From 43a0a3638eb005e2df32c54a212811f16ed7cfe2 Mon Sep 17 00:00:00 2001 From: "okbob@github.com" Date: Sun, 28 Jan 2024 20:54:20 +0100 Subject: [PATCH 04/19] DISCARD VARIABLES Implementation of DISCARD VARIABLES commands by removing hash table with session variables and resetting related memory context. --- doc/src/sgml/ref/discard.sgml | 13 +++- src/backend/commands/discard.c | 6 ++ src/backend/commands/session_variable.c | 28 ++++++++- src/backend/parser/gram.y | 6 ++ src/backend/tcop/utility.c | 3 + src/bin/psql/tab-complete.c | 2 +- src/include/commands/session_variable.h | 2 + src/include/nodes/parsenodes.h | 1 + src/include/tcop/cmdtaglist.h | 1 + .../regress/expected/session_variables.out | 62 +++++++++++++++++++ src/test/regress/sql/session_variables.sql | 36 +++++++++++ 11 files changed, 157 insertions(+), 3 deletions(-) diff --git a/doc/src/sgml/ref/discard.sgml b/doc/src/sgml/ref/discard.sgml index bf44c523ca..61b967f9c9 100644 --- a/doc/src/sgml/ref/discard.sgml +++ b/doc/src/sgml/ref/discard.sgml @@ -21,7 +21,7 @@ PostgreSQL documentation -DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP } +DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP | VARIABLES } @@ -66,6 +66,16 @@ DISCARD { ALL | PLANS | SEQUENCES | TEMPORARY | TEMP } + + VARIABLES + + + Resets the value of all session variables. If a variable + is later reused, it is re-initialized to NULL. + + + + TEMPORARY or TEMP @@ -93,6 +103,7 @@ SELECT pg_advisory_unlock_all(); DISCARD PLANS; DISCARD TEMP; DISCARD SEQUENCES; +DISCARD VARIABLES; diff --git a/src/backend/commands/discard.c b/src/backend/commands/discard.c index 92d983ac74..d06ebaba6f 100644 --- a/src/backend/commands/discard.c +++ b/src/backend/commands/discard.c @@ -18,6 +18,7 @@ #include "commands/async.h" #include "commands/discard.h" #include "commands/prepare.h" +#include "commands/session_variable.h" #include "commands/sequence.h" #include "utils/guc.h" #include "utils/portal.h" @@ -48,6 +49,10 @@ DiscardCommand(DiscardStmt *stmt, bool isTopLevel) ResetTempTableNamespace(); break; + case DISCARD_VARIABLES: + ResetSessionVariables(); + break; + default: elog(ERROR, "unrecognized DISCARD target: %d", stmt->target); } @@ -75,4 +80,5 @@ DiscardAll(bool isTopLevel) ResetPlanCache(); ResetTempTableNamespace(); ResetSequenceCaches(); + ResetSessionVariables(); } diff --git a/src/backend/commands/session_variable.c b/src/backend/commands/session_variable.c index c8ddefc20e..c796858712 100644 --- a/src/backend/commands/session_variable.c +++ b/src/backend/commands/session_variable.c @@ -102,7 +102,13 @@ pg_variable_cache_callback(Datum arg, int cacheid, uint32 hashvalue) elog(DEBUG1, "pg_variable_cache_callback %u %u", cacheid, hashvalue); - Assert(sessionvars); + /* + * There is no guarantee of sessionvars being initialized, even when + * receiving an invalidation callback, as DISCARD [ ALL | VARIABLES ] + * destroys the hash table entirely. + */ + if (!sessionvars) + return; /* * When the hashvalue is not specified, then we have to recheck all @@ -702,3 +708,23 @@ pg_session_variables(PG_FUNCTION_ARGS) return (Datum) 0; } + +/* + * Fast drop of the complete content of all session variables hash table, and + * cleanup of any list that wouldn't be relevant anymore. + * This is used by DISCARD VARIABLES (and DISCARD ALL) command. + */ +void +ResetSessionVariables(void) +{ + /* Destroy hash table and reset related memory context */ + if (sessionvars) + { + hash_destroy(sessionvars); + sessionvars = NULL; + } + + /* Release memory allocated by session variables */ + if (SVariableMemoryContext != NULL) + MemoryContextReset(SVariableMemoryContext); +} diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y index 4cba30f36d..244b7e9681 100644 --- a/src/backend/parser/gram.y +++ b/src/backend/parser/gram.y @@ -2074,7 +2074,13 @@ DiscardStmt: n->target = DISCARD_SEQUENCES; $$ = (Node *) n; } + | DISCARD VARIABLES + { + DiscardStmt *n = makeNode(DiscardStmt); + n->target = DISCARD_VARIABLES; + $$ = (Node *) n; + } ; diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c index 662dbcd1dd..db6004a05c 100644 --- a/src/backend/tcop/utility.c +++ b/src/backend/tcop/utility.c @@ -2959,6 +2959,9 @@ CreateCommandTag(Node *parsetree) case DISCARD_SEQUENCES: tag = CMDTAG_DISCARD_SEQUENCES; break; + case DISCARD_VARIABLES: + tag = CMDTAG_DISCARD_VARIABLES; + break; default: tag = CMDTAG_UNKNOWN; } diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c