PostgreSQL 原始碼解讀（11）- 插入資料#10（PortalRunMulti和Por...
本文簡單介紹了PG插入資料部分的原始碼，主要內容包括PortalRunMulti函式和PortalRun函式的實現邏輯，PortalRunMulti函式和PortalRun均位於pquery.c檔案中。
一、基礎資訊
PortalRunMulti函式使用的資料結構、宏定義以及依賴的函式等。
資料結構/宏定義
1、Portal
typedef struct PortalData *Portal;
typedef struct PortalData
{
/* Bookkeeping data */
const char *name; /* portal's name */
const char *prepStmtName; /* source prepared statement (NULL if none) */
MemoryContext portalContext; /* subsidiary memory for portal */
ResourceOwner resowner; /* resources owned by portal */
void (*cleanup) (Portal portal); /* cleanup hook */
/*
* State data for remembering which subtransaction(s) the portal was
* created or used in. If the portal is held over from a previous
* transaction, both subxids are InvalidSubTransactionId. Otherwise,
* createSubid is the creating subxact and activeSubid is the last subxact
* in which we ran the portal.
*/
SubTransactionId createSubid; /* the creating subxact */
SubTransactionId activeSubid; /* the last subxact with activity */
/* The query or queries the portal will execute */
const char *sourceText; /* text of query (as of 8.4, never NULL) */
const char *commandTag; /* command tag for original query */
List *stmts; /* list of PlannedStmts */
CachedPlan *cplan; /* CachedPlan, if stmts are from one */
ParamListInfo portalParams; /* params to pass to query */
QueryEnvironment *queryEnv; /* environment for query */
/* Features/options */
PortalStrategy strategy; /* see above */
int cursorOptions; /* DECLARE CURSOR option bits */
bool run_once; /* portal will only be run once */
/* Status data */
PortalStatus status; /* see above */
bool portalPinned; /* a pinned portal can't be dropped */
bool autoHeld; /* was automatically converted from pinned to
* held (see HoldPinnedPortals()) */
/* If not NULL, Executor is active; call ExecutorEnd eventually: */
QueryDesc *queryDesc; /* info needed for executor invocation */
/* If portal returns tuples, this is their tupdesc: */
TupleDesc tupDesc; /* descriptor for result tuples */
/* and these are the format codes to use for the columns: */
int16 *formats; /* a format code for each column */
/*
* Where we store tuples for a held cursor or a PORTAL_ONE_RETURNING or
* PORTAL_UTIL_SELECT query. (A cursor held past the end of its
* transaction no longer has any active executor state.)
*/
Tuplestorestate *holdStore; /* store for holdable cursors */
MemoryContext holdContext; /* memory containing holdStore */
/*
* Snapshot under which tuples in the holdStore were read. We must keep a
* reference to this snapshot if there is any possibility that the tuples
* contain TOAST references, because releasing the snapshot could allow
* recently-dead rows to be vacuumed away, along with any toast data
* belonging to them. In the case of a held cursor, we avoid needing to
* keep such a snapshot by forcibly detoasting the data.
*/
Snapshot holdSnapshot; /* registered snapshot, or NULL if none */
/*
* atStart, atEnd and portalPos indicate the current cursor position.
* portalPos is zero before the first row, N after fetching N'th row of
* query. After we run off the end, portalPos = # of rows in query, and
* atEnd is true. Note that atStart implies portalPos == 0, but not the
* reverse: we might have backed up only as far as the first row, not to
* the start. Also note that various code inspects atStart and atEnd, but
* only the portal movement routines should touch portalPos.
*/
bool atStart;
bool atEnd;
uint64 portalPos;
/* Presentation data, primarily used by the pg_cursors system view */
TimestampTz creation_time; /* time at which this portal was defined */
bool visible; /* include this portal in pg_cursors? */
} PortalData;
2、List
typedef struct ListCell ListCell;
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;
};
3、Snapshot
typedef struct SnapshotData *Snapshot;
/*
* Struct representing all kind of possible snapshots.
*
* There are several different kinds of snapshots:
* * Normal MVCC snapshots
* * MVCC snapshots taken during recovery (in Hot-Standby mode)
* * Historic MVCC snapshots used during logical decoding
* * snapshots passed to HeapTupleSatisfiesDirty()
* * snapshots passed to HeapTupleSatisfiesNonVacuumable()
* * snapshots used for SatisfiesAny, Toast, Self where no members are
* accessed.
