postgreSQL 12-2 vacuum-主流程
記錄自學postgreSQL原始碼的過程， 非常感謝大神的分享
大量借鑑了大神的部落格內容，拜謝。
本人屬於初學者，理解能力，程式碼閱讀能力也有限，如果由錯誤的地方請多多諒解，歡迎討論。
原始碼如下
/*
* Primary entry point for manual VACUUM and ANALYZE commands
* 手工執行VACUUM/ANALYZE命令時的主入口
*
* This is mainly a preparation wrapper for the real operations that will
* happen in vacuum().
* 這是vacuum()函式的包裝器(wrapper)
*/
void
ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
{
VacuumParams params;
bool verbose = false;
bool skip_locked = false;
bool analyze = false;
bool freeze = false;
bool full = false;
bool disable_page_skipping = false;
ListCell *lc;
/* Set default value */
//@lguan
//設定預設值
params.index_cleanup = VACOPT_TERNARY_DEFAULT;
params.truncate = VACOPT_TERNARY_DEFAULT;
/* Parse options list */
//解析選項鍊表
foreach(lc, vacstmt->options)
{
DefElem *opt = (DefElem *) lfirst(lc);
/* Parse common options for VACUUM and ANALYZE */
//解析VACUUM和ANALYZE的常用選項
if (strcmp(opt->defname, "verbose") == 0)
verbose = defGetBoolean(opt);
else if (strcmp(opt->defname, "skip_locked") == 0)
skip_locked = defGetBoolean(opt);
else if (!vacstmt->is_vacuumcmd)
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("unrecognized ANALYZE option \"%s\"", opt->defname),
parser_errposition(pstate, opt->location)));
/* Parse options available on VACUUM */
//解析VACUUM的可用引數
else if (strcmp(opt->defname, "analyze") == 0)
analyze = defGetBoolean(opt);
else if (strcmp(opt->defname, "freeze") == 0)
freeze = defGetBoolean(opt);
else if (strcmp(opt->defname, "full") == 0)
full = defGetBoolean(opt);
else if (strcmp(opt->defname, "disable_page_skipping") == 0)
disable_page_skipping = defGetBoolean(opt);
else if (strcmp(opt->defname, "index_cleanup") == 0)
params.index_cleanup = get_vacopt_ternary_value(opt);
else if (strcmp(opt->defname, "truncate") == 0)
params.truncate = get_vacopt_ternary_value(opt);
else
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("unrecognized VACUUM option \"%s\"", opt->defname),
parser_errposition(pstate, opt->location)));
}
/* Set vacuum options */
//設定vacuum選項
params.options =
(vacstmt->is_vacuumcmd ? VACOPT_VACUUM : VACOPT_ANALYZE) |
(verbose ? VACOPT_VERBOSE : 0) |
(skip_locked ? VACOPT_SKIP_LOCKED : 0) |
(analyze ? VACOPT_ANALYZE : 0) |
(freeze ? VACOPT_FREEZE : 0) |
(full ? VACOPT_FULL : 0) |
(disable_page_skipping ? VACOPT_DISABLE_PAGE_SKIPPING : 0);
/* sanity checks on options */
//安全測試
Assert(params.options & (VACOPT_VACUUM | VACOPT_ANALYZE));
Assert((params.options & VACOPT_VACUUM) ||
!(params.options & (VACOPT_FULL | VACOPT_FREEZE)));
Assert(!(params.options & VACOPT_SKIPTOAST));
/*
* Make sure VACOPT_ANALYZE is specified if any column lists are present.
* 如出現欄位列表,則確保指定了VACOPT_ANALYZE選項
* @lguan
* 當清理選項指定了列欄位，那麼要確保VACOPT_ANALYZE必須指定
*/
if (!(params.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選項則設定所有freeze ages為0.
* 否則的話,傳遞-1(即使用預設值).
