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Revalidation of a plancache entry (after a cache invalidation event) requires acquiring a snapshot. Normally that is harmless, but not if the cached statement is one that needs to run without acquiring a snapshot. We were already aware of that for TransactionStmts, but for some reason hadn't extrapolated to the other statements that PlannedStmtRequiresSnapshot() knows mustn't set a snapshot. This can lead to unexpected failures of commands such as SET TRANSACTION ISOLATION LEVEL. We can fix it in the same way, by excluding those command types from revalidation. However, we can do even better than that: there is no need to revalidate for any statement type for which parse analysis, rewrite, and plan steps do nothing interesting, which is nearly all utility commands. To mechanize this, invent a parser function stmt_requires_parse_analysis() that tells whether parse analysis does anything beyond wrapping a CMD_UTILITY Query around the raw parse tree. If that's what it does, then rewrite and plan will just skip the Query, so that it is not possible for the same raw parse tree to produce a different plan tree after cache invalidation. stmt_requires_parse_analysis() is basically equivalent to the existing function analyze_requires_snapshot(), except that for obscure reasons that function omits ReturnStmt and CallStmt. It is unclear whether those were oversights or intentional. I have not been able to demonstrate a bug from not acquiring a snapshot while analyzing these commands, but at best it seems mighty fragile. It seems safer to acquire a snapshot for parse analysis of these commands too, which allows making stmt_requires_parse_analysis and analyze_requires_snapshot equivalent. In passing this fixes a second bug, which is that ResetPlanCache would exclude ReturnStmts and CallStmts from revalidation. That's surely *not* safe, since they contain parsable expressions. Per bug #18059 from Pavel Kulakov. Back-patch to all supported branches. Discussion: https://postgr.es/m/18059-79c692f036b25346@postgresql.org
64 lines
2.5 KiB
C
64 lines
2.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* analyze.h
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* parse analysis for optimizable statements
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*
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*
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* Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/parser/analyze.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef ANALYZE_H
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#define ANALYZE_H
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#include "nodes/params.h"
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#include "parser/parse_node.h"
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#include "utils/queryjumble.h"
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/* Hook for plugins to get control at end of parse analysis */
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typedef void (*post_parse_analyze_hook_type) (ParseState *pstate,
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Query *query,
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JumbleState *jstate);
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extern PGDLLIMPORT post_parse_analyze_hook_type post_parse_analyze_hook;
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extern Query *parse_analyze_fixedparams(RawStmt *parseTree, const char *sourceText,
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const Oid *paramTypes, int numParams, QueryEnvironment *queryEnv);
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extern Query *parse_analyze_varparams(RawStmt *parseTree, const char *sourceText,
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Oid **paramTypes, int *numParams, QueryEnvironment *queryEnv);
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extern Query *parse_analyze_withcb(RawStmt *parseTree, const char *sourceText,
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ParserSetupHook parserSetup,
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void *parserSetupArg,
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QueryEnvironment *queryEnv);
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extern Query *parse_sub_analyze(Node *parseTree, ParseState *parentParseState,
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CommonTableExpr *parentCTE,
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bool locked_from_parent,
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bool resolve_unknowns);
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extern List *transformInsertRow(ParseState *pstate, List *exprlist,
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List *stmtcols, List *icolumns, List *attrnos,
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bool strip_indirection);
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extern List *transformUpdateTargetList(ParseState *pstate,
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List *targetList);
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extern Query *transformTopLevelStmt(ParseState *pstate, RawStmt *parseTree);
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extern Query *transformStmt(ParseState *pstate, Node *parseTree);
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extern bool stmt_requires_parse_analysis(RawStmt *parseTree);
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extern bool analyze_requires_snapshot(RawStmt *parseTree);
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extern const char *LCS_asString(LockClauseStrength strength);
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extern void CheckSelectLocking(Query *qry, LockClauseStrength strength);
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extern void applyLockingClause(Query *qry, Index rtindex,
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LockClauseStrength strength,
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LockWaitPolicy waitPolicy, bool pushedDown);
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extern List *BuildOnConflictExcludedTargetlist(Relation targetrel,
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Index exclRelIndex);
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extern SortGroupClause *makeSortGroupClauseForSetOp(Oid rescoltype, bool require_hash);
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#endif /* ANALYZE_H */
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