.
 * 該限制可以透過使用64bit的狀態來提升,但它看起來並不值當.
 * 如果去掉該限制,我們仍然不能夠超過:
 *   a) 2^23-1,因為inval.c使用3個位元組的有符號整數儲存後臺程式ID
 *   b) INT_MAX/4 ,因為某些地方沒有任何的溢位檢查,直接計算4*MaxBackends的值.
 * 該值會在相關的GUC檢查鉤子和RegisterBackgroundWorker()函式中檢查.
 */
#define MAX_BACKENDS    0x3FFFF

/* shmqueue.c */
typedef struct SHM_QUEUE
{
    struct SHM_QUEUE *prev;
    struct SHM_QUEUE *next;
} SHM_QUEUE;

/*
 * An invalid pgprocno.  Must be larger than the maximum number of PGPROC
 * structures we could possibly have.  See comments for MAX_BACKENDS.
 * 無效的pg程式號.
 * 必須大於我們可能擁有的最大的PGPROC數目.
 * 詳細解釋見MAX_BACKENDS
 */
#define INVALID_PGPROCNO        PG_INT32_MAX

LWLock
lwlock.c外的程式碼不應直接操作這個結構的內容,但我們必須宣告該結構體以便將LWLocks合併到其他資料結構中。

/*
 * Code outside of lwlock.c should not manipulate the contents of this
 * structure directly, but we have to declare it here to allow LWLocks to be
 * incorporated into other data structures.
 * lwlock.c外的程式碼不應直接操作這個結構的內容,
 *   但我們必須宣告該結構體以便將LWLocks合併到其他資料結構中。
 */
typedef struct LWLock
{
    uint16      tranche;        /* tranche ID */
    //獨佔/非獨佔locker的狀態
    pg_atomic_uint32 state;     /* state of exclusive/nonexclusive lockers */
    //正在等待的PGPROCs連結串列
    proclist_head waiters;      /* list of waiting PGPROCs */
#ifdef LOCK_DEBUG//用於DEBUG
    //waiters的數量
    pg_atomic_uint32 nwaiters;  /* number of waiters */
    //鎖的最後獨佔者
    struct PGPROC *owner;       /* last exclusive owner of the lock */
#endif
} LWLock;

PGPROC
每個後臺程式在共享記憶體中都有一個PGPROC結構體.
全域性上也存在未使用的PGPROC結構體連結串列,用於重用以便為新的後臺程式進行分配.
該資料結構的作用是:

PostgreSQL backend processes can't see each other's memory directly, nor can the postmaster see into PostgreSQL backend process memory. Yet they need some way to communicate and co-ordinate, and the postmaster needs a way to keep track of them.

簡單來說作用是為了程式間協同和通訊以及postmaster的跟蹤.