*/
if (params.options & 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" */
//使用者呼叫的vacuum永遠不會是wraparound
params.is_wraparound = false;
/* user-invoked vacuum never uses this parameter */
//使用者呼叫vacuum永遠不會使用該引數
params.log_min_duration = -1;
/* Now go through the common routine */
//呼叫vacuum
vacuum(vacstmt->rels, ¶ms, NULL, isTopLevel);
}
建立測試用例
postgres=# create table t_index_test (id int,v1 char(8),v2 varchar(16));
CREATE TABLE
postgres=# alter table t_index_test add constraint pk_t_index_test primary key(id);
ALTER TABLE
postgres=# insert into t_index_test select generate_series(1,10), concat('v1-', generate_series(1,10)::varchar), concat('v2-', generate_series(1,10)::varchar);
INSERT 0 10
postgres=# select * from t_index_test;
id | v1 | v2
----+----------+-------
1 | v1-1 | v2-1
2 | v1-2 | v2-2
3 | v1-3 | v2-3
4 | v1-4 | v2-4
5 | v1-5 | v2-5
6 | v1-6 | v2-6
7 | v1-7 | v2-7
8 | v1-8 | v2-8
9 | v1-9 | v2-9
10 | v1-10 | v2-10
(10 rows)
postgres=# select pg_backend_pid();
pg_backend_pid
----------------
16227
(1 row)
postgres=# VACUUM (VERBOSE, ANALYZE) t_index_test;
gdb 斷點，檢視函式呼叫棧
(gdb) b ExecVacuum
Breakpoint 1 at 0x562e5d12cab0: file vacuum.c, line 89.
(gdb) c
Continuing.
Breakpoint 1, ExecVacuum (pstate=pstate@entry=0x562e5f32e1c0, vacstmt=vacstmt@entry=0x562e5f253970, isTopLevel=isTopLevel@entry=true) at vacuum.c:89
89 {
(gdb) bt
#0 ExecVacuum (pstate=pstate@entry=0x562e5f32e1c0, vacstmt=vacstmt@entry=0x562e5f253970, isTopLevel=isTopLevel@entry=true) at vacuum.c:89
#1 0x0000562e5d29408b in standard_ProcessUtility (pstmt=0x562e5f253c90, queryString=0x562e5f252d70 "VACUUM (VERBOSE, ANALYZE) t_index_test;", context=<optimized out>,
params=0x0, queryEnv=0x0, dest=0x562e5f253d70, completionTag=0x7ffc6ec73380 "") at utility.c:670
#2 0x0000562e5d290ec4 in PortalRunUtility (portal=0x562e5f2bacd0, pstmt=0x562e5f253c90, isTopLevel=<optimized out>, setHoldSnapshot=<optimized out>, dest=0x562e5f253d70,
completionTag=0x7ffc6ec73380 "") at pquery.c:1175
#3 0x0000562e5d291980 in PortalRunMulti (portal=portal@entry=0x562e5f2bacd0, isTopLevel=isTopLevel@entry=true, setHoldSnapshot=setHoldSnapshot@entry=false,
dest=dest@entry=0x562e5f253d70, altdest=altdest@entry=0x562e5f253d70, completionTag=completionTag@entry=0x7ffc6ec73380 "") at pquery.c:1321
#4 0x0000562e5d29255a in PortalRun (portal=portal@entry=0x562e5f2bacd0, count=count@entry=9223372036854775807, isTopLevel=isTopLevel@entry=true, run_once=run_once@entry=true,
dest=dest@entry=0x562e5f253d70, altdest=altdest@entry=0x562e5f253d70, completionTag=0x7ffc6ec73380 "") at pquery.c:796
#5 0x0000562e5d28e685 in exec_simple_query (query_string=0x562e5f252d70 "VACUUM (VERBOSE, ANALYZE) t_index_test;") at postgres.c:1215
#6 0x0000562e5d28feab in PostgresMain (argc=<optimized out>, argv=argv@entry=0x562e5f27ee18, dbname=<optimized out>, username=<optimized out>) at postgres.c:4247
#7 0x0000562e5d218bdf in BackendRun (port=0x562e5f277310, port=0x562e5f277310) at postmaster.c:4437
#8 BackendStartup (port=0x562e5f277310) at postmaster.c:4128
#9 ServerLoop () at postmaster.c:1704
#10 0x0000562e5d219b30 in PostmasterMain (argc=3, argv=0x562e5f24ea40) at postmaster.c:1377
#11 0x0000562e5cf9add8 in main (argc=3, argv=0x562e5f24ea40) at main.c:228