index 7e06a37303..1100ebcab8 100644 --- a/src/bin/psql/tab-complete.c +++ b/src/bin/psql/tab-complete.c @@ -3740,7 +3740,7 @@ psql_completion(const char *text, int start, int end) /* DISCARD */ else if (Matches("DISCARD")) - COMPLETE_WITH("ALL", "PLANS", "SEQUENCES", "TEMP"); + COMPLETE_WITH("ALL", "PLANS", "SEQUENCES", "TEMP", "VARIABLES"); /* DO */ else if (Matches("DO")) diff --git a/src/include/commands/session_variable.h b/src/include/commands/session_variable.h index b3f03c6582..443afbafd4 100644 --- a/src/include/commands/session_variable.h +++ b/src/include/commands/session_variable.h @@ -29,4 +29,6 @@ extern Datum GetSessionVariableWithTypeCheck(Oid varid, bool *isNull, Oid expect extern void ExecuteLetStmt(ParseState *pstate, LetStmt *stmt, ParamListInfo params, QueryEnvironment *queryEnv, QueryCompletion *qc); +extern void ResetSessionVariables(void); + #endif diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h index f5020a8a27..713afba8db 100644 --- a/src/include/nodes/parsenodes.h +++ b/src/include/nodes/parsenodes.h @@ -3965,6 +3965,7 @@ typedef enum DiscardMode DISCARD_PLANS, DISCARD_SEQUENCES, DISCARD_TEMP, + DISCARD_VARIABLES, } DiscardMode; typedef struct DiscardStmt diff --git a/src/include/tcop/cmdtaglist.h b/src/include/tcop/cmdtaglist.h index a921af2486..bd7964aea6 100644 --- a/src/include/tcop/cmdtaglist.h +++ b/src/include/tcop/cmdtaglist.h @@ -135,6 +135,7 @@ PG_CMDTAG(CMDTAG_DISCARD_ALL, "DISCARD ALL", false, false, false) PG_CMDTAG(CMDTAG_DISCARD_PLANS, "DISCARD PLANS", false, false, false) PG_CMDTAG(CMDTAG_DISCARD_SEQUENCES, "DISCARD SEQUENCES", false, false, false) PG_CMDTAG(CMDTAG_DISCARD_TEMP, "DISCARD TEMP", false, false, false) +PG_CMDTAG(CMDTAG_DISCARD_VARIABLES, "DISCARD VARIABLES", false, false, false) PG_CMDTAG(CMDTAG_DO, "DO", false, false, false) PG_CMDTAG(CMDTAG_DROP_ACCESS_METHOD, "DROP ACCESS METHOD", true, false, false) PG_CMDTAG(CMDTAG_DROP_AGGREGATE, "DROP AGGREGATE", true, false, false) diff --git a/src/test/regress/expected/session_variables.out b/src/test/regress/expected/session_variables.out index e0d5ac12ab..637402e52c 100644 --- a/src/test/regress/expected/session_variables.out +++ b/src/test/regress/expected/session_variables.out @@ -942,3 +942,65 @@ DROP VARIABLE :"DBNAME".:"DBNAME".b; DROP VARIABLE :"DBNAME".:"DBNAME".:"DBNAME"; DROP SCHEMA :"DBNAME"; RESET search_path; +-- memory cleaning by DISCARD command +CREATE VARIABLE var1 AS varchar; +LET var1 = 'Hello'; +SELECT var1; + var1 +------- + Hello +(1 row) + +DISCARD ALL; +SELECT var1; + var1 +------ + +(1 row) + +LET var1 = 'AHOJ'; +SELECT var1; + var1 +------ + AHOJ +(1 row) + +DISCARD VARIABLES; +SELECT var1; + var1 +------ + +(1 row) + +DROP VARIABLE var1; +-- initial test of debug pg_session_variables function +-- should be zero now +DISCARD VARIABLES; +SELECT count(*) FROM pg_session_variables(); + count +------- + 0 +(1 row) + +CREATE VARIABLE var1 AS varchar; +-- should be zero still +SELECT count(*) FROM pg_session_variables(); + count +------- + 0 +(1 row) + +LET var1 = 'AHOJ'; +SELECT name, typname, can_select, can_update FROM pg_session_variables(); + name | typname | can_select | can_update +------+-------------------+------------+------------ + var1 | character varying | t | t +(1 row) + +DISCARD VARIABLES; +-- should be zero again +SELECT count(*) FROM pg_session_variables(); + count +------- + 0 +(1 row) diff --git a/src/test/regress/sql/session_variables.sql b/src/test/regress/sql/session_variables.sql index 1f72b405a2..3f0c8ef4e8 100644 --- a/src/test/regress/sql/session_variables.sql +++ b/src/test/regress/sql/session_variables.sql @@ -663,3 +663,39 @@ DROP VARIABLE :"DBNAME".:"DBNAME".:"DBNAME"; DROP SCHEMA :"DBNAME"; RESET search_path; + +-- memory cleaning by DISCARD command +CREATE VARIABLE var1 AS varchar; +LET var1 = 'Hello'; +SELECT var1; + +DISCARD ALL; +SELECT var1; + +LET var1 = 'AHOJ'; +SELECT var1; + +DISCARD VARIABLES; +SELECT var1; + +DROP VARIABLE var1; + +-- initial test of debug pg_session_variables function +-- should be zero now +DISCARD VARIABLES; + +SELECT count(*) FROM pg_session_variables(); + +CREATE VARIABLE var1 AS varchar; + +-- should be zero still +SELECT count(*) FROM pg_session_variables(); + +LET var1 = 'AHOJ'; + +SELECT name, typname, can_select, can_update FROM pg_session_variables(); + +DISCARD VARIABLES; + +-- should be zero again +SELECT count(*) FROM pg_session_variables(); -- 2.45.1