*
* TODO: It's probably a good idea to split this struct using a NodeTag
* similar to how parser and executor nodes are handled, with one type for
* each different kind of snapshot to avoid overloading the meaning of
* individual fields.
*/
typedef struct SnapshotData
{
SnapshotSatisfiesFunc satisfies; /* tuple test function */
/*
* The remaining fields are used only for MVCC snapshots, and are normally
* just zeroes in special snapshots. (But xmin and xmax are used
* specially by HeapTupleSatisfiesDirty, and xmin is used specially by
* HeapTupleSatisfiesNonVacuumable.)
*
* An MVCC snapshot can never see the effects of XIDs >= xmax. It can see
* the effects of all older XIDs except those listed in the snapshot. xmin
* is stored as an optimization to avoid needing to search the XID arrays
* for most tuples.
*/
TransactionId xmin; /* all XID < xmin are visible to me */
TransactionId xmax; /* all XID >= xmax are invisible to me */
/*
* For normal MVCC snapshot this contains the all xact IDs that are in
* progress, unless the snapshot was taken during recovery in which case
* it's empty. For historic MVCC snapshots, the meaning is inverted, i.e.
* it contains *committed* transactions between xmin and xmax.
*
* note: all ids in xip[] satisfy xmin <= xip[i] < xmax
*/
TransactionId *xip;
uint32 xcnt; /* # of xact ids in xip[] */
/*
* For non-historic MVCC snapshots, this contains subxact IDs that are in
* progress (and other transactions that are in progress if taken during
* recovery). For historic snapshot it contains *all* xids assigned to the
* replayed transaction, including the toplevel xid.
*
* note: all ids in subxip[] are >= xmin, but we don't bother filtering
* out any that are >= xmax
*/
TransactionId *subxip;
int32 subxcnt; /* # of xact ids in subxip[] */
bool suboverflowed; /* has the subxip array overflowed? */
bool takenDuringRecovery; /* recovery-shaped snapshot? */
bool copied; /* false if it's a static snapshot */
CommandId curcid; /* in my xact, CID < curcid are visible */
/*
* An extra return value for HeapTupleSatisfiesDirty, not used in MVCC
* snapshots.
*/
uint32 speculativeToken;
/*
* Book-keeping information, used by the snapshot manager
*/
uint32 active_count; /* refcount on ActiveSnapshot stack */
uint32 regd_count; /* refcount on RegisteredSnapshots */
pairingheap_node ph_node; /* link in the RegisteredSnapshots heap */
TimestampTz whenTaken; /* timestamp when snapshot was taken */
XLogRecPtr lsn; /* position in the WAL stream when taken */
} SnapshotData;
依賴的函式
1、lfirst_*
/*
* NB: There is an unfortunate legacy from a previous incarnation of
* the List API: the macro lfirst() was used to mean "the data in this
* cons cell". To avoid changing every usage of lfirst(), that meaning
* has been kept. As a result, lfirst() takes a ListCell and returns
* the data it contains; to get the data in the first cell of a
* List, use linitial(). Worse, lsecond() is more closely related to
* linitial() than lfirst(): given a List, lsecond() returns the data
* in the second cons cell.
*/
#define lnext(lc) ((lc)->next)
#define lfirst(lc) ((lc)->data.ptr_value)
#define lfirst_int(lc) ((lc)->data.int_value)
#define lfirst_oid(lc) ((lc)->data.oid_value)
#define lfirst_node(type,lc) castNode(type, lfirst(lc))
/*
* castNode(type, ptr) casts ptr to "type *", and if assertions are enabled,
* verifies that the node has the appropriate type (using its nodeTag()).
*
* Use an inline function when assertions are enabled, to avoid multiple
* evaluations of the ptr argument (which could e.g. be a function call).
*/
#ifdef USE_ASSERT_CHECKING
static inline Node *
castNodeImpl(NodeTag type, void *ptr)
{
Assert(ptr == NULL || nodeTag(ptr) == type);
return (Node *) ptr;
}
#define castNode(_type_, nodeptr) ((_type_ *) castNodeImpl(T_##_type_, nodeptr))
#else
#define castNode(_type_, nodeptr) ((_type_ *) (nodeptr))
#endif /* USE_ASSERT_CHECKING */
2、Snapshot相關
//留待MVCC再行解讀
GetTransactionSnapshot
RegisterSnapshot
PushCopiedSnapshot
UpdateActiveSnapshotCommandId
PopActiveSnapshot
3、ProcessQuery
//上一節已介紹
4、CommandCounterIncrement
/*
* CommandCounterIncrement
*/
void
CommandCounterIncrement(void)
{
/*
* If the current value of the command counter hasn't been "used" to mark
* tuples, we need not increment it, since there's no need to distinguish
* a read-only command from others. This helps postpone command counter
* overflow, and keeps no-op CommandCounterIncrement operations cheap.