/*
 * Each backend has a PGPROC struct in shared memory.  There is also a list of
 * currently-unused PGPROC structs that will be reallocated to new backends.
 * 每個後臺程式在共享記憶體中都有一個PGPROC結構體.
 * 存在未使用的PGPROC結構體連結串列,用於為新的後臺程式重新進行分配.
 * 
 * links: list link for any list the PGPROC is in.  When waiting for a lock,
 * the PGPROC is linked into that lock's waitProcs queue.  A recycled PGPROC
 * is linked into ProcGlobal's freeProcs list.
 * links: PGPROC所在的連結串列的連結.
 *   在等待鎖時,PGPROC連結到該鎖的waiProc佇列中.
 * 回收的PGPROC連結到ProcGlobal的freeProcs連結串列中.
 *
 * Note: twophase.c also sets up a dummy PGPROC struct for each currently
 * prepared transaction.  These PGPROCs appear in the ProcArray data structure
 * so that the prepared transactions appear to be still running and are
 * correctly shown as holding locks.  A prepared transaction PGPROC can be
 * distinguished from a real one at need by the fact that it has pid == 0.
 * The semaphore and lock-activity fields in a prepared-xact PGPROC are unused,
 * but its myProcLocks[] lists are valid.
 * 注意:twophase.c也會為每一個當前已準備妥當的事務配置一個虛擬的PGPROC結構.
 * 這些PGPROCs在陣列ProcArray資料結構中出現,以便已準備的事務看起來仍在執行,
 *   並正確的顯示為持有鎖.
 * 已準備妥當的事務PGPROC與一個真正的PGPROC事實上的區別是pid == 0.
 * 在prepared-xact PGPROC中的訊號量和活動鎖域欄位沒有使用,但myProcLocks[]連結串列是有效的.
 */
struct PGPROC
{
    /* proc->links MUST BE FIRST IN STRUCT (see ProcSleep,ProcWakeup,etc) */
    //proc->links必須是結構體的第一個域(參考ProcSleep,ProcWakeup...等)
    //如程式在連結串列中,這是連結串列的連結
    SHM_QUEUE   links;          /* list link if process is in a list */
    //持有該PGPROC的procglobal連結串列陣列
    PGPROC    **procgloballist; /* procglobal list that owns this PGPROC */
    //可以休眠的訊號量
    PGSemaphore sem;            /* ONE semaphore to sleep on */
    //狀態為:STATUS_WAITING, STATUS_OK or STATUS_ERROR
    int         waitStatus;     /* STATUS_WAITING, STATUS_OK or STATUS_ERROR */
    //程式通用的latch
    Latch       procLatch;      /* generic latch for process */
    //執行中的程式正在執行的最高層的事務本地ID,如無執行則為InvalidLocalTransactionId
    LocalTransactionId lxid;    /* local id of top-level transaction currently
                                 * being executed by this proc, if running;
                                 * else InvalidLocalTransactionId */
    //後臺程式的ID,如為虛擬事務則為0
    int         pid;            /* Backend's process ID; 0 if prepared xact */
    int         pgprocno;

    /* These fields are zero while a backend is still starting up: */
    //------------ 這些域在程式正在啟動時為0
    //已分配的後臺程式的backend ID
    BackendId   backendId;      /* This backend's backend ID (if assigned) */
    //該程式使用的資料庫ID
    Oid         databaseId;     /* OID of database this backend is using */
    //使用該程式的角色ID
    Oid         roleId;         /* OID of role using this backend */
    //該程式使用的臨時schema OID
    Oid         tempNamespaceId;    /* OID of temp schema this backend is
                                     * using */
    //如後臺程式,則為T
    bool        isBackgroundWorker; /* true if background worker. */

    /*
     * While in hot standby mode, shows that a conflict signal has been sent
     * for the current transaction. Set/cleared while holding ProcArrayLock,
     * though not required. Accessed without lock, if needed.
     * 如在hot standby模式,顯示已為當前事務傳送衝突訊號.
     * 儘管不需要,設定/清除持有的ProcArrayLock.
     * 如需要,則在沒有持有鎖的情況下訪問.
     */
    bool        recoveryConflictPending;

    /* Info about LWLock the process is currently waiting for, if any. */
    //-------------- 程式正在等待的LWLock相關資訊
    //等待LW lock,為T
    bool        lwWaiting;      /* true if waiting for an LW lock */
    //正在等的LWLock鎖模式
    uint8       lwWaitMode;     /* lwlock mode being waited for */
    //等待連結串列中的位置
    proclist_node lwWaitLink;   /* position in LW lock wait list */

    /* Support for condition variables. */
    //-------------- 支援條件變數
    //CV等待連結串列中的位置
    proclist_node cvWaitLink;   /* position in CV wait list */

    /* Info about lock the process is currently waiting for, if any. */
    //-------------- 程式正在等待的鎖資訊
    /* waitLock and waitProcLock are NULL if not currently waiting. */
    //如沒有在等待,則waitLock和waitProcLock為NULL
    //休眠...等待的鎖物件
    LOCK       *waitLock;       /* Lock object we're sleeping on ... */
    //等待鎖的每個持鎖人資訊
    PROCLOCK   *waitProcLock;   /* Per-holder info for awaited lock */
    //等待的所型別
    LOCKMODE    waitLockMode;   /* type of lock we're waiting for */
    //該程式已持有鎖的型別位掩碼
    LOCKMASK    heldLocks;      /* bitmask for lock types already held on this
                                 * lock object by this backend */

