From 725bca72e5d6ade0dbd29dfcf566a25be97de903 Mon Sep 17 00:00:00 2001 From: Craig Ringer Date: Mon, 23 Jan 2017 13:34:02 +0800 Subject: [PATCH 2/2] Introduce txid_status(bigint) to get status of an xact If an application loses its connection while a COMMIT request is in flight, the backend crashes mid-commit, etc, then an application may not be sure whether or not a commit completed successfully or was rolled back. While two-phase commit solves this it does so at a considerable overhead, so introduce a lighter alternative. txid_status(bigint) lets an application determine the status of a a commit based on an xid-with-epoch as returned by txid_current() or similar. Status may be committed, aborted, in-progress (including prepared xacts) or null if the xact is too old for its commit status to still be retained because it has passed the wrap-around epoch boundary. Applications must call txid_current() in their transactions to make much use of this since PostgreSQL does not automatically report an xid to the client when one is assigned. Introduces TransactionIdInRecentPast(...) for the use of other functions that need similar logic in future. Authors: Craig Ringer, Robert Haas --- doc/src/sgml/func.sgml | 27 ++++++ src/backend/utils/adt/txid.c | 116 ++++++++++++++++++++++++++ src/include/catalog/pg_proc.h | 2 + src/include/utils/builtins.h | 164 +++++++++++++++++++++++++++++++++++++ src/test/regress/expected/txid.out | 68 +++++++++++++++ src/test/regress/sql/txid.sql | 38 +++++++++ 6 files changed, 415 insertions(+) diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index b214218..0095915 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -17190,6 +17190,10 @@ SELECT collation for ('foo' COLLATE "de_DE"); txid_visible_in_snapshot + + txid_status + + The functions shown in provide server transaction information in an exportable form. The main @@ -17240,6 +17244,11 @@ SELECT collation for ('foo' COLLATE "de_DE"); boolean is transaction ID visible in snapshot? (do not use with subtransaction ids) + + txid_status(bigint) + txid_status + report the status of the given xact - committed, aborted, in progress, or NULL if the xid is too old + @@ -17310,6 +17319,24 @@ SELECT collation for ('foo' COLLATE "de_DE"); + txid_status(bigint) reports the commit status of a recent + transaction. Applications may use it to determine whether a transaction + committed or aborted when the application and database server become + disconnected while a COMMIT is in progress. + The status of a transaction will be reported as either + in progress, + committed, or aborted, provided that the + transaction is recent enough that the system retains the commit status + of that transaction. If is old enough that no references to that + transaction survive in the system and the commit status information has + been discarded, this function will return NULL. Note that prepared + transactions are reported as in progress; applications must + check pg_prepared_xacts if they + need to determine whether the xid is a prepared transaction. + + + The functions shown in provide information about transactions that have been already committed. These functions mainly provide information about when the transactions diff --git a/src/backend/utils/adt/txid.c b/src/backend/utils/adt/txid.c index 772d7c7..8f86916 100644 --- a/src/backend/utils/adt/txid.c +++ b/src/backend/utils/adt/txid.c @@ -21,6 +21,7 @@ #include "postgres.h" +#include "access/clog.h" #include "access/transam.h" #include "access/xact.h" #include "access/xlog.h" @@ -28,6 +29,7 @@ #include "miscadmin.h" #include "libpq/pqformat.h" #include "postmaster/postmaster.h" +#include "storage/lwlock.h" #include "utils/builtins.h" #include "utils/memutils.h" #include "utils/snapmgr.h" @@ -93,6 +95,63 @@ load_xid_epoch(TxidEpoch *state) } /* + * Helper to get a TransactionId from a 64-bit xid with wraparound detection. + * + * It is an ERROR if the xid is in the future. Otherwise, returns true if + * the transaction is still new enough that we can determine whether it + * committed and false otherwise. If *extracted_xid is not NULL, it is set + * to the low 32 bits of the transaction ID (i.e. the actual XID, without the + * epoch). + */ +static bool +TransactionIdInRecentPast(uint64 xid_with_epoch, TransactionId *extracted_xid) +{ + uint32 xid_epoch = (uint32) (xid_with_epoch >> 32); + TransactionId xid = (TransactionId) xid_with_epoch; + uint32 now_epoch; + TransactionId now_epoch_last_xid; + + GetNextXidAndEpoch(&now_epoch_last_xid, &now_epoch); + + if (extracted_xid != NULL) + *extracted_xid = xid; + + /* For non-normal transaction IDs, we can ignore the epoch. */ + if (!TransactionIdIsNormal(xid)) + return true; + + /* If the transaction ID is in the future, throw an error. */ + if (xid_epoch > now_epoch + || (xid_epoch == now_epoch && xid > now_epoch_last_xid)) + ereport(ERROR, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("transaction ID " UINT64_FORMAT " is in the future", + xid_with_epoch))); + + /* + * ShmemVariableCache->oldestXid is protected by XidGenLock, but we don't + * acquire that lock here. Instead, we require the caller to acquire it, + * because the caller is presumably going to look up the returned XID. + * If we took and released the lock within this function, a CLOG + * truncation could occur before the caller finished with the XID. + */ + Assert(LWLockHeldByMe(XidGenLock)); + + /* + * If the transaction ID has wrapped around, it's definitely too old to + * determine the commit status. Otherwise, we can compare it to + * ShmemVariableCache->oldestXid to determine whether the relevant CLOG + * entry is guaranteed to still exist. + */ + if (xid_epoch + 1 < now_epoch + || (xid_epoch + 1 == now_epoch && xid < now_epoch_last_xid) + || TransactionIdPrecedes(xid, ShmemVariableCache->oldestXid)) + return false; + + return true; +} + +/* * do a TransactionId -> txid conversion for an XID near the given epoch */ static txid @@ -354,6 +413,9 @@ bad_format: * * Return the current toplevel transaction ID as TXID * If the current transaction does not have one, one is assigned. + * + * This value has the epoch as the high 32 bits and the 32-bit xid + * as the low 32 bits. */ Datum txid_current(PG_FUNCTION_ARGS) @@ -658,3 +720,57 @@ txid_snapshot_xip(PG_FUNCTION_ARGS) SRF_RETURN_DONE(fctx); } } + +/* + * Report the status of a recent transaction ID, or null for wrapped, + * truncated away or otherwise too old XIDs. + */ +Datum +txid_status(PG_FUNCTION_ARGS) +{ + const char *status; + uint64 xid_with_epoch = PG_GETARG_INT64(0); + TransactionId xid; + + /* + * Ensure clog isn't removed between when we check whether the current xid + * is valid and when we look its status up. + */ + LWLockAcquire(XidGenLock, LW_SHARED); + if (TransactionIdInRecentPast(xid_with_epoch, &xid)) + { + if (!TransactionIdIsValid(xid)) + { + LWLockRelease(XidGenLock); + ereport(ERROR, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("transaction ID " UINT64_FORMAT " is an invalid xid", + xid_with_epoch))); + } + + if (TransactionIdIsCurrentTransactionId(xid)) + status = gettext_noop("in progress"); + else if (TransactionIdDidCommit(xid)) + status = gettext_noop("committed"); + else if (TransactionIdDidAbort(xid)) + status = gettext_noop("aborted"); + else + + /* + * can't test TransactionIdIsInProgress here or we race with + * concurrent commit/abort. There's no point anyway, since it + * might then commit/abort just after we check. + */ + status = gettext_noop("in progress"); + } + else + { + status = NULL; + } + LWLockRelease(XidGenLock); + + if (status == NULL) + PG_RETURN_NULL(); + else + PG_RETURN_TEXT_P(cstring_to_text(status)); +} diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h index ab12761..912cb5a 100644 --- a/src/include/catalog/pg_proc.h +++ b/src/include/catalog/pg_proc.h @@ -4936,6 +4936,8 @@ DATA(insert OID = 2947 ( txid_snapshot_xip PGNSP PGUID 12 1 50 0 0 f f f f t DESCR("get set of in-progress txids in snapshot"); DATA(insert OID = 2948 ( txid_visible_in_snapshot PGNSP PGUID 12 1 0 0 0 f f f f t f i s 2 0 16 "20 2970" _null_ _null_ _null_ _null_ _null_ txid_visible_in_snapshot _null_ _null_ _null_ )); DESCR("is txid visible in snapshot?"); +DATA(insert OID = 3360 ( txid_status PGNSP PGUID 12 1 0 0 0 f f f f t f v s 1 0 25 "20" _null_ _null_ _null_ _null_ _null_ txid_status _null_ _null_ _null_ )); +DESCR("commit status of transaction"); /* record comparison using normal comparison rules */ DATA(insert OID = 2981 ( record_eq PGNSP PGUID 12 1 0 0 0 f f f f t f i s 2 0 16 "2249 2249" _null_ _null_ _null_ _null_ _null_ record_eq _null_ _null_ _null_ )); diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h index 5bdca82..26f76ca 100644 --- a/src/include/utils/builtins.h +++ b/src/include/utils/builtins.h @@ -119,5 +119,169 @@ extern int32 type_maximum_size(Oid type_oid, int32 typemod); /* quote.c */ extern char *quote_literal_cstr(const char *rawstr); +extern Datum quote_nullable(PG_FUNCTION_ARGS); + +/* guc.c */ +extern Datum show_config_by_name(PG_FUNCTION_ARGS); +extern Datum show_config_by_name_missing_ok(PG_FUNCTION_ARGS); +extern Datum set_config_by_name(PG_FUNCTION_ARGS); +extern Datum show_all_settings(PG_FUNCTION_ARGS); +extern Datum show_all_file_settings(PG_FUNCTION_ARGS); + +/* pg_config.c */ +extern Datum pg_config(PG_FUNCTION_ARGS); + +/* pg_controldata.c */ +extern Datum pg_control_checkpoint(PG_FUNCTION_ARGS); +extern Datum pg_control_system(PG_FUNCTION_ARGS); +extern Datum pg_control_init(PG_FUNCTION_ARGS); +extern Datum pg_control_recovery(PG_FUNCTION_ARGS); + +/* rls.c */ +extern Datum row_security_active(PG_FUNCTION_ARGS); +extern Datum row_security_active_name(PG_FUNCTION_ARGS); + +/* lockfuncs.c */ +extern Datum pg_lock_status(PG_FUNCTION_ARGS); +extern Datum pg_blocking_pids(PG_FUNCTION_ARGS); +extern Datum pg_advisory_lock_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_xact_lock_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_lock_shared_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_lock_int8(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_xact_lock_int8(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_lock_shared_int8(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_unlock_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_unlock_shared_int8(PG_FUNCTION_ARGS); +extern Datum pg_advisory_lock_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_xact_lock_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_lock_shared_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_lock_int4(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_xact_lock_int4(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_lock_shared_int4(PG_FUNCTION_ARGS); +extern Datum pg_try_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_unlock_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_unlock_shared_int4(PG_FUNCTION_ARGS); +extern Datum pg_advisory_unlock_all(PG_FUNCTION_ARGS); + +/* txid.c */ +extern Datum txid_snapshot_in(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_out(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_recv(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_send(PG_FUNCTION_ARGS); +extern Datum txid_current(PG_FUNCTION_ARGS); +extern Datum txid_current_if_assigned(PG_FUNCTION_ARGS); +extern