*/
if (currentCommandIdUsed)
{
/*
* Workers synchronize transaction state at the beginning of each
* parallel operation, so we can't account for new commands after that
* point.
*/
if (IsInParallelMode() || IsParallelWorker())
elog(ERROR, "cannot start commands during a parallel operation");
currentCommandId += 1;
if (currentCommandId == InvalidCommandId)
{
currentCommandId -= 1;
ereport(ERROR,
(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
errmsg("cannot have more than 2^32-2 commands in a transaction")));
}
currentCommandIdUsed = false;
/* Propagate new command ID into static snapshots */
SnapshotSetCommandId(currentCommandId);
/*
* Make any catalog changes done by the just-completed command visible
* in the local syscache. We obviously don't need to do this after a
* read-only command. (But see hacks in inval.c to make real sure we
* don't think a command that queued inval messages was read-only.)
*/
AtCCI_LocalCache();
}
}
5、MemoryContextDeleteChildren
/*
* MemoryContextDeleteChildren
* Delete all the descendants of the named context and release all
* space allocated therein. The named context itself is not touched.
*/
void
MemoryContextDeleteChildren(MemoryContext context)
{
AssertArg(MemoryContextIsValid(context));
/*
* MemoryContextDelete will delink the child from me, so just iterate as
* long as there is a child.
*/
while (context->firstchild != NULL)
MemoryContextDelete(context->firstchild);
}
二、原始碼解讀
1、PortalRun
/*
* PortalRun
* Run a portal's query or queries.
*
* count <= 0 is interpreted as a no-op: the destination gets started up
* and shut down, but nothing else happens. Also, count == FETCH_ALL is
* interpreted as "all rows". Note that count is ignored in multi-query
* situations, where we always run the portal to completion.
*
* isTopLevel: true if query is being executed at backend "top level"
* (that is, directly from a client command message)
*
* dest: where to send output of primary (canSetTag) query
*
* altdest: where to send output of non-primary queries
*
* completionTag: points to a buffer of size COMPLETION_TAG_BUFSIZE
* in which to store a command completion status string.
* May be NULL if caller doesn't want a status string.
*
* Returns true if the portal's execution is complete, false if it was
* suspended due to exhaustion of the count parameter.
*/
/*
輸入：
參照PortalRunMulti
輸出：
布林變數，成功true，失敗false
*/
bool
PortalRun(Portal portal, long count, bool isTopLevel, bool run_once,
DestReceiver *dest, DestReceiver *altdest,
char *completionTag)
{
bool result;//返回結果
uint64 nprocessed;
ResourceOwner saveTopTransactionResourceOwner;//高層事務資源宿主
MemoryContext saveTopTransactionContext;//記憶體上下文
Portal saveActivePortal;//活動的Portal
ResourceOwner saveResourceOwner;
MemoryContext savePortalContext;
MemoryContext saveMemoryContext;
AssertArg(PortalIsValid(portal));
TRACE_POSTGRESQL_QUERY_EXECUTE_START();
/* Initialize completion tag to empty string */
if (completionTag)
completionTag[0] = '\0';
if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
{
elog(DEBUG3, "PortalRun");
/* PORTAL_MULTI_QUERY logs its own stats per query */
ResetUsage();
}
/*
* Check for improper portal use, and mark portal active.
*/
MarkPortalActive(portal);
/* Set run_once flag. Shouldn't be clear if previously set. */
Assert(!portal->run_once || run_once);
portal->run_once = run_once;
/*
* Set up global portal context pointers.
*
* We have to play a special game here to support utility commands like
* VACUUM and CLUSTER, which internally start and commit transactions.
* When we are called to execute such a command, CurrentResourceOwner will
* be pointing to the TopTransactionResourceOwner --- which will be
* destroyed and replaced in the course of the internal commit and
* restart. So we need to be prepared to restore it as pointing to the
* exit-time TopTransactionResourceOwner. (Ain't that ugly? This idea of
* internally starting whole new transactions is not good.)