    /*
     * Info to allow us to wait for synchronous replication, if needed.
     * waitLSN is InvalidXLogRecPtr if not waiting; set only by user backend.
     * syncRepState must not be touched except by owning process or WALSender.
     * syncRepLinks used only while holding SyncRepLock.
     * 允許我們等待同步複製的相關資訊.
     * 如無需等待,則waitLSN為InvalidXLogRecPtr;僅允許由使用者後臺設定。
     * 除非擁有process或WALSender，否則不能修改syncRepState。
     * 僅在持有SyncRepLock時使用的syncrepink。
     */
    //--------------------- 
    //等待該LSN或者更高的LSN
    XLogRecPtr  waitLSN;        /* waiting for this LSN or higher */
    //同步複製的等待狀態
    int         syncRepState;   /* wait state for sync rep */
    //如程式處於syncrep佇列中,則該值儲存連結串列連結
    SHM_QUEUE   syncRepLinks;   /* list link if process is in syncrep queue */

    /*
     * All PROCLOCK objects for locks held or awaited by this backend are
     * linked into one of these lists, according to the partition number of
     * their lock.
     * 該後臺程式持有或等待的鎖相關的所有PROCLOCK物件連結在這些連結串列的末尾,
     *   根據棣屬於這些鎖的分割槽號進行區分.
     */
    SHM_QUEUE   myProcLocks[NUM_LOCK_PARTITIONS];
    //子事務的XIDs
    struct XidCache subxids;    /* cache for subtransaction XIDs */

    /* Support for group XID clearing. */
    /* true, if member of ProcArray group waiting for XID clear */
    //支援XID分組清除
    //如屬於等待XID清理的ProcArray組,則為T
    bool        procArrayGroupMember;
    /* next ProcArray group member waiting for XID clear */
    //等待XID清理的下一個ProcArray組編號
    pg_atomic_uint32 procArrayGroupNext;

    /*
     * latest transaction id among the transaction's main XID and
     * subtransactions
     * 在事務主XID和子事務之間的最後的事務ID
     */
    TransactionId procArrayGroupMemberXid;
    //程式的等待資訊
    uint32      wait_event_info;    /* proc's wait information */

    /* Support for group transaction status update. */
    //--------------- 支援組事務狀態更新
    //clog組成員,則為T
    bool        clogGroupMember;    /* true, if member of clog group */
    //下一個clog組成員
    pg_atomic_uint32 clogGroupNext; /* next clog group member */
    //clog組成員事務ID
    TransactionId clogGroupMemberXid;   /* transaction id of clog group member */
    //clog組成員的事務狀態
    XidStatus   clogGroupMemberXidStatus;   /* transaction status of clog
                                             * group member */
    //屬於clog組成員的事務ID的clog page
    int         clogGroupMemberPage;    /* clog page corresponding to
                                         * transaction id of clog group member */
    //clog組成員已提交記錄的WAL位置
    XLogRecPtr  clogGroupMemberLsn; /* WAL location of commit record for clog
                                     * group member */

    /* Per-backend LWLock.  Protects fields below (but not group fields). */
    //每一個後臺程式一個LWLock.保護下面的域欄位(非組欄位)
    LWLock      backendLock;

    /* Lock manager data, recording fast-path locks taken by this backend. */
    //---------- 鎖管理資料,記錄該後臺程式以最快路徑獲得的鎖
    //每一個fast-path slot的鎖模式
    uint64      fpLockBits;     /* lock modes held for each fast-path slot */
    //rel oids的slots
    Oid         fpRelId[FP_LOCK_SLOTS_PER_BACKEND]; /* slots for rel oids */
    //是否持有fast-path VXID鎖
    bool        fpVXIDLock;     /* are we holding a fast-path VXID lock? */
    //fast-path VXID鎖的lxid
    LocalTransactionId fpLocalTransactionId;    /* lxid for fast-path VXID
                                                 * lock */

