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PostgreSQL 源码解读(125)- MVCC#9(vacuum-主流程)

原创 PostgreSQL 作者:husthxd 时间:2019-01-21 17:55:23 0 删除 编辑

本节简单介绍了PostgreSQL手工执行vacuum的主处理流程,主要分析了ExecVacuum函数的实现逻辑。

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, &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;

DONE!

四、参考资料

PG Source Code

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