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pg_shard.c
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pg_shard.c
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/*-------------------------------------------------------------------------
*
* pg_shard.c
*
* This file contains functions to perform distributed planning and execution of
* distributed tables.
*
* Copyright (c) 2014, Citus Data, Inc.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "c.h"
#include "fmgr.h"
#include "funcapi.h"
#include "libpq-fe.h"
#include "miscadmin.h"
#include "postgres_ext.h"
#include "pg_shard.h"
#include "connection.h"
#include "create_shards.h"
#include "distribution_metadata.h"
#include "prune_shard_list.h"
#include "ruleutils.h"
#include <stddef.h>
#include <string.h>
#include "access/heapam.h"
#include "access/htup_details.h"
#include "access/htup.h"
#include "access/sdir.h"
#include "access/skey.h"
#include "access/tupdesc.h"
#include "access/xact.h"
#include "catalog/namespace.h"
#include "catalog/pg_class.h"
#include "catalog/pg_type.h"
#include "commands/extension.h"
#include "executor/execdesc.h"
#include "executor/executor.h"
#include "executor/instrument.h"
#include "executor/tuptable.h"
#include "nodes/execnodes.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "nodes/nodes.h"
#include "nodes/params.h"
#include "nodes/parsenodes.h"
#include "nodes/pg_list.h"
#include "nodes/plannodes.h"
#include "nodes/primnodes.h"
#include "optimizer/clauses.h"
#include "optimizer/cost.h"
#include "optimizer/planner.h"
#include "optimizer/var.h"
#include "parser/analyze.h"
#include "parser/parse_node.h"
#include "parser/parsetree.h"
#include "parser/parse_type.h"
#include "storage/lock.h"
#include "tcop/dest.h"
#include "tcop/tcopprot.h"
#include "tcop/utility.h"
#include "utils/builtins.h"
#include "utils/elog.h"
#include "utils/errcodes.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/palloc.h"
#include "utils/rel.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
#include "utils/tuplestore.h"
/* controls use of locks to enforce safe commutativity */
bool AllModificationsCommutative = false;
/* informs pg_shard to use the CitusDB planner */
bool UseCitusDBSelectLogic = false;
/* planner functions forward declarations */
static PlannedStmt * PgShardPlanner(Query *parse, int cursorOptions,
ParamListInfo boundParams);
static PlannerType DeterminePlannerType(Query *query);
static void ErrorIfQueryNotSupported(Query *queryTree);
static Oid ExtractFirstDistributedTableId(Query *query);
static bool ExtractRangeTableEntryWalker(Node *node, List **rangeTableList);
static List * DistributedQueryShardList(Query *query);
static bool SelectFromMultipleShards(Query *query, List *queryShardList);
static PlannedStmt * PlanSequentialScan(Query *query, int cursorOptions,
ParamListInfo boundParams);
static Query * RowAndColumnFilterQuery(Query *query);
static List * QueryRestrictList(Query *query);
static Const * ExtractPartitionValue(Query *query, Var *partitionColumn);
static bool ExtractFromExpressionWalker(Node *node, List **qualifierList);
static List * QueryFromList(List *rangeTableList);
static List * TargetEntryList(List *expressionList);
static CreateStmt * CreateTemporaryTableLikeStmt(Oid sourceRelationId);
static DistributedPlan * BuildDistributedPlan(Query *query, List *shardIntervalList);
/* executor functions forward declarations */
static void PgShardExecutorStart(QueryDesc *queryDesc, int eflags);
static bool IsPgShardPlan(PlannedStmt *plannedStmt);
static LOCKMODE CommutativityRuleToLockMode(CmdType commandType);
static void AcquireExecutorShardLocks(List *taskList, LOCKMODE lockMode);
static int CompareTasksByShardId(const void *leftElement, const void *rightElement);
static void ExecuteMultipleShardSelect(DistributedPlan *distributedPlan,
RangeVar *intermediateTable);
static bool ExecuteTaskAndStoreResults(Task *task, TupleDesc tupleDescriptor,
Tuplestorestate *tupleStore);
static bool SendQueryInSingleRowMode(PGconn *connection, StringInfo query);
static bool StoreQueryResult(PGconn *connection, TupleDesc tupleDescriptor,
Tuplestorestate *tupleStore);
