Use snapshot to check tuple visibility in pre-update state (#28)
When multiple tables are updated or the view contains a self-join, we need to calculate table states that was before it is modified during incremental view maintenance. For get the pre-update state, tuples inserted in a command must be removed when the table is scanned. Previously, we used xmin and cmin system columns for this purpose, but this way is problematic because after a tuple is frozen, its xmin no longer has any meaning. Actually, we will get inconsistent view results after XID wraparound. Also, we can see similar similar inconsistency when using sub-transaction because xmin values do not always monotonically increasing by command executions. To fix this, we use a snapshot that taken just before the table is modified for checking tuple visibility in pre-state table instead of using xmin and cmin system columns. A new function returning boolean, ivm_visible_in_prestate, is added, and this is called in WHERE clause of sub-queries to calculate pre-state table. This function check if a specified tuple in the post-update table is visible or not using the snapshot and return true if the tuple is visible.
This commit is contained in:
Yugo Nagata
GitHub
parent
5f584e54c3
commit
b6702f9a3a
5 changed files with 124 additions and 26 deletions
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@ -518,6 +518,24 @@ SELECT * FROM mv_self ORDER BY v1;
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300 | 300
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(4 rows)
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--- with sub-transactions
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SAVEPOINT p1;
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INSERT INTO base_t VALUES (7,70);
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RELEASE SAVEPOINT p1;
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INSERT INTO base_t VALUES (7,77);
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SELECT * FROM mv_self ORDER BY v1, v2;
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v1 | v2
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-----+-----
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50 | 50
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60 | 60
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70 | 70
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70 | 77
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77 | 70
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77 | 77
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130 | 130
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300 | 300
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(8 rows)
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ROLLBACK;
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-- support simultaneous table changes
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BEGIN;
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116
matview.c
116
matview.c
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@ -14,6 +14,7 @@
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#include "access/genam.h"
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#include "access/multixact.h"
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#include "access/table.h"
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#include "access/tableam.h"
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#include "access/xact.h"
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#include "catalog/pg_depend.h"
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#include "catalog/heap.h"
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@ -90,8 +91,7 @@ typedef struct MV_TriggerHashEntry
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int before_trig_count; /* count of before triggers invoked */
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int after_trig_count; /* count of after triggers invoked */
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TransactionId xid; /* Transaction id before the first table is modified*/
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CommandId cid; /* Command id before the first table is modified */
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Snapshot snapshot; /* Snapshot just before table change */
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List *tables; /* List of MV_TriggerTable */
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bool has_old; /* tuples are deleted from any table? */
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@ -113,11 +113,16 @@ typedef struct MV_TriggerTable
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List *rte_paths; /* List of paths to RTE index of the modified table */
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RangeTblEntry *original_rte; /* the original RTE saved before rewriting query */
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Relation rel; /* relation of the modified table */
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TupleTableSlot *slot; /* for checking visibility in the pre-state table */
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} MV_TriggerTable;
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static HTAB *mv_query_cache = NULL;
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static HTAB *mv_trigger_info = NULL;
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static bool in_delta_calculation = false;
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/* kind of IVM operation for the view */
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typedef enum
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{
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@ -141,13 +146,11 @@ static void OpenImmvIncrementalMaintenance(void);
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static void CloseImmvIncrementalMaintenance(void);
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static Query *rewrite_query_for_preupdate_state(Query *query, List *tables,
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TransactionId xid, CommandId cid,
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ParseState *pstate, List *rte_path);
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ParseState *pstate, List *rte_path, Oid matviewid);
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static void register_delta_ENRs(ParseState *pstate, Query *query, List *tables);
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static char *make_delta_enr_name(const char *prefix, Oid relid, int count);
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static RangeTblEntry *get_prestate_rte(RangeTblEntry *rte, MV_TriggerTable *table,
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TransactionId xid, CommandId cid,
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QueryEnvironment *queryEnv);
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QueryEnvironment *queryEnv, Oid matviewid);
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static RangeTblEntry *union_ENRs(RangeTblEntry *rte, Oid relid, List *enr_rtes, const char *prefix,
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QueryEnvironment *queryEnv);
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static Query *rewrite_query_for_distinct_and_aggregates(Query *query, ParseState *pstate);
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@ -203,13 +206,14 @@ static void mv_InitHashTables(void);
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static SPIPlanPtr mv_FetchPreparedPlan(MV_QueryKey *key);
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static void mv_HashPreparedPlan(MV_QueryKey *key, SPIPlanPtr plan);
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static void mv_BuildQueryKey(MV_QueryKey *key, Oid matview_id, int32 query_type);
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static void clean_up_IVM_hash_entry(MV_TriggerHashEntry *entry);
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static void clean_up_IVM_hash_entry(MV_TriggerHashEntry *entry, bool is_abort);
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static List *get_securityQuals(Oid relId, int rt_index, Query *query);
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/* SQL callable functions */
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PG_FUNCTION_INFO_V1(IVM_immediate_before);
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PG_FUNCTION_INFO_V1(IVM_immediate_maintenance);
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PG_FUNCTION_INFO_V1(ivm_visible_in_prestate);
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/*
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* ExecRefreshImmv -- execute a refresh_immv() function
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@ -710,13 +714,16 @@ IVM_immediate_before(PG_FUNCTION_ARGS)
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/* On the first BEFORE to update the view, initialize trigger data */
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if (!found)
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{
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/*
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* Get a snapshot just before the table was modified for checking
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* tuple visibility in the pre-update state of the table.
