本篇内容介绍了“PostgreSQL中vacuum主流程分析”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
Vacuum和Analyze命令选项
typedef enum VacuumOption
{
VACOPT_VACUUM = 1 << 0,
VACOPT_ANALYZE = 1 << 1,
VACOPT_VERBOSE = 1 << 2,
VACOPT_FREEZE = 1 << 3,
VACOPT_FULL = 1 << 4,
VACOPT_SKIP_LOCKED = 1 << 5,
VACOPT_SKIPTOAST = 1 << 6,
VACOPT_DISABLE_PAGE_SKIPPING = 1 << 7
} VacuumOption;VacuumStmt
存储vacuum命令的option&Relation链表
typedef struct VacuumStmt
{
NodeTag type;//Tag
//VacuumOption位标记
int options;
//VacuumRelation链表,如为NIL-->所有Relation.
List *rels;
} VacuumStmt;VacuumParams
vacuum命令参数
typedef struct VacuumParams
{
//最小freeze age,-1表示使用默认
int freeze_min_age;
//扫描整个table的freeze age
int freeze_table_age;
//最小的multixact freeze age,-1表示默认
int multixact_freeze_min_age;
//扫描全表的freeze age,-1表示默认
int multixact_freeze_table_age;
//是否强制wraparound?
bool is_wraparound;
//以毫秒为单位的最小执行阈值
int log_min_duration;
} VacuumParams;VacuumRelation
VACUUM/ANALYZE命令的目标表信息
typedef struct VacuumRelation
{
NodeTag type;
RangeVar *relation;
Oid oid;
List *va_cols;
} VacuumRelation;二、源码解读
ExecVacuum函数,手工执行VACUUM/ANALYZE命令时的主入口,vacuum()函数的包装器(wrapper).
void
ExecVacuum(VacuumStmt *vacstmt, bool isTopLevel)
{
VacuumParams params;
//验证&检查
Assert(vacstmt->options & (VACOPT_VACUUM | VACOPT_ANALYZE));
Assert((vacstmt->options & VACOPT_VACUUM) ||
!(vacstmt->options & (VACOPT_FULL | VACOPT_FREEZE)));
Assert(!(vacstmt->options & VACOPT_SKIPTOAST));
if (!(vacstmt->options & VACOPT_ANALYZE))
{
ListCell *lc;
foreach(lc, vacstmt->rels)
{
VacuumRelation *vrel = lfirst_node(VacuumRelation, lc);
if (vrel->va_cols != NIL)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("ANALYZE option must be specified when a column list is provided")));
}
}
if (vacstmt->options & VACOPT_FREEZE)
{
//指定VACOPT_FREEZE
params.freeze_min_age = 0;
params.freeze_table_age = 0;
params.multixact_freeze_min_age = 0;
params.multixact_freeze_table_age = 0;
}
else
{
params.freeze_min_age = -1;
params.freeze_table_age = -1;
params.multixact_freeze_min_age = -1;
params.multixact_freeze_table_age = -1;
}
//用户调用的vacuum永远不会是wraparound
params.is_wraparound = false;
//用户调用vacuum永远不会使用该参数
params.log_min_duration = -1;
//调用vacuum
vacuum(vacstmt->options, vacstmt->rels, ¶ms, NULL, isTopLevel);
}三、跟踪分析
测试脚本
17:19:28 (xdb@[local]:5432)testdb=# vacuum t1;启动gdb,设置断点
(gdb) b ExecVacuum
Breakpoint 1 at 0x6b99a1: file vacuum.c, line 92.
(gdb) c
Continuing.
Breakpoint 1, ExecVacuum (vacstmt=0x210e9c0, isTopLevel=true) at vacuum.c:92
92 Assert(vacstmt->options & (VACOPT_VACUUM | VACOPT_ANALYZE));
(gdb)输入参数
options = 1 —> VACOPT_VACUUM
(gdb) p *vacstmt
$1 = {type = T_VacuumStmt, options = 1, rels = 0x210e988}
(gdb)获取Relation相关信息
gdb) n
93 Assert((vacstmt->options & VACOPT_VACUUM) ||
(gdb)
95 Assert(!(vacstmt->options & VACOPT_SKIPTOAST));
(gdb)
100 if (!(vacstmt->options & VACOPT_ANALYZE))
(gdb)
104 foreach(lc, vacstmt->rels)
(gdb)
106 VacuumRelation *vrel = lfirst_node(VacuumRelation, lc);
(gdb)
108 if (vrel->va_cols != NIL)
(gdb) p *vrel
$3 = {type = T_VacuumRelation, relation = 0x210e8d0, oid = 0, va_cols = 0x0}
(gdb) p *vrel->relation
$4 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x210e8b0 "t1", inh = true,
relpersistence = 112 'p', alias = 0x0, location = 7}
(gdb)设置vacuum参数
(gdb) n
104 foreach(lc, vacstmt->rels)
(gdb)
119 if (vacstmt->options & VACOPT_FREEZE)
(gdb)
128 params.freeze_min_age = -1;
(gdb)
129 params.freeze_table_age = -1;
(gdb)
130 params.multixact_freeze_min_age = -1;
(gdb)
131 params.multixact_freeze_table_age = -1;
(gdb)
135 params.is_wraparound = false;
(gdb)
(gdb) n
138 params.log_min_duration = -1;
(gdb)调用vacuum
141 vacuum(vacstmt->options, vacstmt->rels, ¶ms, NULL, isTopLevel);
(gdb)
142 }
(gdb)
standard_ProcessUtility (pstmt=0x210ea80, queryString=0x210dec8 "vacuum t1;", context=PROCESS_UTILITY_TOPLEVEL, params=0x0,
queryEnv=0x0, dest=0x210ed70, completionTag=0x7fff1d69dea0 "") at utility.c:672
672 break;“PostgreSQL中vacuum主流程分析”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！