Datum txid_current_snapshot(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_xmin(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_xmax(PG_FUNCTION_ARGS); +extern Datum txid_snapshot_xip(PG_FUNCTION_ARGS); +extern Datum txid_visible_in_snapshot(PG_FUNCTION_ARGS); +extern Datum txid_status(PG_FUNCTION_ARGS); + +/* uuid.c */ +extern Datum uuid_in(PG_FUNCTION_ARGS); +extern Datum uuid_out(PG_FUNCTION_ARGS); +extern Datum uuid_send(PG_FUNCTION_ARGS); +extern Datum uuid_recv(PG_FUNCTION_ARGS); +extern Datum uuid_lt(PG_FUNCTION_ARGS); +extern Datum uuid_le(PG_FUNCTION_ARGS); +extern Datum uuid_eq(PG_FUNCTION_ARGS); +extern Datum uuid_ge(PG_FUNCTION_ARGS); +extern Datum uuid_gt(PG_FUNCTION_ARGS); +extern Datum uuid_ne(PG_FUNCTION_ARGS); +extern Datum uuid_cmp(PG_FUNCTION_ARGS); +extern Datum uuid_sortsupport(PG_FUNCTION_ARGS); +extern Datum uuid_hash(PG_FUNCTION_ARGS); + +/* windowfuncs.c */ +extern Datum window_row_number(PG_FUNCTION_ARGS); +extern Datum window_rank(PG_FUNCTION_ARGS); +extern Datum window_dense_rank(PG_FUNCTION_ARGS); +extern Datum window_percent_rank(PG_FUNCTION_ARGS); +extern Datum window_cume_dist(PG_FUNCTION_ARGS); +extern Datum window_ntile(PG_FUNCTION_ARGS); +extern Datum window_lag(PG_FUNCTION_ARGS); +extern Datum window_lag_with_offset(PG_FUNCTION_ARGS); +extern Datum window_lag_with_offset_and_default(PG_FUNCTION_ARGS); +extern Datum window_lead(PG_FUNCTION_ARGS); +extern Datum window_lead_with_offset(PG_FUNCTION_ARGS); +extern Datum window_lead_with_offset_and_default(PG_FUNCTION_ARGS); +extern Datum window_first_value(PG_FUNCTION_ARGS); +extern Datum window_last_value(PG_FUNCTION_ARGS); +extern Datum window_nth_value(PG_FUNCTION_ARGS); + +/* access/spgist/spgquadtreeproc.c */ +extern Datum spg_quad_config(PG_FUNCTION_ARGS); +extern Datum spg_quad_choose(PG_FUNCTION_ARGS); +extern Datum spg_quad_picksplit(PG_FUNCTION_ARGS); +extern Datum spg_quad_inner_consistent(PG_FUNCTION_ARGS); +extern Datum spg_quad_leaf_consistent(PG_FUNCTION_ARGS); + +/* access/spgist/spgkdtreeproc.c */ +extern Datum spg_kd_config(PG_FUNCTION_ARGS); +extern Datum spg_kd_choose(PG_FUNCTION_ARGS); +extern Datum spg_kd_picksplit(PG_FUNCTION_ARGS); +extern Datum spg_kd_inner_consistent(PG_FUNCTION_ARGS); + +/* access/spgist/spgtextproc.c */ +extern Datum spg_text_config(PG_FUNCTION_ARGS); +extern Datum spg_text_choose(PG_FUNCTION_ARGS); +extern Datum spg_text_picksplit(PG_FUNCTION_ARGS); +extern Datum spg_text_inner_consistent(PG_FUNCTION_ARGS); +extern Datum spg_text_leaf_consistent(PG_FUNCTION_ARGS); + +/* access/gin/ginarrayproc.c */ +extern Datum ginarrayextract(PG_FUNCTION_ARGS); +extern Datum ginarrayextract_2args(PG_FUNCTION_ARGS); +extern Datum ginqueryarrayextract(PG_FUNCTION_ARGS); +extern Datum ginarrayconsistent(PG_FUNCTION_ARGS); +extern Datum ginarraytriconsistent(PG_FUNCTION_ARGS); + +/* access/tablesample/bernoulli.c */ +extern Datum tsm_bernoulli_handler(PG_FUNCTION_ARGS); + +/* access/tablesample/system.c */ +extern Datum tsm_system_handler(PG_FUNCTION_ARGS); + +/* access/transam/twophase.c */ +extern Datum pg_prepared_xact(PG_FUNCTION_ARGS); + +/* access/transam/multixact.c */ +extern Datum pg_get_multixact_members(PG_FUNCTION_ARGS); + +/* access/transam/committs.c */ +extern Datum pg_xact_commit_timestamp(PG_FUNCTION_ARGS); +extern Datum pg_last_committed_xact(PG_FUNCTION_ARGS); + +/* catalogs/dependency.c */ +extern Datum pg_describe_object(PG_FUNCTION_ARGS); +extern Datum pg_identify_object(PG_FUNCTION_ARGS); +extern Datum pg_identify_object_as_address(PG_FUNCTION_ARGS); + +/* catalog/objectaddress.c */ +extern Datum pg_get_object_address(PG_FUNCTION_ARGS); + +/* commands/constraint.c */ +extern Datum unique_key_recheck(PG_FUNCTION_ARGS); + +/* commands/event_trigger.c */ +extern Datum pg_event_trigger_dropped_objects(PG_FUNCTION_ARGS); +extern Datum pg_event_trigger_table_rewrite_oid(PG_FUNCTION_ARGS); +extern Datum pg_event_trigger_table_rewrite_reason(PG_FUNCTION_ARGS); +extern Datum pg_event_trigger_ddl_commands(PG_FUNCTION_ARGS); + +/* commands/extension.c */ +extern Datum pg_available_extensions(PG_FUNCTION_ARGS); +extern Datum pg_available_extension_versions(PG_FUNCTION_ARGS); +extern Datum pg_extension_update_paths(PG_FUNCTION_ARGS); +extern Datum pg_extension_config_dump(PG_FUNCTION_ARGS); + +/* commands/prepare.c */ +extern Datum pg_prepared_statement(PG_FUNCTION_ARGS); + +/* utils/mmgr/portalmem.c */ +extern Datum pg_cursor(PG_FUNCTION_ARGS); #endif /* BUILTINS_H */ diff --git a/src/test/regress/expected/txid.out b/src/test/regress/expected/txid.out index 802ccb9..015dae3 100644 --- a/src/test/regress/expected/txid.out +++ b/src/test/regress/expected/txid.out @@ -254,3 +254,71 @@ SELECT txid_current_if_assigned() IS NOT DISTINCT FROM BIGINT :'txid_current'; (1 row) COMMIT; +-- test xid status functions +BEGIN; +SELECT txid_current() AS committed \gset +COMMIT; +BEGIN; +SELECT txid_current() AS rolledback \gset +ROLLBACK; +BEGIN; +SELECT txid_current() AS inprogress \gset +SELECT txid_status(:committed) AS committed; + committed +----------- + committed +(1 row) + +SELECT txid_status(:rolledback) AS rolledback; + rolledback +------------ + aborted +(1 row) + +SELECT txid_status(:inprogress) AS inprogress; + inprogress +------------- + in progress +(1 row) + +SELECT txid_status(1); -- BootstrapTransactionId is always committed + txid_status +------------- + committed +(1 row) + +SELECT txid_status(2); -- FrozenTransactionId is always committed + txid_status +------------- + committed +(1 row) + +SELECT txid_status(3); -- in regress testing FirstNormalTransactionId will always be behind oldestXmin + txid_status +------------- + +(1 row) + +COMMIT; +BEGIN; +CREATE FUNCTION test_future_xid_status(bigint) +RETURNS void +LANGUAGE plpgsql +AS +$$ +BEGIN + PERFORM txid_status($1); + RAISE EXCEPTION 'didn''t ERROR at xid in the future as expected'; +EXCEPTION + WHEN invalid_parameter_value THEN + RAISE NOTICE 'Got expected error for xid in the future'; +END; +$$; +SELECT test_future_xid_status(:inprogress + 10000); +NOTICE: Got expected error for xid in the future + test_future_xid_status +------------------------ + +(1 row) + +ROLLBACK; diff --git a/src/test/regress/sql/txid.sql b/src/test/regress/sql/txid.sql index 4aefd9e..bd6decf 100644 --- a/src/test/regress/sql/txid.sql +++ b/src/test/regress/sql/txid.sql @@ -59,3 +59,41 @@ SELECT txid_current_if_assigned() IS NULL; SELECT txid_current() \gset SELECT txid_current_if_assigned() IS NOT DISTINCT FROM BIGINT :'txid_current'; COMMIT; + +-- test xid status functions +BEGIN; +SELECT txid_current() AS committed \gset +COMMIT; + +BEGIN; +SELECT txid_current() AS rolledback \gset +ROLLBACK; + +BEGIN; +SELECT txid_current() AS inprogress \gset + +SELECT txid_status(:committed) AS committed; +SELECT txid_status(:rolledback) AS rolledback; +SELECT txid_status(:inprogress) AS inprogress; +SELECT txid_status(1); -- BootstrapTransactionId is always committed +SELECT txid_status(2); -- FrozenTransactionId is always committed +SELECT txid_status(3); -- in regress testing FirstNormalTransactionId will always be behind oldestXmin + +COMMIT; + +BEGIN; +CREATE FUNCTION test_future_xid_status(bigint) +RETURNS void +LANGUAGE plpgsql +AS +$$ +BEGIN + PERFORM txid_status($1); + RAISE EXCEPTION 'didn''t ERROR at xid in the future as expected'; +EXCEPTION + WHEN invalid_parameter_value THEN + RAISE NOTICE 'Got expected error for xid in the future'; +END; +$$; +SELECT test_future_xid_status(:inprogress + 10000); +ROLLBACK; -- 2.5.5