* CurrentMemoryContext has a similar problem, but the other pointers we
* save here will be NULL or pointing to longer-lived objects.
*/
//保護現場
saveTopTransactionResourceOwner = TopTransactionResourceOwner;
saveTopTransactionContext = TopTransactionContext;
saveActivePortal = ActivePortal;
saveResourceOwner = CurrentResourceOwner;
savePortalContext = PortalContext;
saveMemoryContext = CurrentMemoryContext;
PG_TRY();
{
ActivePortal = portal;
if (portal->resowner)
CurrentResourceOwner = portal->resowner;
PortalContext = portal->portalContext;
MemoryContextSwitchTo(PortalContext);
switch (portal->strategy)
{
case PORTAL_ONE_SELECT:
case PORTAL_ONE_RETURNING:
case PORTAL_ONE_MOD_WITH:
case PORTAL_UTIL_SELECT:
/*
* If we have not yet run the command, do so, storing its
* results in the portal's tuplestore. But we don't do that
* for the PORTAL_ONE_SELECT case.
*/
if (portal->strategy != PORTAL_ONE_SELECT && !portal->holdStore)
FillPortalStore(portal, isTopLevel);
/*
* Now fetch desired portion of results.
*/
nprocessed = PortalRunSelect(portal, true, count, dest);
/*
* If the portal result contains a command tag and the caller
* gave us a pointer to store it, copy it. Patch the "SELECT"
* tag to also provide the rowcount.
*/
if (completionTag && portal->commandTag)
{
if (strcmp(portal->commandTag, "SELECT") == 0)
snprintf(completionTag, COMPLETION_TAG_BUFSIZE,
"SELECT " UINT64_FORMAT, nprocessed);
else
strcpy(completionTag, portal->commandTag);
}
/* Mark portal not active */
portal->status = PORTAL_READY;
/*
* Since it's a forward fetch, say DONE iff atEnd is now true.
*/
result = portal->atEnd;
break;
case PORTAL_MULTI_QUERY://INSERT語句
PortalRunMulti(portal, isTopLevel, false,
dest, altdest, completionTag);
/* Prevent portal's commands from being re-executed */
MarkPortalDone(portal);
/* Always complete at end of RunMulti */
result = true;
break;
default:
elog(ERROR, "unrecognized portal strategy: %d",
(int) portal->strategy);
result = false; /* keep compiler quiet */
break;
}
}
PG_CATCH();
{
/* Uncaught error while executing portal: mark it dead */
MarkPortalFailed(portal);
/* Restore global vars and propagate error */
if (saveMemoryContext == saveTopTransactionContext)
MemoryContextSwitchTo(TopTransactionContext);
else
MemoryContextSwitchTo(saveMemoryContext);
ActivePortal = saveActivePortal;
if (saveResourceOwner == saveTopTransactionResourceOwner)
CurrentResourceOwner = TopTransactionResourceOwner;
else
CurrentResourceOwner = saveResourceOwner;
PortalContext = savePortalContext;
PG_RE_THROW();
}
PG_END_TRY();
if (saveMemoryContext == saveTopTransactionContext)
MemoryContextSwitchTo(TopTransactionContext);
else
MemoryContextSwitchTo(saveMemoryContext);
ActivePortal = saveActivePortal;
if (saveResourceOwner == saveTopTransactionResourceOwner)
CurrentResourceOwner = TopTransactionResourceOwner;
else
CurrentResourceOwner = saveResourceOwner;
PortalContext = savePortalContext;
if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
ShowUsage("EXECUTOR STATISTICS");
TRACE_POSTGRESQL_QUERY_EXECUTE_DONE();
return result;
}
2、PortalRunMulti
/*
* PortalRunMulti
* Execute a portal's queries in the general case (multi queries
* or non-SELECT-like queries)
*/
/*
輸入：
portal-“門戶”資料結構
isTopLevel-頂層？
setHoldSnapshot-是否持有快照
dest-目標端
altdest-?
completionTag-完成標記（用於語句執行結果輸出）
輸出：
無
*/
static void
PortalRunMulti(Portal portal,
bool isTopLevel, bool setHoldSnapshot,
DestReceiver *dest, DestReceiver *altdest,
char *completionTag)
{
bool active_snapshot_set = false;//活躍snapshot？
ListCell *stmtlist_item;//SQL語句，臨時變數
/*
* If the destination is DestRemoteExecute, change to DestNone. The
* reason is that the client won't be expecting any tuples, and indeed has
* no way to know what they are, since there is no provision for Describe
* to send a RowDescription message when this portal execution strategy is
* in effect. This presently will only affect SELECT commands added to
* non-SELECT queries by rewrite rules: such commands will be executed,
* but the results will be discarded unless you use "simple Query"
* protocol.