    /*
     * Support for lock groups.  Use LockHashPartitionLockByProc on the group
     * leader to get the LWLock protecting these fields.
     */
    //--------- 支援鎖組.
    //          在組leader中使用LockHashPartitionLockByProc獲取LWLock保護這些域
    //鎖組的leader,如果"我"是其中一員
    PGPROC     *lockGroupLeader;    /* lock group leader, if I'm a member */
    //如果"我"是leader,這是成員的連結串列
    dlist_head  lockGroupMembers;   /* list of members, if I'm a leader */
    //成員連線,如果"我"是其中一員
    dlist_node  lockGroupLink;  /* my member link, if I'm a member */
};

MyProc
每個程式都有一個全域性變數:MyProc

extern PGDLLIMPORT PGPROC *MyProc;
extern PGDLLIMPORT struct PGXACT *MyPgXact;

二、原始碼解讀

N/A

三、跟蹤分析

啟動兩個Session,執行同樣的SQL語句:

insert into t_wal_partition(c1,c2,c3) VALUES(0,'HASH0','HAHS0');

Session 1
啟動gdb,開啟跟蹤

(gdb) b XLogInsertRecord
Breakpoint 1 at 0x54d122: file xlog.c, line 970.
(gdb) c
Continuing.

Breakpoint 1, XLogInsertRecord (rdata=0xf9cc70 <hdr_rdt>, fpw_lsn=0, flags=1 '\001') at xlog.c:970
970     XLogCtlInsert *Insert = &XLogCtl->Insert;

檢視記憶體中的資料結構

(gdb) p *MyProc
$3 = {links = {prev = 0x0, next = 0x0}, procgloballist = 0x7fa79c087c98, sem = 0x7fa779fc81b8, waitStatus = 0, procLatch = {
    is_set = 0, is_shared = true, owner_pid = 1398}, lxid = 3, pid = 1398, pgprocno = 99, backendId = 3, 
  databaseId = 16402, roleId = 10, tempNamespaceId = 0, isBackgroundWorker = false, recoveryConflictPending = false, 
  lwWaiting = false, lwWaitMode = 0 '\000', lwWaitLink = {next = 0, prev = 0}, cvWaitLink = {next = 0, prev = 0}, 
  waitLock = 0x0, waitProcLock = 0x0, waitLockMode = 0, heldLocks = 0, waitLSN = 0, syncRepState = 0, syncRepLinks = {
    prev = 0x0, next = 0x0}, myProcLocks = {{prev = 0x7fa79c09c588, next = 0x7fa79c09c588}, {prev = 0x7fa79c09c598, 
      next = 0x7fa79c09c598}, {prev = 0x7fa79c09c5a8, next = 0x7fa79c09c5a8}, {prev = 0x7fa79c09c5b8, 
      next = 0x7fa79c09c5b8}, {prev = 0x7fa79c09c5c8, next = 0x7fa79c09c5c8}, {prev = 0x7fa79c09c5d8, 
      next = 0x7fa79c09c5d8}, {prev = 0x7fa79c09c5e8, next = 0x7fa79c09c5e8}, {prev = 0x7fa79c09c5f8, 
      next = 0x7fa79c09c5f8}, {prev = 0x7fa79c09c608, next = 0x7fa79c09c608}, {prev = 0x7fa79c09c618, 
      next = 0x7fa79c09c618}, {prev = 0x7fa79c09c628, next = 0x7fa79c09c628}, {prev = 0x7fa79c09c638, 
      next = 0x7fa79c09c638}, {prev = 0x7fa79c09c648, next = 0x7fa79c09c648}, {prev = 0x7fa79c09c658, 
      next = 0x7fa79c09c658}, {prev = 0x7fa79c09c668, next = 0x7fa79c09c668}, {prev = 0x7fa79be25e70, 
      next = 0x7fa79be25e70}}, subxids = {xids = {0 <repeats 64 times>}}, procArrayGroupMember = false, 
  procArrayGroupNext = {value = 2147483647}, procArrayGroupMemberXid = 0, wait_event_info = 0, clogGroupMember = false, 
  clogGroupNext = {value = 2147483647}, clogGroupMemberXid = 0, clogGroupMemberXidStatus = 0, clogGroupMemberPage = -1, 
  clogGroupMemberLsn = 0, backendLock = {tranche = 58, state = {value = 536870912}, waiters = {head = 2147483647, 
      tail = 2147483647}}, fpLockBits = 196027139227648, fpRelId = {0, 0, 0, 0, 0, 2679, 2610, 2680, 2611, 17043, 17040, 
    17037, 17034, 17031, 17028, 17025}, fpVXIDLock = true, fpLocalTransactionId = 3, lockGroupLeader = 0x0, 
  lockGroupMembers = {head = {prev = 0x7fa79c09c820, next = 0x7fa79c09c820}}, lockGroupLink = {prev = 0x0, next = 0x0}}

