Fix SQL function execution to be safe with long-lived FmgrInfos.
fmgr_sql had been designed on the assumption that the FmgrInfo it's called with has only query lifespan. This is demonstrably unsafe in connection with range types, as shown in bug #7881 from Andrew Gierth. Fix things so that we re-generate the function's cache data if the (sub)transaction it was made in is no longer active. Back-patch to 9.2. This might be needed further back, but it's not clear whether the case can realistically arise without range types, so for now I'll desist from back-patching further.
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@ -570,6 +570,27 @@ GetCurrentSubTransactionId(void)
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return s->subTransactionId;
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}
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/*
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* SubTransactionIsActive
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*
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* Test if the specified subxact ID is still active. Note caller is
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* responsible for checking whether this ID is relevant to the current xact.
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*/
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bool
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SubTransactionIsActive(SubTransactionId subxid)
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{
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TransactionState s;
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for (s = CurrentTransactionState; s != NULL; s = s->parent)
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{
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if (s->state == TRANS_ABORT)
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continue;
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if (s->subTransactionId == subxid)
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return true;
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}
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return false;
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}
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/*
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* GetCurrentCommandId
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@ -25,10 +25,12 @@
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#include "nodes/nodeFuncs.h"
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#include "parser/parse_coerce.h"
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#include "parser/parse_func.h"
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#include "storage/proc.h"
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#include "tcop/utility.h"
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#include "utils/builtins.h"
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#include "utils/datum.h"
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#include "utils/lsyscache.h"
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#include "utils/memutils.h"
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#include "utils/snapmgr.h"
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#include "utils/syscache.h"
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@ -74,8 +76,17 @@ typedef struct execution_state
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* and linked to from the fn_extra field of the FmgrInfo struct.
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*
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* Note that currently this has only the lifespan of the calling query.
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* Someday we might want to consider caching the parse/plan results longer
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* than that.
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* Someday we should rewrite this code to use plancache.c to save parse/plan
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* results for longer than that.
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*
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* Physically, though, the data has the lifespan of the FmgrInfo that's used
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* to call the function, and there are cases (particularly with indexes)
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* where the FmgrInfo might survive across transactions. We cannot assume
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* that the parse/plan trees are good for longer than the (sub)transaction in
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* which parsing was done, so we must mark the record with the LXID/subxid of
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* its creation time, and regenerate everything if that's obsolete. To avoid
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* memory leakage when we do have to regenerate things, all the data is kept
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* in a sub-context of the FmgrInfo's fn_mcxt.
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*/
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typedef struct
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{
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@ -106,6 +117,12 @@ typedef struct
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* track of where the original query boundaries are.
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*/
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List *func_state;
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MemoryContext fcontext; /* memory context holding this struct and all
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* subsidiary data */
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LocalTransactionId lxid; /* lxid in which cache was made */
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SubTransactionId subxid; /* subxid in which cache was made */
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} SQLFunctionCache;
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typedef SQLFunctionCache *SQLFunctionCachePtr;
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@ -551,6 +568,8 @@ static void
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init_sql_fcache(FmgrInfo *finfo, Oid collation, bool lazyEvalOK)
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{
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Oid foid = finfo->fn_oid;
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MemoryContext fcontext;
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MemoryContext oldcontext;
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Oid rettype;
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HeapTuple procedureTuple;
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Form_pg_proc procedureStruct;
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@ -562,7 +581,25 @@ init_sql_fcache(FmgrInfo *finfo, Oid collation, bool lazyEvalOK)
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Datum tmp;
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bool isNull;
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/*
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* Create memory context that holds all the SQLFunctionCache data. It
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* must be a child of whatever context holds the FmgrInfo.
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*/
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fcontext = AllocSetContextCreate(finfo->fn_mcxt,
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"SQL function data",
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ALLOCSET_DEFAULT_MINSIZE,
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ALLOCSET_DEFAULT_INITSIZE,
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ALLOCSET_DEFAULT_MAXSIZE);
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oldcontext = MemoryContextSwitchTo(fcontext);
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/*
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* Create the struct proper, link it to fcontext and fn_extra. Once this
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* is done, we'll be able to recover the memory after failure, even if the
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* FmgrInfo is long-lived.