*/
if (dest->mydest == DestRemoteExecute)
dest = None_Receiver;
if (altdest->mydest == DestRemoteExecute)
altdest = None_Receiver;
/*
* Loop to handle the individual queries generated from a single parsetree
* by analysis and rewrite.
*/
foreach(stmtlist_item, portal->stmts)//迴圈處理SQL語句
{
PlannedStmt *pstmt = lfirst_node(PlannedStmt, stmtlist_item);//獲取已規劃的語句
/*
* If we got a cancel signal in prior command, quit
*/
CHECK_FOR_INTERRUPTS();
if (pstmt->utilityStmt == NULL)//非“工具類”語句
{
/*
* process a plannable query.
*/
TRACE_POSTGRESQL_QUERY_EXECUTE_START();
if (log_executor_stats)
ResetUsage();
/*
* Must always have a snapshot for plannable queries. First time
* through, take a new snapshot; for subsequent queries in the
* same portal, just update the snapshot's copy of the command
* counter.
*/
if (!active_snapshot_set)
{
Snapshot snapshot = GetTransactionSnapshot();//獲取事務快照
/* If told to, register the snapshot and save in portal */
if (setHoldSnapshot)
{
snapshot = RegisterSnapshot(snapshot);
portal->holdSnapshot = snapshot;
}
/*
* We can't have the holdSnapshot also be the active one,
* because UpdateActiveSnapshotCommandId would complain. So
* force an extra snapshot copy. Plain PushActiveSnapshot
* would have copied the transaction snapshot anyway, so this
* only adds a copy step when setHoldSnapshot is true. (It's
* okay for the command ID of the active snapshot to diverge
* from what holdSnapshot has.)
*/
PushCopiedSnapshot(snapshot);
active_snapshot_set = true;
}
else
UpdateActiveSnapshotCommandId();
//處理查詢
if (pstmt->canSetTag)
{
/* statement can set tag string */
ProcessQuery(pstmt,
portal->sourceText,
portal->portalParams,
portal->queryEnv,
dest, completionTag);
}
else
{
/* stmt added by rewrite cannot set tag */
ProcessQuery(pstmt,
portal->sourceText,
portal->portalParams,
portal->queryEnv,
altdest, NULL);
}
if (log_executor_stats)
ShowUsage("EXECUTOR STATISTICS");
TRACE_POSTGRESQL_QUERY_EXECUTE_DONE();
}
else//“工具類”語句
{
/*
* process utility functions (create, destroy, etc..)
*
* We must not set a snapshot here for utility commands (if one is
* needed, PortalRunUtility will do it). If a utility command is
* alone in a portal then everything's fine. The only case where
* a utility command can be part of a longer list is that rules
* are allowed to include NotifyStmt. NotifyStmt doesn't care
* whether it has a snapshot or not, so we just leave the current
* snapshot alone if we have one.
*/
if (pstmt->canSetTag)
{
Assert(!active_snapshot_set);
/* statement can set tag string */
PortalRunUtility(portal, pstmt, isTopLevel, false,
dest, completionTag);
}
else
{
Assert(IsA(pstmt->utilityStmt, NotifyStmt));
/* stmt added by rewrite cannot set tag */
PortalRunUtility(portal, pstmt, isTopLevel, false,
altdest, NULL);
}
}
/*
* Increment command counter between queries, but not after the last
* one.
*/
if (lnext(stmtlist_item) != NULL)
CommandCounterIncrement();
/*
* Clear subsidiary contexts to recover temporary memory.
*/
Assert(portal->portalContext == CurrentMemoryContext);
MemoryContextDeleteChildren(portal->portalContext);//釋放資源
}
/* Pop the snapshot if we pushed one. */
if (active_snapshot_set)
PopActiveSnapshot();
/*
* If a command completion tag was supplied, use it. Otherwise use the
* portal's commandTag as the default completion tag.
