本篇内容介绍了“PostgreSQL中PGPROC数据结构分析”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！
一、数据结构
宏定义
#define MAX_BACKENDS 0x3FFFF
typedef struct SHM_QUEUE
{
struct SHM_QUEUE *prev;
struct SHM_QUEUE *next;
} SHM_QUEUE;
#define INVALID_PGPROCNO PG_INT32_MAXLWLock
lwlock.c外的代码不应直接操作这个结构的内容,但我们必须声明该结构体以便将LWLocks合并到其他数据结构中。
typedef struct LWLock
{
uint16 tranche;
//独占/非独占locker的状态
pg_atomic_uint32 state;
//正在等待的PGPROCs链表
proclist_head waiters;
#ifdef LOCK_DEBUG//用于DEBUG
//waiters的数量
pg_atomic_uint32 nwaiters;
//锁的最后独占者
struct PGPROC *owner;
#endif
} LWLock;PGPROC
每个后台进程在共享内存中都有一个PGPROC结构体.
全局上也存在未使用的PGPROC结构体链表,用于重用以便为新的后台进程进行分配.
该数据结构的作用是:
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.
简单来说作用是为了进程间协同和通讯以及postmaster的跟踪.
struct PGPROC
{
//proc->links必须是结构体的第一个域(参考ProcSleep,ProcWakeup...等)
//如进程在链表中,这是链表的链接
SHM_QUEUE links;
//持有该PGPROC的procglobal链表数组
PGPROC **procgloballist;
//可以休眠的信号量
PGSemaphore sem;
//状态为:STATUS_WAITING, STATUS_OK or STATUS_ERROR
int waitStatus;
//进程通用的latch
Latch procLatch;
//运行中的进程正在执行的最高层的事务本地ID,如无运行则为InvalidLocalTransactionId
LocalTransactionId lxid;
//后台进程的ID,如为虚拟事务则为0
int pid;
int pgprocno;
//------------ 这些域在进程正在启动时为0
//已分配的后台进程的backend ID
BackendId backendId;
//该进程使用的数据库ID
Oid databaseId;
//使用该进程的角色ID
Oid roleId;
//该进程使用的临时schema OID
Oid tempNamespaceId;
//如后台进程,则为T
bool isBackgroundWorker;
bool recoveryConflictPending;
//-------------- 进程正在等待的LWLock相关信息
//等待LW lock,为T
bool lwWaiting;
//正在等的LWLock锁模式
uint8 lwWaitMode;
//等待链表中的位置
proclist_node lwWaitLink;
//-------------- 支持条件变量
//CV等待链表中的位置
proclist_node cvWaitLink;
//-------------- 进程正在等待的锁信息
//如没有在等待,则waitLock和waitProcLock为NULL
//休眠...等待的锁对象
LOCK *waitLock;
//等待锁的每个持锁人信息
PROCLOCK *waitProcLock;
//等待的所类型
LOCKMODE waitLockMode;
//该进程已持有锁的类型位掩码
LOCKMASK heldLocks;
//---------------------
//等待该LSN或者更高的LSN
XLogRecPtr waitLSN;
//同步复制的等待状态
int syncRepState;
//如进程处于syncrep队列中,则该值保存链表链接
SHM_QUEUE syncRepLinks;
SHM_QUEUE myProcLocks[NUM_LOCK_PARTITIONS];
//子事务的XIDs
struct XidCache subxids;
//支持XID分组清除
//如属于等待XID清理的ProcArray组,则为T
bool procArrayGroupMember;
//等待XID清理的下一个ProcArray组编号
pg_atomic_uint32 procArrayGroupNext;
TransactionId procArrayGroupMemberXid;
//进程的等待信息
uint32 wait_event_info;
//--------------- 支持组事务状态更新
//clog组成员,则为T
bool clogGroupMember;
//下一个clog组成员
pg_atomic_uint32 clogGroupNext;
//clog组成员事务ID
TransactionId clogGroupMemberXid;
//clog组成员的事务状态
XidStatus clogGroupMemberXidStatus;
//属于clog组成员的事务ID的clog page
int clogGroupMemberPage;
//clog组成员已提交记录的WAL位置
XLogRecPtr clogGroupMemberLsn;
//每一个后台进程一个LWLock.保护下面的域字段(非组字段)
LWLock backendLock;
//---------- 锁管理数据,记录该后台进程以最快路径获得的锁
//每一个fast-path slot的锁模式
uint64 fpLockBits;
//rel oids的slots
Oid fpRelId[FP_LOCK_SLOTS_PER_BACKEND];
//是否持有fast-path VXID锁
bool fpVXIDLock;
//fast-path VXID锁的lxid
LocalTransactionId fpLocalTransactionId;
//--------- 支持锁组.
// 在组leader中使用LockHashPartitionLockByProc获取LWLock保护这些域
//锁组的leader,如果"我"是其中一员
PGPROC *lockGroupLeader;
//如果"我"是leader,这是成员的链表
dlist_head lockGroupMembers;
//成员连接,如果"我"是其中一员
dlist_node lockGroupLink;
};MyProc
每个进程都有一个全局变量:MyProc
extern PGDLLIMPORT PGPROC *MyProc;
extern PGDLLIMPORT struct PGXACT *MyPgXact;二、源码解读
N/A
三、跟踪分析
启动两个Session,执行同样的SQL语句:
insert into t_wal_partition(c1,c2,c3) VALUES(0,'HASH0','HAHS0');Session 1
启动gdb,开启跟踪
(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;查看内存中的数据结构
(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值为false,表示没有在等待LW Lock
Session 2
启动gdb,开启跟踪
(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);暂无法进入heap_insert
查看内存中的数据结构
(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值为true,正在等待Session 1的LWLock.
lwWaitLink = {next = 114, prev = 2147483647},其中next = 114,这里的114是指全局变量ProcGlobal(类型为PROC_HDR)->allProcs数组下标为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}}“PostgreSQL中PGPROC数据结构分析”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站，小编将为大家输出更多高质量的实用文章！