除錯觀察
(gdb) n
101 params.truncate = VACOPT_TERNARY_DEFAULT;
(gdb) p *pstate
$1 = {parentParseState = 0x0, p_sourcetext = 0x562e5f252d70 "VACUUM (VERBOSE, ANALYZE) t_index_test;", p_rtable = 0x0, p_joinexprs = 0x0, p_joinlist = 0x0, p_namespace = 0x0,
p_lateral_active = false, p_ctenamespace = 0x0, p_future_ctes = 0x0, p_parent_cte = 0x0, p_target_relation = 0x0, p_target_rangetblentry = 0x0, p_is_insert = false,
p_windowdefs = 0x0, p_expr_kind = EXPR_KIND_NONE, p_next_resno = 1, p_multiassign_exprs = 0x0, p_locking_clause = 0x0, p_locked_from_parent = false, p_resolve_unknowns = true,
p_queryEnv = 0x0, p_hasAggs = false, p_hasWindowFuncs = false, p_hasTargetSRFs = false, p_hasSubLinks = false, p_hasModifyingCTE = false, p_last_srf = 0x0,
p_pre_columnref_hook = 0x0, p_post_columnref_hook = 0x0, p_paramref_hook = 0x0, p_coerce_param_hook = 0x0, p_ref_hook_state = 0x0}
(gdb) p *vacstmt
$2 = {type = T_VacuumStmt, options = 0x562e5f2537e0, rels = 0x562e5f253940, is_vacuumcmd = true}
(gdb) p vacstmt->options
$3 = (List *) 0x562e5f2537e0
(gdb) p vacstmt->options->next
There is no member named next.
結構體
/* ----------------------
* Vacuum and Analyze Statements
* Vacuum和Analyze宣告
*
* Even though these are nominally two statements, it's convenient to use
* just one node type for both.
* 雖然在這裡有兩種不同的宣告,但只需要使用統一的Node型別即可.
* @lguan
* 意思是Vacuum和Analyze使用同一個宣告，只是用NodeTag來區分？
* ----------------------
*/
typedef struct VacuumStmt
{
NodeTag type;
List *options; /* list of DefElem nodes */
//VacuumRelation連結串列,如為NIL-->所有Relation.
List *rels; /* list of VacuumRelation, or NIL for all */
//true則表示VACCUM，false表示ANALYZE
bool is_vacuumcmd; /* true for VACUUM, false for ANALYZE */
} VacuumStmt;
其中options即為使用者輸入的option，在本例中為“VERBOSE”和“ANALYZE”
option為一個連結串列，這時PG中通用的一個連結串列結構體
typedef struct List
{
NodeTag type; /* T_List, T_IntList, or T_OidList */
int length;
ListCell *head;
ListCell *tail;
} List;
struct ListCell
{
union
{
void *ptr_value;
int int_value;
Oid oid_value;
} data;
ListCell *next;
};
繼續除錯
(gdb) n
104 foreach(lc, vacstmt->options)
(gdb) n
106 DefElem *opt = (DefElem *) lfirst(lc);
(gdb) n
109 if (strcmp(opt->defname, "verbose") == 0)
(gdb) p *opt
$4 = {type = T_DefElem, defnamespace = 0x0, defname = 0x562e5f253758 "verbose", arg = 0x0, defaction = DEFELEM_UNSPEC, location = 8}
可以看到為第一個引數“verbose”，這裡應該是前面的解析程式碼中做了轉換，大寫轉換成小寫。
看一下foreach和lfirst宏
#define foreach(cell, l) \ for ((cell) = list_head(l); (cell) != NULL; (cell) = lnext(cell))
#define lfirst(lc) ((lc)->data.ptr_value)
可以看到option這個連結串列中的節點指標所指向的位置是一個DefElem的結構體，由於封裝原因，所以在連結串列中是一個void型別的指標，可以指向任意的型別，所以可以猜測在前面的呼叫函式中，在構建VacuumStmt結構體時應該已經option連結串列中的節點實際資料設定成了DefElem，（這裡只是個人猜測，這一程式碼值得深入連線以下，因為PG出現大量的這種型別的寫法，具有模擬c++類，封裝的實現的意思）。
看以下DefElem結構體
/*
* DefElem - a generic "name = value" option definition
* @lguan
* DefElem - 通用的“name=value”的選項的定義，就是說該選項的名字即為該選項的值
*
* In some contexts the name can be qualified. Also, certain SQL commands
* allow a SET/ADD/DROP action to be attached to option settings, so it's
* convenient to carry a field for that too. (Note: currently, it is our
* practice that the grammar allows namespace and action only in statements
* where they are relevant; C code can just ignore those fields in other
* statements.)