*
* Exception: Clients expect INSERT/UPDATE/DELETE tags to have counts, so
* fake them with zeros. This can happen with DO INSTEAD rules if there
* is no replacement query of the same type as the original. We print "0
* 0" here because technically there is no query of the matching tag type,
* and printing a non-zero count for a different query type seems wrong,
* e.g. an INSERT that does an UPDATE instead should not print "0 1" if
* one row was updated. See QueryRewrite(), step 3, for details.
*/
if (completionTag && completionTag[0] == '\0')//操作提示
{
if (portal->commandTag)
strcpy(completionTag, portal->commandTag);
if (strcmp(completionTag, "SELECT") == 0)
sprintf(completionTag, "SELECT 0 0");
else if (strcmp(completionTag, "INSERT") == 0)
strcpy(completionTag, "INSERT 0 0");
else if (strcmp(completionTag, "UPDATE") == 0)
strcpy(completionTag, "UPDATE 0");
else if (strcmp(completionTag, "DELETE") == 0)
strcpy(completionTag, "DELETE 0");
}
}
三、跟蹤分析
插入測試資料：
testdb=# -- 獲取pid
testdb=# select pg_backend_pid();
pg_backend_pid
----------------
2551
(1 row)
testdb=# -- 插入1行
testdb=# insert into t_insert values(20,'PortalRun','PortalRun','PortalRun');
啟動gdb，跟蹤除錯：
1、PortalRun
[root@localhost ~]# gdb -p 2551
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-100.el7
Copyright (C) 2013 Free Software Foundation, Inc.
...
(gdb) b PortalRun
Breakpoint 1 at 0x8528af: file pquery.c, line 707.
(gdb) c
Continuing.
Breakpoint 1, PortalRun (portal=0x2c6f490, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x2ccb4d8, altdest=0x2ccb4d8, completionTag=0x7ffe94ba4940 "") at pquery.c:707
707 if (completionTag)
#檢視輸入引數
#1、portal
(gdb) p *portal
$1 = {name = 0x2c72e98 "", prepStmtName = 0x0, portalContext = 0x2cc1470, resowner = 0x2c3ad10, cleanup = 0x62f15c <PortalCleanup>, createSubid = 1, activeSubid = 1,
sourceText = 0x2c09ef0 "insert into t_insert values(20,'PortalRun','PortalRun','PortalRun');", commandTag = 0xb50908 "INSERT", stmts = 0x2ccb4a8, cplan = 0x0, portalParams = 0x0, queryEnv = 0x0,
strategy = PORTAL_MULTI_QUERY, cursorOptions = 4, run_once = false, status = PORTAL_READY, portalPinned = false, autoHeld = false, queryDesc = 0x0, tupDesc = 0x0, formats = 0x0, holdStore = 0x0,
holdContext = 0x0, holdSnapshot = 0x0, atStart = true, atEnd = true, portalPos = 0, creation_time = 587033564125509, visible = false}
(gdb) p *(portal->portalContext)
$2 = {type = T_AllocSetContext, isReset = true, allowInCritSection = false, methods = 0xb8c720 <AllocSetMethods>, parent = 0x2c6f380, firstchild = 0x0, prevchild = 0x0, nextchild = 0x0,
name = 0xb8d2f1 "PortalContext", ident = 0x2c72e98 "", reset_cbs = 0x0}
(gdb) p *(portal->resowner)
$3 = {parent = 0x2c35518, firstchild = 0x0, nextchild = 0x0, name = 0xb8d2ff "Portal", bufferarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, catrefarr = {
itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, catlistrefarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0},
relrefarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, planrefarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0},
tupdescarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, snapshotarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0,
lastidx = 0}, filearr = {itemsarr = 0x0, invalidval = 18446744073709551615, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, dsmarr = {itemsarr = 0x0, invalidval = 0, capacity = 0,