static void TupleStoreToTable(RangeVar *tableRangeVar, List *remoteTargetList,
TupleDesc storeTupleDescriptor, Tuplestorestate *store);
static void PgShardExecutorRun(QueryDesc *queryDesc, ScanDirection direction, long count);
static int32 ExecuteDistributedModify(DistributedPlan *distributedPlan);
static void ExecuteSingleShardSelect(DistributedPlan *distributedPlan,
EState *executorState, TupleDesc tupleDescriptor,
DestReceiver *destination);
static void PgShardExecutorFinish(QueryDesc *queryDesc);
static void PgShardExecutorEnd(QueryDesc *queryDesc);
static void PgShardProcessUtility(Node *parsetree, const char *queryString,
ProcessUtilityContext context, ParamListInfo params,
DestReceiver *dest, char *completionTag);
/* declarations for dynamic loading */
PG_MODULE_MAGIC;
/* saved hook values in case of unload */
static planner_hook_type PreviousPlannerHook = NULL;
static ExecutorStart_hook_type PreviousExecutorStartHook = NULL;
static ExecutorRun_hook_type PreviousExecutorRunHook = NULL;
static ExecutorFinish_hook_type PreviousExecutorFinishHook = NULL;
static ExecutorEnd_hook_type PreviousExecutorEndHook = NULL;
static ProcessUtility_hook_type PreviousProcessUtilityHook = NULL;
/*
* _PG_init is called when the module is loaded. In this function we save the
* previous utility hook, and then install our hook to pre-intercept calls to
* the copy command.
*/
void
_PG_init(void)
{
PreviousPlannerHook = planner_hook;
planner_hook = PgShardPlanner;
PreviousExecutorStartHook = ExecutorStart_hook;
ExecutorStart_hook = PgShardExecutorStart;
PreviousExecutorRunHook = ExecutorRun_hook;
ExecutorRun_hook = PgShardExecutorRun;
PreviousExecutorFinishHook = ExecutorFinish_hook;
ExecutorFinish_hook = PgShardExecutorFinish;
PreviousExecutorEndHook = ExecutorEnd_hook;
ExecutorEnd_hook = PgShardExecutorEnd;
PreviousProcessUtilityHook = ProcessUtility_hook;
ProcessUtility_hook = PgShardProcessUtility;
DefineCustomBoolVariable("pg_shard.all_modifications_commutative",
"Bypasses commutativity checks when enabled", NULL,
&AllModificationsCommutative, false, PGC_USERSET, 0, NULL,
NULL, NULL);
DefineCustomBoolVariable("pg_shard.use_citusdb_select_logic",
"Informs pg_shard to use CitusDB's select logic", NULL,
&UseCitusDBSelectLogic, false, PGC_USERSET, 0, NULL,
NULL, NULL);
EmitWarningsOnPlaceholders("pg_shard");
}
/*
* _PG_fini is called when the module is unloaded. This function uninstalls the
* extension's hooks.
*/
void
_PG_fini(void)
{
ProcessUtility_hook = PreviousProcessUtilityHook;
ExecutorRun_hook = PreviousExecutorRunHook;
ExecutorStart_hook = PreviousExecutorStartHook;
ExecutorFinish_hook = PreviousExecutorFinishHook;
ExecutorEnd_hook = PreviousExecutorEndHook;
planner_hook = PreviousPlannerHook;
}
/*
* PgShardPlanner implements custom planner logic to plan queries involving
* distributed tables. It first calls the standard planner to perform common
* mutations and normalizations on the query and retrieve the "normal" planned
* statement for the query. Further functions actually produce the distributed
* plan should one be necessary.
*/
static PlannedStmt *
PgShardPlanner(Query *query, int cursorOptions, ParamListInfo boundParams)
{
PlannedStmt *plannedStatement = NULL;
PlannerType plannerType = DeterminePlannerType(query);
if (plannerType == PLANNER_TYPE_PG_SHARD)
{
DistributedPlan *distributedPlan = NULL;
Query *distributedQuery = copyObject(query);
List *queryShardList = NIL;
bool selectFromMultipleShards = false;
CreateStmt *createTemporaryTableStmt = NULL;
/* call standard planner first to have Query transformations performed */
plannedStatement = standard_planner(distributedQuery, cursorOptions,
boundParams);
ErrorIfQueryNotSupported(distributedQuery);
/* compute the list of shards this query needs to access */
queryShardList = DistributedQueryShardList(distributedQuery);
/*
* If a select query touches multiple shards, we don't push down the
* query as-is, and instead only push down the filter clauses and select
* needed columns. We then copy those results to a local temporary table
* and then modify the original PostgreSQL plan to perform a sequential
* scan on that temporary table.