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*/
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Snapshot snapshot = GetActiveSnapshot();
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entry->matview_id = matviewOid;
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entry->before_trig_count = 0;
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entry->after_trig_count = 0;
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entry->xid = GetCurrentTransactionId();
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entry->cid = snapshot->curcid;
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entry->snapshot = RegisterSnapshot(snapshot);
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entry->tables = NIL;
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entry->has_old = false;
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entry->has_new = false;
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@ -811,6 +818,8 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
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table->old_rtes = NIL;
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table->new_rtes = NIL;
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table->rte_paths = NIL;
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table->slot = MakeSingleTupleTableSlot(RelationGetDescr(rel), table_slot_callbacks(rel));
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table->rel = table_open(RelationGetRelid(rel), NoLock);
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entry->tables = lappend(entry->tables, table);
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MemoryContextSwitchTo(oldcxt);
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@ -933,7 +942,7 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
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}
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/* Clean up hash entry and delete tuplestores */
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clean_up_IVM_hash_entry(entry);
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clean_up_IVM_hash_entry(entry, false);
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/* Pop the original snapshot. */
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PopActiveSnapshot();
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@ -969,8 +978,7 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
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/* Set all tables in the query to pre-update state */
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rewritten = rewrite_query_for_preupdate_state(rewritten, entry->tables,
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entry->xid, entry->cid,
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pstate, NIL);
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pstate, NIL, matviewOid);
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/* Rewrite for DISTINCT clause and aggregates functions */
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rewritten = rewrite_query_for_distinct_and_aggregates(rewritten, pstate);
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@ -1069,7 +1077,7 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
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}
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/* Clean up hash entry and delete tuplestores */
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clean_up_IVM_hash_entry(entry);
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clean_up_IVM_hash_entry(entry, false);
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if (old_tuplestore)
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{
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dest_old->rDestroy(dest_old);
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@ -1100,13 +1108,11 @@ IVM_immediate_maintenance(PG_FUNCTION_ARGS)
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*
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* Rewrite the query so that base tables' RTEs will represent "pre-update"
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* state of tables. This is necessary to calculate view delta after multiple
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* tables are modified. xid and cid are the transaction id and command id
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* before the first table was modified.
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* tables are modified.
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*/
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static Query*
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rewrite_query_for_preupdate_state(Query *query, List *tables,
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TransactionId xid, CommandId cid,
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ParseState *pstate, List *rte_path)
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ParseState *pstate, List *rte_path, Oid matviewid)
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{
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ListCell *lc;
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int num_rte = list_length(query->rtable);
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@ -1129,7 +1135,7 @@ rewrite_query_for_preupdate_state(Query *query, List *tables,
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/* if rte contains subquery, search recursively */
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if (r->rtekind == RTE_SUBQUERY)
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rewrite_query_for_preupdate_state(r->subquery, tables, xid, cid, pstate, lappend_int(list_copy(rte_path), i));
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rewrite_query_for_preupdate_state(r->subquery, tables, pstate, lappend_int(list_copy(rte_path), i), matviewid);
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else
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{
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ListCell *lc2;
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@ -1142,7 +1148,7 @@ rewrite_query_for_preupdate_state(Query *query, List *tables,
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*/
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if (r->relid == table->table_id)
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{
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lfirst(lc) = get_prestate_rte(r, table, xid, cid, pstate->p_queryEnv);
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lfirst(lc) = get_prestate_rte(r, table, pstate->p_queryEnv, matviewid);
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table->rte_paths = lappend(table->rte_paths, lappend_int(list_copy(rte_path), i));
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break;
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}
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@ -1233,6 +1239,51 @@ register_delta_ENRs(ParseState *pstate, Query *query, List *tables)
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}
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}
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#define DatumGetItemPointer(X) ((ItemPointer) DatumGetPointer(X))
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#define PG_GETARG_ITEMPOINTER(n) DatumGetItemPointer(PG_GETARG_DATUM(n))
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/*
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* ivm_visible_in_prestate
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*
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* Check visibility of a tuple specified by the tableoid and item pointer
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* using the snapshot taken just before the table was modified.
