PostgreSQL中vacuum過程HeapTupleSatisfiesVacuum函數(shù)分析
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一、數(shù)據(jù)結(jié)構(gòu)
宏定義
Vacuum和Analyze命令選項(xiàng)
/* ----------------------
* 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(yǔ)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;二、源碼解讀
HeapTupleSatisfiesVacuum
HeapTupleSatisfiesVacuum為VACUUM操作確定元組的狀態(tài).在這里,我們主要想知道的是一個(gè)元組是否可對(duì)所有正在運(yùn)行中的事務(wù)可見.如可見,則不能通過VACUUM刪除該元組.
主要處理流程如下:
0.獲取tuple并執(zhí)行相關(guān)校驗(yàn)
1.條件:插入事務(wù)未提交
1.1條件:無效的xmin,該元組已廢棄可刪除
1.2條件:舊版本(9.0-)的判斷
1.3條件:xmin為當(dāng)前事務(wù)ID
1.4條件:插入事務(wù)非當(dāng)前事務(wù),正在進(jìn)行中
1.5條件:xmin事務(wù)確實(shí)已提交(通過clog判斷)
1.6條件:其他情況
— 至此,可以確定xmin已提交
2.條件:xmax是無效的事務(wù)ID,直接返回LIVE
3.條件:xmax只是鎖定
3.1條件:xmax事務(wù)未提交,分多事務(wù)&非多事務(wù)進(jìn)行判斷
3.2條件:只是鎖定,返回LIVE
4.條件:存在子事務(wù)
4.1條件:xmax正在進(jìn)行,返回事務(wù)進(jìn)行中
4.2條件:xmax已提交,區(qū)分xmax在OldestXmin之前還是之后
4.3條件:xmax不在運(yùn)行中/沒有提交/沒有回滾或崩潰,則設(shè)置xmax為無效事務(wù)ID
4.4默認(rèn)返回LIVE
5.條件:xmax沒有提交
5.1條件:刪除過程中
5.2條件:通過clog判斷,該事務(wù)已提交,設(shè)置事務(wù)標(biāo)記位
5.3條件:其他情況,設(shè)置為無效事務(wù)ID
5.4默認(rèn)返回LIVE
— 至此,可以確定xmax已提交
6.元組xmax≥OldestXmin,最近刪除
7.默認(rèn)元組已DEAD
/*
* HeapTupleSatisfiesVacuum
*
* Determine the status of tuples for VACUUM purposes. Here, what
* we mainly want to know is if a tuple is potentially visible to *any*
* running transaction. If so, it can't be removed yet by VACUUM.
* 為VACUUM確定元組的狀態(tài).
* 在這里,我們主要想知道的是一個(gè)元組是否可對(duì)所有正在運(yùn)行中的事務(wù)可見.
* 如可見,則不能通過VACUUM刪除該元組.
*
* OldestXmin is a cutoff XID (obtained from GetOldestXmin()). Tuples
* deleted by XIDs >= OldestXmin are deemed "recently dead"; they might
* still be visible to some open transaction, so we can't remove them,
* even if we see that the deleting transaction has committed.
* OldestXmin是一個(gè)cutoff XID(通過GetOldestXmin函數(shù)獲得).
* 通過XIDs >= OldestXmin刪除的元組被視為"最近死亡",它們可能仍然對(duì)某些正在進(jìn)行中的事務(wù)可見,
* 因此就算刪除事務(wù)已提交,我們?nèi)匀徊荒芮宄鼈?
*/
HTSV_Result
HeapTupleSatisfiesVacuum(HeapTuple htup, TransactionId OldestXmin,
Buffer buffer)
{
//獲取tuple
HeapTupleHeader tuple = htup->t_data;
//校驗(yàn)
Assert(ItemPointerIsValid(&htup->t_self));
Assert(htup->t_tableOid != InvalidOid);
/*
* Has inserting transaction committed?
* 插入事務(wù)已提交?
*
* If the inserting transaction aborted, then the tuple was never visible
* to any other transaction, so we can delete it immediately.
* 如果插入事務(wù)已回滾,元組對(duì)其他事務(wù)均不可見,因此可以馬上刪除.