nitems = 0, maxitems = 0, lastidx = 0}, jitarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, nlocks = 0, locks = {0x0 <repeats 15 times>}}
(gdb) p *(portal->resowner->parent)
$4 = {parent = 0x0, firstchild = 0x2c3ad10, nextchild = 0x0, name = 0xa1b515 "TopTransaction", bufferarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0},
catrefarr = {itemsarr = 0x2c3b040, invalidval = 0, capacity = 16, nitems = 0, maxitems = 16, lastidx = 4294967295}, catlistrefarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0,
maxitems = 0, lastidx = 0}, relrefarr = {itemsarr = 0x2c35728, invalidval = 0, capacity = 16, nitems = 0, maxitems = 16, lastidx = 4294967295}, planrefarr = {itemsarr = 0x0, invalidval = 0,
capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, tupdescarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, snapshotarr = {itemsarr = 0x0,
invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, filearr = {itemsarr = 0x0, invalidval = 18446744073709551615, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, dsmarr = {
itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, jitarr = {itemsarr = 0x0, invalidval = 0, capacity = 0, nitems = 0, maxitems = 0, lastidx = 0}, nlocks = 1,
locks = {0x2c28320, 0x0 <repeats 14 times>}}
#2、count
(gdb) p count
$5 = 9223372036854775807
#3、isTopLevel
(gdb) p isTopLevel
$6 = true
#4、run_once
(gdb) p run_once
$7 = true
#5、dest
$8 = (DestReceiver *) 0x2ccb4d8
(gdb) p *dest
$9 = {receiveSlot = 0x4857ad <printtup>, rStartup = 0x485196 <printtup_startup>, rShutdown = 0x485bad <printtup_shutdown>, rDestroy = 0x485c21 <printtup_destroy>, mydest = DestRemote}
(gdb)
#6、altdest
(gdb) p altdest
$10 = (DestReceiver *) 0x2ccb4d8
(gdb) p *altdest
$11 = {receiveSlot = 0x4857ad <printtup>, rStartup = 0x485196 <printtup_startup>, rShutdown = 0x485bad <printtup_shutdown>, rDestroy = 0x485c21 <printtup_destroy>, mydest = DestRemote}
(gdb)
#7、completionTag
(gdb) p completionTag
$12 = 0x7ffe94ba4940 ""
#單步除錯
710 if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
(gdb)
720 MarkPortalActive(portal);
(gdb)
724 portal->run_once = run_once;
(gdb)
740 saveTopTransactionResourceOwner = TopTransactionResourceOwner;
(gdb)
741 saveTopTransactionContext = TopTransactionContext;
(gdb)
742 saveActivePortal = ActivePortal;
(gdb)
743 saveResourceOwner = CurrentResourceOwner;
(gdb)
744 savePortalContext = PortalContext;
(gdb)
745 saveMemoryContext = CurrentMemoryContext;
(gdb)
746 PG_TRY();
(gdb)
748 ActivePortal = portal;
(gdb)
749 if (portal->resowner)
(gdb)
750 CurrentResourceOwner = portal->resowner;
(gdb)
751 PortalContext = portal->portalContext;
(gdb)
753 MemoryContextSwitchTo(PortalContext);
(gdb)
755 switch (portal->strategy)
(gdb) p portal->strategy
$13 = PORTAL_MULTI_QUERY
(gdb) next
799 PortalRunMulti(portal, isTopLevel, false,
(gdb)
803 MarkPortalDone(portal);
(gdb)
806 result = true;
(gdb)
807 break;
(gdb)
835 PG_END_TRY();
(gdb)
837 if (saveMemoryContext == saveTopTransactionContext)
(gdb)
838 MemoryContextSwitchTo(TopTransactionContext);
(gdb)
841 ActivePortal = saveActivePortal;
(gdb)
842 if (saveResourceOwner == saveTopTransactionResourceOwner)
(gdb)
843 CurrentResourceOwner = TopTransactionResourceOwner;
(gdb)
846 PortalContext = savePortalContext;
(gdb)
848 if (log_executor_stats && portal->strategy != PORTAL_MULTI_QUERY)
(gdb)
853 return result;
(gdb)
854 }
#DONE!
2、PortalRunMulti
(gdb) b PortalRunMulti
Breakpoint 1 at 0x8533df: file pquery.c, line 1210.
(gdb) c
Continuing.