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*/
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fcache = (SQLFunctionCachePtr) palloc0(sizeof(SQLFunctionCache));
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fcache->fcontext = fcontext;
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finfo->fn_extra = (void *) fcache;
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/*
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@ -635,6 +672,11 @@ init_sql_fcache(FmgrInfo *finfo, Oid collation, bool lazyEvalOK)
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* sublist, for example if the last query rewrites to DO INSTEAD NOTHING.
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* (It might not be unreasonable to throw an error in such a case, but
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* this is the historical behavior and it doesn't seem worth changing.)
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*
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* Note: since parsing and planning is done in fcontext, we will generate
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* a lot of cruft that lives as long as the fcache does. This is annoying
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* but we'll not worry about it until the module is rewritten to use
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* plancache.c.
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*/
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raw_parsetree_list = pg_parse_query(fcache->src);
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@ -700,7 +742,13 @@ init_sql_fcache(FmgrInfo *finfo, Oid collation, bool lazyEvalOK)
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fcache,
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lazyEvalOK);
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/* Mark fcache with time of creation to show it's valid */
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fcache->lxid = MyProc->lxid;
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fcache->subxid = GetCurrentSubTransactionId();
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ReleaseSysCache(procedureTuple);
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MemoryContextSwitchTo(oldcontext);
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}
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/* Start up execution of one execution_state node */
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@ -923,9 +971,9 @@ postquel_get_single_result(TupleTableSlot *slot,
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Datum
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fmgr_sql(PG_FUNCTION_ARGS)
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{
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MemoryContext oldcontext;
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SQLFunctionCachePtr fcache;
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ErrorContextCallback sqlerrcontext;
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MemoryContext oldcontext;
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bool randomAccess;
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bool lazyEvalOK;
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bool is_first;
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@ -936,13 +984,6 @@ fmgr_sql(PG_FUNCTION_ARGS)
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List *eslist;
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ListCell *eslc;
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/*
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* Switch to context in which the fcache lives. This ensures that
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* parsetrees, plans, etc, will have sufficient lifetime. The
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* sub-executor is responsible for deleting per-tuple information.
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*/
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oldcontext = MemoryContextSwitchTo(fcinfo->flinfo->fn_mcxt);
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/*
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* Setup error traceback support for ereport()
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*/
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@ -978,20 +1019,43 @@ fmgr_sql(PG_FUNCTION_ARGS)
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}
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/*
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* Initialize fcache (build plans) if first time through.
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* Initialize fcache (build plans) if first time through; or re-initialize
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* if the cache is stale.
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*/
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fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;
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if (fcache != NULL)
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{
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if (fcache->lxid != MyProc->lxid ||
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!SubTransactionIsActive(fcache->subxid))
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{
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/* It's stale; unlink and delete */
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fcinfo->flinfo->fn_extra = NULL;
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MemoryContextDelete(fcache->fcontext);
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fcache = NULL;
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}
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}
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if (fcache == NULL)
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{
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init_sql_fcache(fcinfo->flinfo, PG_GET_COLLATION(), lazyEvalOK);
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fcache = (SQLFunctionCachePtr) fcinfo->flinfo->fn_extra;
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}
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eslist = fcache->func_state;
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/*
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* Switch to context in which the fcache lives. This ensures that our
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* tuplestore etc will have sufficient lifetime. The sub-executor is
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* responsible for deleting per-tuple information. (XXX in the case of a
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* long-lived FmgrInfo, this policy represents more memory leakage, but
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* it's not entirely clear where to keep stuff instead.)
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*/
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oldcontext = MemoryContextSwitchTo(fcache->fcontext);
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/*
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* Find first unfinished query in function, and note whether it's the
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* first query.
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*/
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eslist = fcache->func_state;
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es = NULL;
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is_first = true;
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foreach(eslc, eslist)
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@ -215,6 +215,7 @@ extern TransactionId GetCurrentTransactionId(void);
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extern TransactionId GetCurrentTransactionIdIfAny(void);
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extern TransactionId GetStableLatestTransactionId(void);
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extern SubTransactionId GetCurrentSubTransactionId(void);
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extern bool SubTransactionIsActive(SubTransactionId subxid);
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extern CommandId GetCurrentCommandId(bool used);
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extern TimestampTz GetCurrentTransactionStartTimestamp(void);
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extern TimestampTz GetCurrentStatementStartTimestamp(void);
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