本篇內(nèi)容主要講解“PostgreSQL中vacuum過程分析”，感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷，實(shí)用性強(qiáng)。下面就讓小編來帶大家學(xué)習(xí)“PostgreSQL中vacuum過程分析”吧!
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宏定義
Vacuum和Analyze命令選項(xiàng)
重慶分公司
重慶分公司
/* ----------------------
* Vacuum and Analyze Statements
* Vacuum和Analyze命令選項(xiàng)
*
* 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.
* 雖然在這里有兩種不同的語句,但只需要使用統(tǒng)一的Node類型即可.
* 注意至少VACOPT_VACUUM/VACOPT_ANALYZE在選項(xiàng)中設(shè)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
存儲(chǔ)vacuum命令的option&Relation鏈表
typedef struct VacuumStmt
{
NodeTag type;//Tag
//VacuumOption位標(biāo)記
int options; /* OR of VacuumOption flags */
//VacuumRelation鏈表,如為NIL-->所有Relation.
List *rels; /* list of VacuumRelation, or NIL for all */
} VacuumStmt;VacuumParams
vacuum命令參數(shù)
/*
* Parameters customizing behavior of VACUUM and ANALYZE.
* 客戶端調(diào)用VACUUM/ANALYZE時(shí)的定制化參數(shù)
*/
typedef struct VacuumParams
{
//最小freeze age,-1表示使用默認(rèn)
int freeze_min_age; /* min freeze age, -1 to use default */
//掃描整個(gè)table的freeze age
int freeze_table_age; /* age at which to scan whole table */
//最小的multixact freeze age,-1表示默認(rèn)
int multixact_freeze_min_age; /* min multixact freeze age, -1 to
* use default */
//掃描全表的freeze age,-1表示默認(rèn)
int multixact_freeze_table_age; /* multixact age at which to scan
* whole table */
//是否強(qiáng)制wraparound?
bool is_wraparound; /* force a for-wraparound vacuum */
//以毫秒為單位的最小執(zhí)行閾值
int log_min_duration; /* minimum execution threshold in ms at
* which verbose logs are activated, -1
* to use default */
} VacuumParams;VacuumRelation
VACUUM/ANALYZE命令的目標(biāo)表信息
/*
* Info about a single target table of VACUUM/ANALYZE.
* VACUUM/ANALYZE命令的目標(biāo)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.
* 如設(shè)置了OID字段,該值通常是將要處理的數(shù)據(jù)表.
* 那么關(guān)系字段可以為空;如果不是，則僅用于報(bào)告未能打開/鎖定關(guān)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;vacuum是VACUUM/ANALYZE命令的內(nèi)部處理入口.
邏輯比較簡單:
1.配置vacuum處理的相關(guān)參數(shù),如命令類型等
2.執(zhí)行相關(guān)檢查
3.構(gòu)造vacuum處理上下文
4.構(gòu)造vacuum需處理的relation鏈表
5.循環(huán)遍歷relation鏈表
5.1 獲取relation
5.2 執(zhí)行vacuum_rel
6.收尾工作
/*
* Internal entry point for VACUUM and ANALYZE commands.
* VACUUM/ANALYZE命令的內(nèi)部處理入口
*
* options is a bitmask of VacuumOption flags, indicating what to do.
* options是VacuumOption選項(xiàng)標(biāo)記位,指示應(yīng)該做什么.
*
* relations, if not NIL, is a list of VacuumRelation to process; otherwise,
* we process all relevant tables in the database. For each VacuumRelation,
* if a valid OID is supplied, the table with that OID is what to process;
* otherwise, the VacuumRelation's RangeVar indicates what to process.
* relations,如果不是空指針NIL,那么存儲(chǔ)了待處理的VacuumRelation結(jié)構(gòu)體鏈表.
* 如為NIL,將處理數(shù)據(jù)庫中的所有相關(guān)數(shù)據(jù)表.
* 對(duì)每一個(gè)VacuumRelation,如提供了有效OID,該OID對(duì)應(yīng)table就會(huì)被處理,
* 否則,VacuumRelation的RangeVar指示了如何處理.
*
* params contains a set of parameters that can be used to customize the
* behavior.
* params是客戶端定制的參數(shù)集合.
