PostgreSQL中vacuum主流程分析
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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)
*/
void
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, ¶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;
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