注意:lwWaiting值為false,表示沒有在等待LW Lock

Session 2
啟動gdb,開啟跟蹤

(gdb) b heap_insert
Breakpoint 2 at 0x4df4d1: file heapam.c, line 2449.
(gdb) c
Continuing.
^C
Program received signal SIGINT, Interrupt.
0x00007fa7a7ee7a0b in futex_abstimed_wait (cancel=true, private=<optimized out>, abstime=0x0, expected=0, 
    futex=0x7fa779fc8138) at ../nptl/sysdeps/unix/sysv/linux/sem_waitcommon.c:43
43        err = lll_futex_wait (futex, expected, private);

暫無法進入heap_insert
檢視記憶體中的資料結構

(gdb) p *MyProc
$36 = {links = {prev = 0x0, next = 0x0}, procgloballist = 0x7fa79c087c98, sem = 0x7fa779fc8138, waitStatus = 0, 
  procLatch = {is_set = 1, is_shared = true, owner_pid = 1449}, lxid = 13, pid = 1449, pgprocno = 98, backendId = 4, 
  databaseId = 16402, roleId = 10, tempNamespaceId = 0, isBackgroundWorker = false, recoveryConflictPending = false, 
  lwWaiting = true, lwWaitMode = 0 '\000', lwWaitLink = {next = 114, prev = 2147483647}, cvWaitLink = {next = 0, prev = 0}, 
  waitLock = 0x0, waitProcLock = 0x0, waitLockMode = 0, heldLocks = 0, waitLSN = 0, syncRepState = 0, syncRepLinks = {
    prev = 0x0, next = 0x0}, myProcLocks = {{prev = 0x7fa79c09c238, next = 0x7fa79c09c238}, {prev = 0x7fa79c09c248, 
      next = 0x7fa79c09c248}, {prev = 0x7fa79c09c258, next = 0x7fa79c09c258}, {prev = 0x7fa79c09c268, 
      next = 0x7fa79c09c268}, {prev = 0x7fa79c09c278, next = 0x7fa79c09c278}, {prev = 0x7fa79c09c288, 
      next = 0x7fa79c09c288}, {prev = 0x7fa79c09c298, next = 0x7fa79c09c298}, {prev = 0x7fa79c09c2a8, 
      next = 0x7fa79c09c2a8}, {prev = 0x7fa79c09c2b8, next = 0x7fa79c09c2b8}, {prev = 0x7fa79c09c2c8, 
      next = 0x7fa79c09c2c8}, {prev = 0x7fa79c09c2d8, next = 0x7fa79c09c2d8}, {prev = 0x7fa79c09c2e8, 
      next = 0x7fa79c09c2e8}, {prev = 0x7fa79c09c2f8, next = 0x7fa79c09c2f8}, {prev = 0x7fa79c09c308, 
      next = 0x7fa79c09c308}, {prev = 0x7fa79be21870, next = 0x7fa79be21870}, {prev = 0x7fa79c09c328, 
      next = 0x7fa79c09c328}}, subxids = {xids = {0 <repeats 64 times>}}, procArrayGroupMember = false, 
  procArrayGroupNext = {value = 2147483647}, procArrayGroupMemberXid = 0, wait_event_info = 16777270, 
  clogGroupMember = false, clogGroupNext = {value = 2147483647}, clogGroupMemberXid = 0, clogGroupMemberXidStatus = 0, 
  clogGroupMemberPage = -1, clogGroupMemberLsn = 0, backendLock = {tranche = 58, state = {value = 536870912}, waiters = {
      head = 2147483647, tail = 2147483647}}, fpLockBits = 196027139227648, fpRelId = {0, 0, 0, 0, 0, 2655, 2603, 2680, 
    2611, 17043, 17040, 17037, 17034, 17031, 17028, 17025}, fpVXIDLock = true, fpLocalTransactionId = 13, 
  lockGroupLeader = 0x0, lockGroupMembers = {head = {prev = 0x7fa79c09c4d0, next = 0x7fa79c09c4d0}}, lockGroupLink = {
    prev = 0x0, next = 0x0}}