*
* bstrategy is normally given as NULL, but in autovacuum it can be passed
* in to use the same buffer strategy object across multiple vacuum() calls.
* bstrategy通常是NULL,但在autovacuum中,
* 該參數(shù)可用于指示在多個(gè)vacuum()調(diào)用中使用同樣的緩存strategy object
*
* isTopLevel should be passed down from ProcessUtility.
* isTopLevel通過ProcessUtility向下傳遞
*
* It is the caller's responsibility that all parameters are allocated in a
* memory context that will not disappear at transaction commit.
* 調(diào)用者應(yīng)確保所有的參數(shù)在同一個(gè)內(nèi)存上下文分配內(nèi)存,而不會(huì)在事務(wù)commit時(shí)突然消失.
*/
void
vacuum(int options, List *relations, VacuumParams *params,
BufferAccessStrategy bstrategy, bool isTopLevel)
{
static bool in_vacuum = false;//是否在vacuum
const char *stmttype;//語句類型,vacuum?analyze?
volatile bool in_outer_xact,
use_own_xacts;
Assert(params != NULL);
stmttype = (options & VACOPT_VACUUM) ? "VACUUM" : "ANALYZE";
/*
* We cannot run VACUUM inside a user transaction block; if we were inside
* a transaction, then our commit- and start-transaction-command calls
* would not have the intended effect! There are numerous other subtle
* dependencies on this, too.
* 不能在用戶事務(wù)塊中運(yùn)行VACUUM,如果我們在事務(wù)塊中,
* 那么處理過程中的commit-和start-transaction-command調(diào)用不會(huì)有正確的效果.
* 而且還有許多其他微妙的依賴關(guān)系。
*
* ANALYZE (without VACUUM) can run either way.
* ANALYZE(不帶VACUUM)則沒有此問題.
*/
if (options & VACOPT_VACUUM)
{
PreventInTransactionBlock(isTopLevel, stmttype);
in_outer_xact = false;
}
else
in_outer_xact = IsInTransactionBlock(isTopLevel);
/*
* Due to static variables vac_context, anl_context and vac_strategy,
* vacuum() is not reentrant. This matters when VACUUM FULL or ANALYZE
* calls a hostile index expression that itself calls ANALYZE.
* 鑒于vac_context, anl_context and vac_strategy這是變量都是靜態(tài)變量,
* 因此vacuum()函數(shù)是不能重入的(狀態(tài)已出現(xiàn)變化).
* 在VACUUM FULL或者ANALYZE調(diào)用了hostile index expression,
* 而此邏輯又調(diào)用了ANALYZE時(shí)會(huì)出現(xiàn)此情況,務(wù)必注意.
*/
if (in_vacuum)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("%s cannot be executed from VACUUM or ANALYZE",
stmttype)));
/*
* Sanity check DISABLE_PAGE_SKIPPING option.
* 檢查
*/
if ((options & VACOPT_FULL) != 0 &&
(options & VACOPT_DISABLE_PAGE_SKIPPING) != 0)
ereport(ERROR,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("VACUUM option DISABLE_PAGE_SKIPPING cannot be used with FULL")));
/*
* Send info about dead objects to the statistics collector, unless we are
* in autovacuum --- autovacuum.c does this for itself.
* 發(fā)送dead objects的統(tǒng)計(jì)信息給收集器,除非我們在autovacuum中
* -- autovacuum.c會(huì)自己做這個(gè)事情.
*/
if ((options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess())
pgstat_vacuum_stat();
/*
* Create special memory context for cross-transaction storage.
* 跨事務(wù)存儲(chǔ),需要?jiǎng)?chuàng)建特別的內(nèi)存上下文.
*
* Since it is a child of PortalContext, it will go away eventually even
* if we suffer an error; there's no need for special abort cleanup logic.
* 因?yàn)檫@是PortalContext的子對(duì)象,即使我們犯了錯(cuò)誤，它最終也會(huì)消失;不需要特殊的中止清理邏輯。
*/
vac_context = AllocSetContextCreate(PortalContext,
"Vacuum",
ALLOCSET_DEFAULT_SIZES);
/*
* If caller didn't give us a buffer strategy object, make one in the
* cross-transaction memory context.