*/
if (!HeapTupleHeaderXminCommitted(tuple))
{
//1.插入事務(wù)未提交
if (HeapTupleHeaderXminInvalid(tuple))
//1-1.無效的xmin,該元組已廢棄可刪除
return HEAPTUPLE_DEAD;
/* Used by pre-9.0 binary upgrades */
//用于9.0以前版本的升級(jí),HEAP_MOVED_OFF&HEAP_MOVED_IN已不再使用
else if (tuple->t_infomask & HEAP_MOVED_OFF)
{
TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
if (TransactionIdIsCurrentTransactionId(xvac))
return HEAPTUPLE_DELETE_IN_PROGRESS;
if (TransactionIdIsInProgress(xvac))
return HEAPTUPLE_DELETE_IN_PROGRESS;
if (TransactionIdDidCommit(xvac))
{
SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
InvalidTransactionId);
return HEAPTUPLE_DEAD;
}
SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
InvalidTransactionId);
}
/* Used by pre-9.0 binary upgrades */
//用于9.0以前版本的升級(jí)
else if (tuple->t_infomask & HEAP_MOVED_IN)
{
TransactionId xvac = HeapTupleHeaderGetXvac(tuple);
if (TransactionIdIsCurrentTransactionId(xvac))
return HEAPTUPLE_INSERT_IN_PROGRESS;
if (TransactionIdIsInProgress(xvac))
return HEAPTUPLE_INSERT_IN_PROGRESS;
if (TransactionIdDidCommit(xvac))
SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
InvalidTransactionId);
else
{
SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
InvalidTransactionId);
return HEAPTUPLE_DEAD;
}
}
else if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetRawXmin(tuple)))
{
//1-3.xmin為當(dāng)前事務(wù)ID
if (tuple->t_infomask & HEAP_XMAX_INVALID) /* xid invalid */
//1-3-1.xmax無效,說明插入事務(wù)正在進(jìn)行中
return HEAPTUPLE_INSERT_IN_PROGRESS;
/* only locked? run infomask-only check first, for performance */
//只是鎖定?性能考慮,首先執(zhí)行infomask-only檢查
if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask) ||
HeapTupleHeaderIsOnlyLocked(tuple))
//1-3-2.鎖定狀態(tài)(如for update之類),事務(wù)正在進(jìn)行中
return HEAPTUPLE_INSERT_IN_PROGRESS;
/* inserted and then deleted by same xact */
//插入,然后刪除
if (TransactionIdIsCurrentTransactionId(HeapTupleHeaderGetUpdateXid(tuple)))
//1-3-3.插入,然后刪除
return HEAPTUPLE_DELETE_IN_PROGRESS;
/* deleting subtransaction must have aborted */
//默認(rèn):插入事務(wù)正在進(jìn)行中
return HEAPTUPLE_INSERT_IN_PROGRESS;
}
else if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmin(tuple)))
{
//1-4.插入事務(wù)非當(dāng)前事務(wù),正在進(jìn)行中
/*
* It'd be possible to discern between INSERT/DELETE in progress
* here by looking at xmax - but that doesn't seem beneficial for
* the majority of callers and even detrimental for some. We'd
* rather have callers look at/wait for xmin than xmax. It's
* always correct to return INSERT_IN_PROGRESS because that's
* what's happening from the view of other backends.
* 通過查看xmax，可以區(qū)分正在進(jìn)行的插入/刪除操作 - 但這對(duì)于大多數(shù)調(diào)用者并沒有好處,甚至有害
* 我們寧愿讓調(diào)用者查看/等待xmin而不是xmax。
* 返回INSERT_IN_PROGRESS總是正確的，因?yàn)檫@是從其他后臺(tái)進(jìn)程視圖中看到正在發(fā)生的。
*/
return HEAPTUPLE_INSERT_IN_PROGRESS;
}
else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmin(tuple)))
//1-5.xmin事務(wù)確實(shí)已提交(通過clog判斷)
SetHintBits(tuple, buffer, HEAP_XMIN_COMMITTED,
HeapTupleHeaderGetRawXmin(tuple));
else
{
//1-5.其他情況
//既不在進(jìn)行中,也沒有提交,要么是回滾,要么是崩潰了
/*
* Not in Progress, Not Committed, so either Aborted or crashed
*/
//設(shè)置標(biāo)記位
SetHintBits(tuple, buffer, HEAP_XMIN_INVALID,
InvalidTransactionId);
//返回廢棄標(biāo)記
return HEAPTUPLE_DEAD;
}
/*
* At this point the xmin is known committed, but we might not have
* been able to set the hint bit yet; so we can no longer Assert that
* it's set.
* 在這個(gè)點(diǎn)上,xmin事務(wù)確認(rèn)已提交,但這時(shí)候還是不能設(shè)置hint bit,
* 因此不能斷定已設(shè)置標(biāo)記.
*/
}
/*
* Okay, the inserter committed, so it was good at some point. Now what
* about the deleting transaction?
* 插入數(shù)據(jù)的事務(wù)已提交,現(xiàn)在可以看看刪除事務(wù)的狀態(tài)了.
*/
if (tuple->t_infomask & HEAP_XMAX_INVALID)
//------- 2.xmax是無效的事務(wù)ID,直接返回LIVE
return HEAPTUPLE_LIVE;
if (HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask))
{
//------- 3.鎖定
/*
* "Deleting" xact really only locked it, so the tuple is live in any
* case. However, we should make sure that either XMAX_COMMITTED or
* XMAX_INVALID gets set once the xact is gone, to reduce the costs of
* examining the tuple for future xacts.
* "Deleting"事務(wù)確實(shí)只是鎖定該元組,因此該元組是存活狀態(tài).
* 但是,我們應(yīng)該確保不管是XMAX_COMMITTED還是XMAX_INVALID標(biāo)記,應(yīng)該在事務(wù)完結(jié)后馬上設(shè)置,
* 這樣可以減少為了事務(wù)檢查元組狀態(tài)的成本.