* @lguan
* 在某些語境下，名稱可以是限定的。
* 此外，某些 SQL 命令允許將 SET/ADD/DROP 操作附加到選項設定，因此攜帶欄位也很方便。
*/
typedef enum DefElemAction
{
DEFELEM_UNSPEC, /* no action given */
DEFELEM_SET,
DEFELEM_ADD,
DEFELEM_DROP
} DefElemAction;
typedef struct DefElem
{
NodeTag type;
char *defnamespace; /* NULL if unqualified name */
char *defname;
Node *arg; /* a (Value *) or a (TypeName *) */
DefElemAction defaction; /* unspecified action, or SET/ADD/DROP */
int location; /* token location, or -1 if unknown */
} DefElem;
繼續除錯
(gdb) n
110 verbose = defGetBoolean(opt);
(gdb) n
106 DefElem *opt = (DefElem *) lfirst(lc);
(gdb) p verbose
$5 = true
(gdb) n
109 if (strcmp(opt->defname, "verbose") == 0)
(gdb) p *opt
$6 = {type = T_DefElem, defnamespace = 0x0, defname = 0x562e5d566c01 "analyze", arg = 0x0, defaction = DEFELEM_UNSPEC, location = 17}
(gdb) n
111 else if (strcmp(opt->defname, "skip_locked") == 0)
(gdb) n
113 else if (!vacstmt->is_vacuumcmd)
(gdb) n
120 else if (strcmp(opt->defname, "analyze") == 0)
(gdb) n
121 analyze = defGetBoolean(opt);
(gdb) n
下個引數和之前的一樣的邏輯，掠過
繼續除錯
(gdb) n
140 params.options =
(gdb) p analyze
$7 = <optimized out>
(gdb) n
158 if (!(params.options & VACOPT_ANALYZE))
(gdb) p analyze
$8 = <optimized out>
(gdb) p params
$9 = {options = 7, freeze_min_age = 0, freeze_table_age = 1598457328, multixact_freeze_min_age = 22062, multixact_freeze_table_age = 1598458104, is_wraparound = 46,
log_min_duration = 208, index_cleanup = VACOPT_TERNARY_DEFAULT, truncate = VACOPT_TERNARY_DEFAULT}
(gdb) n
177 if (params.options & VACOPT_FREEZE)
(gdb) n
189 params.multixact_freeze_table_age = -1;
(gdb) n
193 params.is_wraparound = false;
(gdb) n
196 params.log_min_duration = -1;
(gdb) n
199 vacuum(vacstmt->rels, ¶ms, NULL, isTopLevel);
(gdb) p params
$10 = {options = 7, freeze_min_age = -1, freeze_table_age = -1, multixact_freeze_min_age = -1, multixact_freeze_table_age = -1, is_wraparound = false, log_min_duration = -1,
index_cleanup = VACOPT_TERNARY_DEFAULT, truncate = VACOPT_TERNARY_DEFAULT}
(gdb)
後面就是在設定結構體VacuumParams的值了
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;
/*
* A ternary value used by vacuum parameters.
* vacuum的引數的三元值
*
* DEFAULT value is used to determine the value based on other
* configurations, e.g. reloptions.
* 預設值代表該引數是基於其他的配置的，比如說：對應關係（表）的選項
*/
typedef enum VacOptTernaryValue
{
VACOPT_TERNARY_DEFAULT = 0,
VACOPT_TERNARY_DISABLED,
VACOPT_TERNARY_ENABLED,
} VacOptTernaryValue;
/*
* Parameters customizing behavior of VACUUM and ANALYZE.
* 客戶端呼叫VACUUM/ANALYZE時的定製化引數
*
* Note that at least one of VACOPT_VACUUM and VACOPT_ANALYZE must be set
* in options.
* 注意至少VACOPT_VACUUM/VACOPT_ANALYZE在選項中設定.