* 如果調(diào)用者沒有提供buffer strategy object,
* 在跨事務(wù)的內(nèi)存上下文中創(chuàng)建一個(gè).
*/
if (bstrategy == NULL)
{
MemoryContext old_context = MemoryContextSwitchTo(vac_context);
bstrategy = GetAccessStrategy(BAS_VACUUM);
MemoryContextSwitchTo(old_context);
}
vac_strategy = bstrategy;
/*
* Build list of relation(s) to process, putting any new data in
* vac_context for safekeeping.
* 構(gòu)建要處理的關(guān)系列表，將所有新數(shù)據(jù)放入vac_context中以進(jìn)行安全(位于vacuum上下文中)保存。
*/
if (relations != NIL)
{
List *newrels = NIL;
ListCell *lc;
foreach(lc, relations)
{
VacuumRelation *vrel = lfirst_node(VacuumRelation, lc);
List *sublist;
MemoryContext old_context;
sublist = expand_vacuum_rel(vrel, options);
old_context = MemoryContextSwitchTo(vac_context);
newrels = list_concat(newrels, sublist);
MemoryContextSwitchTo(old_context);
}
relations = newrels;
}
else
relations = get_all_vacuum_rels(options);
/*
* Decide whether we need to start/commit our own transactions.
* 確定是否需要start/commit自己的事務(wù)
*
* For VACUUM (with or without ANALYZE): always do so, so that we can
* release locks as soon as possible. (We could possibly use the outer
* transaction for a one-table VACUUM, but handling TOAST tables would be
* problematic.)
* 對(duì)于VACUUM(包含或不包含ANALYZE):通常需要這樣處理,以便我們可以盡可能快的釋放鎖.
* (對(duì)于一張表的VACUUM,我們可能使用外層事務(wù),但處理TOAST表是會(huì)有問題)
*
* For ANALYZE (no VACUUM): if inside a transaction block, we cannot
* start/commit our own transactions. Also, there's no need to do so if
* only processing one relation. For multiple relations when not within a
* transaction block, and also in an autovacuum worker, use own
* transactions so we can release locks sooner.
* 對(duì)于ANALYZE(沒有VACUUM選項(xiàng)):如果在事務(wù)塊中,我們不能start/commit自己的事務(wù).
* 同時(shí),如果只需要處理一個(gè)relation,則不需要這樣處理.
* 對(duì)于不在一個(gè)事務(wù)塊中的多個(gè)relations/在autovacuum worker中,
* 使用自己的事務(wù)以便更快的釋放鎖.
*/
if (options & VACOPT_VACUUM)
use_own_xacts = true;
else
{
Assert(options & VACOPT_ANALYZE);
if (IsAutoVacuumWorkerProcess())
use_own_xacts = true;
else if (in_outer_xact)
use_own_xacts = false;
else if (list_length(relations) > 1)
use_own_xacts = true;
else
use_own_xacts = false;
}
/*
* vacuum_rel expects to be entered with no transaction active; it will
* start and commit its own transaction. But we are called by an SQL
* command, and so we are executing inside a transaction already. We
* commit the transaction started in PostgresMain() here, and start
* another one before exiting to match the commit waiting for us back in
* PostgresMain().
* 在進(jìn)入vacuum_rel前,不希望存在事務(wù)活動(dòng).該函數(shù)會(huì)啟動(dòng)和提交自己的事務(wù).
* 但由于我們是通過SQL命令調(diào)用的,因此我們已處于事務(wù)中執(zhí)行.
* 在這里我們提交在PostgresMain()中啟動(dòng)的事務(wù),
* 并在退出之前啟動(dòng)另一個(gè)，以匹配在PostgresMain()中等待我們的提交。
*/
if (use_own_xacts)
{
Assert(!in_outer_xact);
/* ActiveSnapshot is not set by autovacuum */
//autovacuum不會(huì)設(shè)置ActiveSnapshot
if (ActiveSnapshotSet())
PopActiveSnapshot();
/* matches the StartTransaction in PostgresMain() */
//匹配PostgresMain()中的StartTransaction
CommitTransactionCommand();
}
/* Turn vacuum cost accounting on or off, and set/clear in_vacuum */
//設(shè)置vacuum成本計(jì)數(shù)on/off,并set/clear in_vacuum參數(shù)
PG_TRY();
{
ListCell *cur;
in_vacuum = true;
VacuumCostActive = (VacuumCostDelay > 0);
VacuumCostBalance = 0;
VacuumPageHit = 0;
VacuumPageMiss = 0;
VacuumPageDirty = 0;
/*
* Loop to process each selected relation.
