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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，接下来就让丸趣 TV 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
/* ----------------------
* Vacuum and Analyze Statements
* Vacuum 和 Analyze 命令选项
*
* Even though these are nominally two statements, it s convenient to use
* just one node type for both. Note that at least one of VACOPT_VACUUM
* and VACOPT_ANALYZE must be set in options.
* 虽然在这里有两种不同的语句, 但只需要使用统一的 Node 类型即可.
* 注意至少 VACOPT_VACUUM/VACOPT_ANALYZE 在选项中设置.
* ----------------------
*/
typedef enum VacuumOption
VACOPT_VACUUM = 1 0, /* do VACUUM */
VACOPT_ANALYZE = 1 1, /* do ANALYZE */
VACOPT_VERBOSE = 1 2, /* print progress info */
VACOPT_FREEZE = 1 3, /* FREEZE option */
VACOPT_FULL = 1 4, /* FULL (non-concurrent) vacuum */
VACOPT_SKIP_LOCKED = 1 5, /* skip if cannot get lock */
VACOPT_SKIPTOAST = 1 6, /* don t process the TOAST table, if any */
VACOPT_DISABLE_PAGE_SKIPPING = 1 7 /* don t skip any pages */
} VacuumOption;VacuumStmt
存储 vacuum 命令的 option Relation 链表
typedef struct VacuumStmt
NodeTag type;//Tag
//VacuumOption 位标记
int options; /* OR of VacuumOption flags */
//VacuumRelation 链表, 如为 NIL-- 所有 Relation.
List *rels; /* list of VacuumRelation, or NIL for all */
} VacuumStmt;VacuumParams
vacuum 命令参数
/*
* Parameters customizing behavior of VACUUM and ANALYZE.
* 客户端调用 VACUUM/ANALYZE 时的定制化参数
*/
typedef struct VacuumParams
// 最小 freeze age,- 1 表示使用默认
int freeze_min_age; /* min freeze age, -1 to use default */
// 扫描整个 table 的 freeze age
int freeze_table_age; /* age at which to scan whole table */
// 最小的 multixact freeze age,- 1 表示默认
int multixact_freeze_min_age; /* min multixact freeze age, -1 to
* use default */
// 扫描全表的 freeze age,- 1 表示默认
int multixact_freeze_table_age; /* multixact age at which to scan
* whole table */
// 是否强制 wraparound?
bool is_wraparound; /* force a for-wraparound vacuum */
// 以毫秒为单位的最小执行阈值
int log_min_duration; /* minimum execution threshold in ms at
* which verbose logs are activated, -1
* to use default */
} VacuumParams;VacuumRelation
VACUUM/ANALYZE 命令的目标表信息
/*
* Info about a single target table of VACUUM/ANALYZE.
* VACUUM/ANALYZE 命令的目标表信息.
*
* If the OID field is set, it always identifies the table to process.
* Then the relation field can be NULL; if it isn t, it s used only to report
* failure to open/lock the relation.
* 如设置了 OID 字段, 该值通常是将要处理的数据表.
* 那么关系字段可以为空; 如果不是，则仅用于报告未能打开 / 锁定关系。 */
typedef struct VacuumRelation
NodeTag type;
RangeVar *relation; /* table name to process, or NULL */
Oid oid; /* table s OID; InvalidOid if not looked up */
List *va_cols; /* list of column names, or NIL for all */
} 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).
/*
* Primary entry point for manual VACUUM and ANALYZE commands
* 手工执行 VACUUM/ANALYZE 命令时的主入口
*
* This is mainly a preparation wrapper for the real operations that will
* happen in vacuum().
* 这是 vacuum() 函数的包装器 (wrapper)
*/
ExecVacuum(VacuumStmt *vacstmt, bool isTopLevel)
VacuumParams params;
/* sanity checks on options */
// 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));
/*
* Make sure VACOPT_ANALYZE is specified if any column lists are present.
* 如出现字段列表, 则确保指定了 VACOPT_ANALYZE 选项
*/
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)));
}
}
/*
* All freeze ages are zero if the FREEZE option is given; otherwise pass
* them as -1 which means to use the default values.
* 如指定了 FREEZE 选项则设置所有 freeze ages 为 0.
* 否则的话, 传递 -1(即使用默认值).
*/
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;
}
/* user-invoked vacuum is never for wraparound */
// 用户调用的 vacuum 永远不会是 wraparound
params.is_wraparound = false;
/* user-invoked vacuum never uses this parameter */
// 用户调用 vacuum 永远不会使用该参数
params.log_min_duration = -1;
/* Now go through the common routine */
// 调用 vacuum
vacuum(vacstmt- options, vacstmt- rels, params, 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, params, 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丸趣 TV 网站，丸趣 TV 小编将为大家输出更多高质量的实用文章！
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