注意:
lwWaiting值為true,正在等待Session 1的LWLock.
lwWaitLink = {next = 114, prev = 2147483647},其中next = 114,這裡的114是指全域性變數ProcGlobal(型別為PROC_HDR)->allProcs陣列下標為114的ITEM.

(gdb) p ProcGlobal->allProcs[114]
$41 = {links = {prev = 0x0, next = 0x0}, procgloballist = 0x0, sem = 0x7fa779fc8938, waitStatus = 0, procLatch = {
    is_set = 0, is_shared = true, owner_pid = 1351}, lxid = 0, pid = 1351, pgprocno = 114, backendId = -1, databaseId = 0, 
  roleId = 0, tempNamespaceId = 0, isBackgroundWorker = false, recoveryConflictPending = false, lwWaiting = true, 
  lwWaitMode = 1 '\001', lwWaitLink = {next = 2147483647, prev = 98}, cvWaitLink = {next = 0, prev = 0}, waitLock = 0x0, 
  waitProcLock = 0x0, waitLockMode = 0, heldLocks = 0, waitLSN = 0, syncRepState = 0, syncRepLinks = {prev = 0x0, 
    next = 0x0}, myProcLocks = {{prev = 0x7fa79c09f738, next = 0x7fa79c09f738}, {prev = 0x7fa79c09f748, 
      next = 0x7fa79c09f748}, {prev = 0x7fa79c09f758, next = 0x7fa79c09f758}, {prev = 0x7fa79c09f768, 
      next = 0x7fa79c09f768}, {prev = 0x7fa79c09f778, next = 0x7fa79c09f778}, {prev = 0x7fa79c09f788, 
      next = 0x7fa79c09f788}, {prev = 0x7fa79c09f798, next = 0x7fa79c09f798}, {prev = 0x7fa79c09f7a8, 
      next = 0x7fa79c09f7a8}, {prev = 0x7fa79c09f7b8, next = 0x7fa79c09f7b8}, {prev = 0x7fa79c09f7c8, 
      next = 0x7fa79c09f7c8}, {prev = 0x7fa79c09f7d8, next = 0x7fa79c09f7d8}, {prev = 0x7fa79c09f7e8, 
      next = 0x7fa79c09f7e8}, {prev = 0x7fa79c09f7f8, next = 0x7fa79c09f7f8}, {prev = 0x7fa79c09f808, 
      next = 0x7fa79c09f808}, {prev = 0x7fa79c09f818, next = 0x7fa79c09f818}, {prev = 0x7fa79c09f828, 
      next = 0x7fa79c09f828}}, subxids = {xids = {0 <repeats 64 times>}}, procArrayGroupMember = false, 
  procArrayGroupNext = {value = 0}, procArrayGroupMemberXid = 0, wait_event_info = 16777270, clogGroupMember = false, 
  clogGroupNext = {value = 0}, clogGroupMemberXid = 0, clogGroupMemberXidStatus = 0, clogGroupMemberPage = 0, 
  clogGroupMemberLsn = 0, backendLock = {tranche = 58, state = {value = 536870912}, waiters = {head = 2147483647, 
      tail = 2147483647}}, fpLockBits = 0, fpRelId = {0 <repeats 16 times>}, fpVXIDLock = false, fpLocalTransactionId = 0, 
  lockGroupLeader = 0x0, lockGroupMembers = {head = {prev = 0x7fa79c09f9d0, next = 0x7fa79c09f9d0}}, lockGroupLink = {
    prev = 0x0, next = 0x0}}

ProcGlobal下節再行介紹

四、參考資料

What is the role of struct 'PGPROC' in PostgreSQL?

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374781/，如需轉載，請註明出處，否則將追究法律責任。

相關文章