* 循環(huán)處理每一個(gè)已選中的relation.
*/
foreach(cur, relations)
{
VacuumRelation *vrel = lfirst_node(VacuumRelation, cur);
if (options & VACOPT_VACUUM)
{
//執(zhí)行vacuum處理
if (!vacuum_rel(vrel->oid, vrel->relation, options, params))
continue;
}
if (options & VACOPT_ANALYZE)
{
/*
* If using separate xacts, start one for analyze. Otherwise,
* we can use the outer transaction.
* 如果使用獨(dú)立的xacts,為analyze啟動(dòng)一個(gè)何事務(wù).
* 否則,我們可以使用外層事務(wù).
*/
if (use_own_xacts)
{
//使用自己的事務(wù)
StartTransactionCommand();
/* functions in indexes may want a snapshot set */
//快照壓棧
PushActiveSnapshot(GetTransactionSnapshot());
}
//分析relation
analyze_rel(vrel->oid, vrel->relation, options, params,
vrel->va_cols, in_outer_xact, vac_strategy);
if (use_own_xacts)
{
//使用自己的事務(wù),出棧
PopActiveSnapshot();
//提交事務(wù)
CommitTransactionCommand();
}
}
}
}
PG_CATCH();
{
in_vacuum = false;
VacuumCostActive = false;
PG_RE_THROW();
}
PG_END_TRY();
in_vacuum = false;
VacuumCostActive = false;
/*
* Finish up processing.
* 完成處理過程
*/
if (use_own_xacts)
{
/* here, we are not in a transaction */
//在這里,沒有處于事務(wù)中
/*
* This matches the CommitTransaction waiting for us in
* PostgresMain().
* 匹配在PostgresMain()函數(shù)中等待我們的CommitTransaction.
*/
StartTransactionCommand();
}
if ((options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess())
{
/*
* Update pg_database.datfrozenxid, and truncate pg_xact if possible.
* (autovacuum.c does this for itself.)
* 更新pg_database.datfrozenxid,如可能截?cái)鄍g_xact.
* (autovacuum.c不會(huì)處理這事情)
*/
vac_update_datfrozenxid();
}
/*
* Clean up working storage --- note we must do this after
* StartTransactionCommand, else we might be trying to delete the active
* context!
* 清除工作存儲(chǔ) --- 注意必須在StartTransactionCommand命令后執(zhí)行清除過程,
* 否則我們可能會(huì)嘗試刪除活動(dòng)的上下文.
*/
MemoryContextDelete(vac_context);
vac_context = NULL;
}測試腳本
17:19:28 (xdb@[local]:5432)testdb=# vacuum t1;
啟動(dòng)gdb,設(shè)置斷點(diǎn)
(gdb) b vacuum Breakpoint 1 at 0x6b9b8c: file vacuum.c, line 175. (gdb) c Continuing. Breakpoint 1, vacuum (options=1, relations=0x2294988, params=0x7fff403d8880, bstrategy=0x0, isTopLevel=true) at vacuum.c:175 175 Assert(params != NULL); (gdb)
輸入?yún)?shù)
options=1 —> VACOPT_VACUUM
relations=0x2294988,relation鏈表,里面只有一個(gè)item,即t1
params=0x7fff403d8880,默認(rèn)參數(shù)
bstrategy=NULL,
isTopLevel=T,為頂層事務(wù)
(gdb) p *params
$2 = {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}
(gdb)變量賦值并執(zhí)行相關(guān)判斷
(gdb) n 177 stmttype = (options & VACOPT_VACUUM) ? "VACUUM" : "ANALYZE"; (gdb) 187 if (options & VACOPT_VACUUM) (gdb) 189 PreventInTransactionBlock(isTopLevel, stmttype); (gdb) 190 in_outer_xact = false; (gdb) 200 if (in_vacuum) (gdb) 209 if ((options & VACOPT_FULL) != 0 && (gdb)