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*/
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Datum
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ivm_visible_in_prestate(PG_FUNCTION_ARGS)
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{
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Oid tableoid = PG_GETARG_OID(0);
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ItemPointer itemPtr = PG_GETARG_ITEMPOINTER(1);
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Oid matviewOid = PG_GETARG_OID(2);
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MV_TriggerHashEntry *entry;
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MV_TriggerTable *table = NULL;
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ListCell *lc;
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bool found;
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bool result;
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if (!in_delta_calculation)
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ereport(ERROR,
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(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
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errmsg("ivm_visible_in_prestate can be called only in delta calculation")));
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entry = (MV_TriggerHashEntry *) hash_search(mv_trigger_info,
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(void *) &matviewOid,
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HASH_FIND, &found);
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Assert (found && entry != NULL);
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foreach(lc, entry->tables)
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{
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table = (MV_TriggerTable *) lfirst(lc);
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if (table->table_id == tableoid)
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break;
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}
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Assert (table != NULL);
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result = table_tuple_fetch_row_version(table->rel, itemPtr, entry->snapshot, table->slot);
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PG_RETURN_BOOL(result);
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}
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/*
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* get_prestate_rte
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*
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@ -1241,8 +1292,7 @@ register_delta_ENRs(ParseState *pstate, Query *query, List *tables)
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*/
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static RangeTblEntry*
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get_prestate_rte(RangeTblEntry *rte, MV_TriggerTable *table,
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TransactionId xid, CommandId cid,
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QueryEnvironment *queryEnv)
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QueryEnvironment *queryEnv, Oid matviewid)
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{
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StringInfoData str;
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RawStmt *raw;
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@ -1269,9 +1319,8 @@ get_prestate_rte(RangeTblEntry *rte, MV_TriggerTable *table,
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initStringInfo(&str);
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appendStringInfo(&str,
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"SELECT t.* FROM %s t"
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" WHERE (age(t.xmin) - age(%u::text::xid) > 0) OR"
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" (t.xmin = %u AND t.cmin::text::int < %u)",
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relname, xid, xid, cid);
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" WHERE ivm_visible_in_prestate(t.tableoid, t.ctid ,%d::oid)",
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relname, matviewid);
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for (i = 0; i < list_length(table->old_tuplestores); i++)
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{
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@ -1481,6 +1530,8 @@ calc_delta(MV_TriggerTable *table, List *rte_path, Query *query,
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ListCell *lc = getRteListCell(query, rte_path);
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RangeTblEntry *rte = (RangeTblEntry *) lfirst(lc);
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in_delta_calculation = true;
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/* Generate old delta */
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if (list_length(table->old_rtes) > 0)
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{
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@ -1496,6 +1547,8 @@ calc_delta(MV_TriggerTable *table, List *rte_path, Query *query,
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lfirst(lc) = union_ENRs(rte, table->table_id, table->new_rtes, "new", queryEnv);
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refresh_immv_datafill(dest_new, query, queryEnv, tupdesc_new, "");
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}
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in_delta_calculation = false;
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}
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/*
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@ -2833,8 +2886,10 @@ AtAbort_IVM()
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{
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hash_seq_init(&seq, mv_trigger_info);
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while ((entry = hash_seq_search(&seq)) != NULL)
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clean_up_IVM_hash_entry(entry);
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clean_up_IVM_hash_entry(entry, true);
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}
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in_delta_calculation = false;
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}
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/*
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@ -2844,7 +2899,7 @@ AtAbort_IVM()
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* maintenance finished.
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*/
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static void
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clean_up_IVM_hash_entry(MV_TriggerHashEntry *entry)
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clean_up_IVM_hash_entry(MV_TriggerHashEntry *entry, bool is_abort)
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{
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bool found;
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ListCell *lc;
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@ -2867,9 +2922,18 @@ clean_up_IVM_hash_entry(MV_TriggerHashEntry *entry)
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list_free(table->old_tuplestores);
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list_free(table->new_tuplestores);
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if (!is_abort)
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{
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ExecDropSingleTupleTableSlot(table->slot);
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table_close(table->rel, NoLock);
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}
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}
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list_free(entry->tables);
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if (!is_abort)
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UnregisterSnapshot(entry->snapshot);
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hash_search(mv_trigger_info, (void *) &entry->matview_id, HASH_REMOVE, &found);
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}
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@ -0,0 +1,7 @@
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-- functions
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CREATE FUNCTION ivm_visible_in_prestate(oid, tid, oid)
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RETURNS bool
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STABLE
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AS 'MODULE_PATHNAME', 'ivm_visible_in_prestate'
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LANGUAGE C;
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1
pg_ivm.h
1
pg_ivm.h
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@ -49,6 +49,7 @@ extern bool ImmvIncrementalMaintenanceIsEnabled(void);
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extern Query *get_immv_query(Relation matviewRel);
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extern Datum IVM_immediate_before(PG_FUNCTION_ARGS);
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extern Datum IVM_immediate_maintenance(PG_FUNCTION_ARGS);
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extern Datum ivm_visible_in_prestate(PG_FUNCTION_ARGS);
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extern void AtAbort_IVM(void);
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extern bool isIvmName(const char *s);
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@ -168,6 +168,14 @@ WITH
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dlt_t AS (DELETE FROM base_t WHERE i IN (4,5) RETURNING 1)
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SELECT NULL;
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SELECT * FROM mv_self ORDER BY v1;
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--- with sub-transactions
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SAVEPOINT p1;
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INSERT INTO base_t VALUES (7,70);
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RELEASE SAVEPOINT p1;
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INSERT INTO base_t VALUES (7,77);
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SELECT * FROM mv_self ORDER BY v1, v2;
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ROLLBACK;
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-- support simultaneous table changes
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