Breakpoint 1, PortalRunMulti (portal=0x2c6f490, isTopLevel=true, setHoldSnapshot=false, dest=0x2cbe8f8, altdest=0x2cbe8f8, completionTag=0x7ffe94ba4940 "") at pquery.c:1210
1210 bool active_snapshot_set = false;
#輸入引數
#1、portal
(gdb) p *portal
$1 = {name = 0x2c72e98 "", prepStmtName = 0x0, portalContext = 0x2c2d3d0, resowner = 0x2c3ad10, cleanup = 0x62f15c <PortalCleanup>, createSubid = 1, activeSubid = 1,
sourceText = 0x2c09ef0 "insert into t_insert values(21,'PortalRunMulti','PortalRunMulti','PortalRunMulti');", commandTag = 0xb50908 "INSERT", stmts = 0x2cbe8c8, cplan = 0x0, portalParams = 0x0,
queryEnv = 0x0, strategy = PORTAL_MULTI_QUERY, cursorOptions = 4, run_once = true, status = PORTAL_ACTIVE, portalPinned = false, autoHeld = false, queryDesc = 0x0, tupDesc = 0x0, formats = 0x0,
holdStore = 0x0, holdContext = 0x0, holdSnapshot = 0x0, atStart = true, atEnd = true, portalPos = 0, creation_time = 587034112962796, visible = false}
(gdb) p *(portal->portalContext)
$2 = {type = T_AllocSetContext, isReset = true, allowInCritSection = false, methods = 0xb8c720 <AllocSetMethods>, parent = 0x2c6f380, firstchild = 0x0, prevchild = 0x0, nextchild = 0x0,
name = 0xb8d2f1 "PortalContext", ident = 0x2c72e98 "", reset_cbs = 0x0}
#2、isTopLevel
(gdb) p isTopLevel
$3 = true
#3、setHoldSnapshot
(gdb) p setHoldSnapshot
$4 = false
#4、dest
(gdb) p *dest
$5 = {receiveSlot = 0x4857ad <printtup>, rStartup = 0x485196 <printtup_startup>, rShutdown = 0x485bad <printtup_shutdown>, rDestroy = 0x485c21 <printtup_destroy>, mydest = DestRemote}
#5、altdest
(gdb) p *altdest
$6 = {receiveSlot = 0x4857ad <printtup>, rStartup = 0x485196 <printtup_startup>, rShutdown = 0x485bad <printtup_shutdown>, rDestroy = 0x485c21 <printtup_destroy>, mydest = DestRemote}
#6、completionTag
(gdb) p *completionTag
$7 = 0 '\000'
#單步除錯
...
(gdb) next
1234 PlannedStmt *pstmt = lfirst_node(PlannedStmt, stmtlist_item);
(gdb)
1239 CHECK_FOR_INTERRUPTS();
(gdb) p *pstmt
$12 = {type = T_PlannedStmt, commandType = CMD_INSERT, queryId = 0, hasReturning = false, hasModifyingCTE = false, canSetTag = true, transientPlan = false, dependsOnRole = false,
parallelModeNeeded = false, jitFlags = 0, planTree = 0x2c0aff8, rtable = 0x2cbe7d8, resultRelations = 0x2cbe878, nonleafResultRelations = 0x0, rootResultRelations = 0x0, subplans = 0x0,
rewindPlanIDs = 0x0, rowMarks = 0x0, relationOids = 0x2cbe828, invalItems = 0x0, paramExecTypes = 0x2c31700, utilityStmt = 0x0, stmt_location = 0, stmt_len = 82}
(gdb) next
1241 if (pstmt->utilityStmt == NULL)
(gdb)
1248 if (log_executor_stats)
(gdb)
1257 if (!active_snapshot_set)
(gdb)
1259 Snapshot snapshot = GetTransactionSnapshot();
(gdb)
1262 if (setHoldSnapshot)
(gdb) p *snapshot
$13 = {satisfies = 0x9f73fc <HeapTupleSatisfiesMVCC>, xmin = 1612887, xmax = 1612887, xip = 0x2c2d1c0, xcnt = 0, subxip = 0x2c81c70, subxcnt = 0, suboverflowed = false, takenDuringRecovery = false,
copied = false, curcid = 0, speculativeToken = 0, active_count = 0, regd_count = 0, ph_node = {first_child = 0x0, next_sibling = 0x0, prev_or_parent = 0x0}, whenTaken = 0, lsn = 0}
(gdb)
...
(gdb)
PortalRun (portal=0x2c6f490, count=9223372036854775807, isTopLevel=true, run_once=true, dest=0x2cbe8f8, altdest=0x2cbe8f8, completionTag=0x7ffe94ba4940 "INSERT 0 1") at pquery.c:803
803 MarkPortalDone(portal);
#DONE!
四、小結
1、Portal：門戶，類似設計模式中的Facade，對外的統一介面。該資料結構如何構造，有待接下來的上層函式解讀。
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/6906/viewspace-2374905/，如需轉載，請註明出處，否則將追究法律責任。
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