統(tǒng)計(jì)信息
219 if ((options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess()) (gdb) 220 pgstat_vacuum_stat(); (gdb)
創(chuàng)建并設(shè)置內(nèi)存上下文
(gdb) n 228 vac_context = AllocSetContextCreate(PortalContext, (gdb) 236 if (bstrategy == NULL) (gdb) 238 MemoryContext old_context = MemoryContextSwitchTo(vac_context); (gdb) 240 bstrategy = GetAccessStrategy(BAS_VACUUM); (gdb) 241 MemoryContextSwitchTo(old_context); (gdb) 243 vac_strategy = bstrategy; (gdb) 249 if (relations != NIL) (gdb)
構(gòu)造VacuumRelation鏈表
(gdb)
251 List *newrels = NIL;
(gdb)
254 foreach(lc, relations)
(gdb)
256 VacuumRelation *vrel = lfirst_node(VacuumRelation, lc);
(gdb)
260 sublist = expand_vacuum_rel(vrel);
(gdb) p *vrel
$3 = {type = T_VacuumRelation, relation = 0x22948d0, oid = 0, va_cols = 0x0}
(gdb) p *vrel->relation
$4 = {type = T_RangeVar, catalogname = 0x0, schemaname = 0x0, relname = 0x22948b0 "t1", inh = true,
relpersistence = 112 'p', alias = 0x0, location = 7}
(gdb)
(gdb) n
261 old_context = MemoryContextSwitchTo(vac_context);
(gdb)
262 newrels = list_concat(newrels, sublist);
(gdb)
263 MemoryContextSwitchTo(old_context);
(gdb)
254 foreach(lc, relations)
(gdb)
265 relations = newrels;
(gdb)使用自主事務(wù)
284 if (options & VACOPT_VACUUM) (gdb) 285 use_own_xacts = true; (gdb) 307 if (use_own_xacts) (gdb) 307 if (use_own_xacts) (gdb) 309 Assert(!in_outer_xact); (gdb) 312 if (ActiveSnapshotSet()) (gdb) 313 PopActiveSnapshot(); (gdb) 316 CommitTransactionCommand(); (gdb) 320 PG_TRY(); (gdb)
開始執(zhí)行,設(shè)置vacuum成本計(jì)數(shù)on/off,并set/clear in_vacuum參數(shù)
(gdb) 324 in_vacuum = true; (gdb) 325 VacuumCostActive = (VacuumCostDelay > 0); (gdb) 326 VacuumCostBalance = 0; (gdb) 327 VacuumPageHit = 0; (gdb) 328 VacuumPageMiss = 0; (gdb) 329 VacuumPageDirty = 0; (gdb)
循環(huán)relation,調(diào)用vacuum_rel
334 foreach(cur, relations) (gdb) 336 VacuumRelation *vrel = lfirst_node(VacuumRelation, cur); (gdb) 338 if (options & VACOPT_VACUUM) (gdb) 340 if (!vacuum_rel(vrel->oid, vrel->relation, options, params)) (gdb) 344 if (options & VACOPT_ANALYZE) (gdb) 334 foreach(cur, relations) (gdb) 374 PG_END_TRY(); (gdb)
執(zhí)行收尾工作
(gdb) 376 in_vacuum = false; (gdb) 377 VacuumCostActive = false; (gdb) 382 if (use_own_xacts) (gdb) 390 StartTransactionCommand(); (gdb) 393 if ((options & VACOPT_VACUUM) && !IsAutoVacuumWorkerProcess()) (gdb) 399 vac_update_datfrozenxid(); (gdb) 407 MemoryContextDelete(vac_context); (gdb) 408 vac_context = NULL; (gdb)
完成調(diào)用
409 } (gdb) ExecVacuum (vacstmt=0x22949c0, isTopLevel=true) at vacuum.c:142 142 } (gdb)
到此，相信大家對(duì)“PostgreSQL中vacuum過程分析”有了更深的了解，不妨來實(shí)際操作一番吧！這里是創(chuàng)新互聯(lián)網(wǎng)站，更多相關(guān)內(nèi)容可以進(jìn)入相關(guān)頻道進(jìn)行查詢，關(guān)注我們，繼續(xù)學(xué)習(xí)！