*/
typedef struct VacuumParams
{
int options; /* bitmask of VacuumOption VacuumOption的位掩碼*/
//最小freeze age,-1表示使用預設
int freeze_min_age; /* min freeze age, -1 to use default */
//當freeze age 達到 freeze_table_age 時需要掃描整個table
int freeze_table_age; /* age at which to scan whole table */
//最小的multixact freeze age,-1表示預設
int multixact_freeze_min_age; /* min multixact freeze age, -1 to
* use default */
//當min multixact freeze age 達到 multixact_freeze_table_age 時需要掃描整個table
int multixact_freeze_table_age; /* multixact age at which to scan
* whole table */
//是否強制wraparound?
bool is_wraparound; /* force a for-wraparound vacuum */
//以毫秒為單位的最小執行閾值
int log_min_duration; /* minimum execution threshold in ms at
* which verbose logs are activated, -1
* to use default */
//進行索引vacuum和清理，預設值由索引對應的表的選項來決定
VacOptTernaryValue index_cleanup; /* Do index vacuum and cleanup,
* default value depends on reloptions */
//在末尾截斷空頁，預設值由對應的表的選項決定
VacOptTernaryValue truncate; /* Truncate empty pages at the end,
* default value depends on reloptions */
} VacuumParams;
這裡用了一個區域性變數params作為引數，呼叫vacuum主實現函式。
在本例中沒有進入
if (!(params.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")));
}
}
所以沒有觀察到vacstmt->rels這個連結串列的結構，因此，再除錯一次，去掉ANALYZE選項。
結構體
/*
* Info about a single target table of VACUUM/ANALYZE.
* VACUUM/ANALYZE命令的目標表資訊.
*
* 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.
* 如設定了OID欄位,該值通常是將要處理的資料表的oid值，那麼關係欄位可以為NULL。
* 如果不是，則僅用於報告未能開啟/鎖定關係。
*/
typedef struct VacuumRelation
{
NodeTag type;
RangeVar *relation; /* table name to process, or NULL */
Oid oid; /* table's OID; InvalidOid if not looked up */
//表的列欄位名，如果是NIL表示VACUUM所有列
List *va_cols; /* list of column names, or NIL for all */
} VacuumRelation;
然後根據gdb結果
(gdb) p *vrel
$6 = {type = T_VacuumRelation, relation = 0x562e5f253758, oid = 0, va_cols = 0x0}
oid欄位為0，不知道是不是註釋有誤的原因？？？？？
看一下結構體
/*
* RangeVar - range variable, used in FROM clauses
* RangeVar - 範圍變數，用於 FROM 子句
*
* Also used to represent table names in utility statements; there, the alias
* field is not used, and inh tells whether to apply the operation
* recursively to child tables. In some contexts it is also useful to carry
* a TEMP table indication here.
* 也用於表示實用程式語句中的表名。這種情況下，沒有使用alias欄位，並且 inh 用於表示是否將操作遞迴地應用於子表。
* 在某些情況下，在此處攜帶 TEMP 表指示也很有用。？？？？
*/
typedef struct RangeVar
{
NodeTag type;
char *catalogname; /* the catalog (database) name, or NULL */
char *schemaname; /* the schema name, or NULL */
char *relname; /* the relation/sequence name */
bool inh; /* expand rel by inheritance? recursively act
* on children? */
char relpersistence; /* see RELPERSISTENCE_* in pg_class.h */
Alias *alias; /* table alias & optional column aliases */
int location; /* token location, or -1 if unknown */
} RangeVar;
(gdb) p *(RangeVar *)(vrel->relation)
$10 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x562e5f253738 "t_index_test", inh = true, relpersistence = 112 'p', alias = 0x0, location = 15}
(gdb)
基本除錯完成。
總結如下，
結構體VacuumStmt是vacuum的主結構體，其中的option連結串列是用於輸入引數的連結串列集合，該連結串列中的節點型別應該是DefElem結構體，rels連結串列是使用者想要進行vacuum的表的集合，該連結串列的節點型別為VacuumRelation結構體。
而VacuumParams結構體中儲存的是進行vacuum操作時的一些配置引數，其中的option和上面的option不是一樣，這裡的option是透過解析上面的option，再透過VacuumOption這個結構體，生成的一個位掩碼，來代表再上面的option（也就是使用者輸入的vacuum選項）
再次感謝
大神這種分享知識的精神也正符合PG開源社群的宗旨。
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/70012752/viewspace-2884353/，如需轉載，請註明出處，否則將追究法律責任。
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