*/
if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
{
//3.1 xmax事務(wù)未提交
if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
{
//3.1.1 多事務(wù)
/*
* If it's a pre-pg_upgrade tuple, the multixact cannot
* possibly be running; otherwise have to check.
* 如果是pre-pg_upgrade元組,多事務(wù)不可能運(yùn)行,否則的話,只能執(zhí)行檢查
*/
if (!HEAP_LOCKED_UPGRADED(tuple->t_infomask) &&
MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple),
true))
return HEAPTUPLE_LIVE;
//其他情況,根據(jù)clog重新設(shè)置事務(wù)狀態(tài)標(biāo)記位
SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
}
else
{
//3.1.2 非多事務(wù)
if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
//xmax事務(wù)正在進(jìn)行,返回LIVE
return HEAPTUPLE_LIVE;
//否則,根據(jù)clog重新設(shè)置事務(wù)狀態(tài)標(biāo)記位
SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
InvalidTransactionId);
}
}
/*
* We don't really care whether xmax did commit, abort or crash. We
* know that xmax did lock the tuple, but it did not and will never
* actually update it.
* 我們確實(shí)不需要真正關(guān)心xmax是否提交/回滾/崩潰.
* 我們知道xmax事務(wù)鎖定了元組,但沒有而且"從未"更新過該元組.
*/
//3.2 只是鎖定,返回LIVE
return HEAPTUPLE_LIVE;
}
if (tuple->t_infomask & HEAP_XMAX_IS_MULTI)
{
//4.存在子事務(wù)
//獲取刪除事務(wù)號(hào)xmax
TransactionId xmax = HeapTupleGetUpdateXid(tuple);
/* already checked above */
Assert(!HEAP_XMAX_IS_LOCKED_ONLY(tuple->t_infomask));
/* not LOCKED_ONLY, so it has to have an xmax */
//根據(jù)上述xmax的判斷,到這里可以肯定xmax是有效的
Assert(TransactionIdIsValid(xmax));
if (TransactionIdIsInProgress(xmax))
//4.1 xmax正在進(jìn)行,返回進(jìn)行中
return HEAPTUPLE_DELETE_IN_PROGRESS;
else if (TransactionIdDidCommit(xmax))
{
//4.2 xmax已提交
/*
* The multixact might still be running due to lockers. If the
* updater is below the xid horizon, we have to return DEAD
* regardless -- otherwise we could end up with a tuple where the
* updater has to be removed due to the horizon, but is not pruned
* away. It's not a problem to prune that tuple, because any
* remaining lockers will also be present in newer tuple versions.
*/
if (!TransactionIdPrecedes(xmax, OldestXmin))
//4.2.1 xmax在OldestXmin之后,
//表示在OldestXmin之后才刪除,返回HEAPTUPLE_RECENTLY_DEAD
return HEAPTUPLE_RECENTLY_DEAD;
//4.2.2 xmax在OldestXmin之前,返回DEAD
return HEAPTUPLE_DEAD;
}
else if (!MultiXactIdIsRunning(HeapTupleHeaderGetRawXmax(tuple), false))
{
/*
* Not in Progress, Not Committed, so either Aborted or crashed.
* Mark the Xmax as invalid.
*/
//4.3 xmax不在運(yùn)行中/沒有提交/沒有回滾或崩潰,則設(shè)置xmax為無效事務(wù)ID
SetHintBits(tuple, buffer, HEAP_XMAX_INVALID, InvalidTransactionId);
}
//4.4 默認(rèn)返回LIVE
return HEAPTUPLE_LIVE;
}
if (!(tuple->t_infomask & HEAP_XMAX_COMMITTED))
{
//5.xmax沒有提交
if (TransactionIdIsInProgress(HeapTupleHeaderGetRawXmax(tuple)))
//5.1 刪除過程中
return HEAPTUPLE_DELETE_IN_PROGRESS;
else if (TransactionIdDidCommit(HeapTupleHeaderGetRawXmax(tuple)))
//5.2 通過clog判斷,該事務(wù)已提交,設(shè)置事務(wù)標(biāo)記位
SetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
HeapTupleHeaderGetRawXmax(tuple));
else
{
/*
* Not in Progress, Not Committed, so either Aborted or crashed
*/
//5.3 其他情況,設(shè)置為無效事務(wù)ID
SetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
InvalidTransactionId);
//返回LIVE
return HEAPTUPLE_LIVE;
}
/*
* At this point the xmax is known committed, but we might not have
* been able to set the hint bit yet; so we can no longer Assert that
* it's set.
*/
//至此,xmax可以確認(rèn)已提交
}
/*
* Deleter committed, but perhaps it was recent enough that some open
* transactions could still see the tuple.
*/
if (!TransactionIdPrecedes(HeapTupleHeaderGetRawXmax(tuple), OldestXmin))
//6.元組xmax≥OldestXmin,最近刪除
return HEAPTUPLE_RECENTLY_DEAD;
/* Otherwise, it's dead and removable */
//7. 默認(rèn)元組已DEAD
return HEAPTUPLE_DEAD;
}到此，相信大家對(duì)“PostgreSQL中vacuum過程HeapTupleSatisfiesVacuum函數(shù)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)！
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