* XXX: This approach is limited as we cannot handle index or foreign
* scans. We will revisit this by potentially using another type of scan
* node instead of a sequential scan.
*/
selectFromMultipleShards = SelectFromMultipleShards(query, queryShardList);
if (selectFromMultipleShards)
{
Oid distributedTableId = InvalidOid;
/*
* Force a sequential scan as we change the underlying table to
* point to our intermediate temporary table which contains the
* fetched data.
*/
plannedStatement = PlanSequentialScan(query, cursorOptions, boundParams);
distributedQuery = RowAndColumnFilterQuery(distributedQuery);
/* construct a CreateStmt to clone the existing table */
distributedTableId = ExtractFirstDistributedTableId(distributedQuery);
createTemporaryTableStmt = CreateTemporaryTableLikeStmt(distributedTableId);
}
distributedPlan = BuildDistributedPlan(distributedQuery, queryShardList);
distributedPlan->originalPlan = plannedStatement->planTree;
distributedPlan->selectFromMultipleShards = selectFromMultipleShards;
distributedPlan->createTemporaryTableStmt = createTemporaryTableStmt;
plannedStatement->planTree = (Plan *) distributedPlan;
}
else if (plannerType == PLANNER_TYPE_CITUSDB)
{
Assert(PreviousPlannerHook != NULL);
plannedStatement = PreviousPlannerHook(query, cursorOptions, boundParams);
}
else if (plannerType == PLANNER_TYPE_POSTGRES)
{
if (PreviousPlannerHook != NULL)
{
plannedStatement = PreviousPlannerHook(query, cursorOptions, boundParams);
}
else
{
plannedStatement = standard_planner(query, cursorOptions, boundParams);
}
}
else
{
ereport(ERROR, (errmsg("unknown planner type: %d", plannerType)));
}
return plannedStatement;
}
/*
* DeterminePlannerType chooses the appropriate planner to use in order to plan
* the given query.
*/
static PlannerType
DeterminePlannerType(Query *query)
{
PlannerType plannerType = PLANNER_INVALID_FIRST;
CmdType commandType = query->commandType;
/* if the extension isn't created, we always use the postgres planner */
bool missingOK = true;
Oid extensionOid = get_extension_oid(PG_SHARD_EXTENSION_NAME, missingOK);
if (extensionOid == InvalidOid)
{
return PLANNER_TYPE_POSTGRES;
}
if (commandType == CMD_SELECT && UseCitusDBSelectLogic)
{
plannerType = PLANNER_TYPE_CITUSDB;
}
else if (commandType == CMD_SELECT || commandType == CMD_INSERT ||
commandType == CMD_UPDATE || commandType == CMD_DELETE)
{
Oid distributedTableId = ExtractFirstDistributedTableId(query);
if (OidIsValid(distributedTableId))
{
plannerType = PLANNER_TYPE_PG_SHARD;
}
else
{
plannerType = PLANNER_TYPE_POSTGRES;
}
}
else
{
/*
* For utility statements, we need to detect if they are operating on
* distributed tables. If they are, we need to warn or error out
* accordingly.
*/
plannerType = PLANNER_TYPE_POSTGRES;
}
return plannerType;
}
/*
* ErrorIfQueryNotSupported checks if the query contains unsupported features,
* and errors out if it does.
*/
static void
ErrorIfQueryNotSupported(Query *queryTree)
{
Oid distributedTableId = ExtractFirstDistributedTableId(queryTree);
Var *partitionColumn = PartitionColumn(distributedTableId);
List *rangeTableList = NIL;
ListCell *rangeTableCell = NULL;
bool hasValuesScan = false;
uint32 queryTableCount = 0;
bool hasNonConstTargetEntryExprs = false;
bool specifiesPartitionValue = false;
CmdType commandType = queryTree->commandType;
Assert(commandType == CMD_SELECT || commandType == CMD_INSERT ||
commandType == CMD_UPDATE || commandType == CMD_DELETE);
/* prevent utility statements like DECLARE CURSOR attached to selects */
if (commandType == CMD_SELECT && queryTree->utilityStmt != NULL)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("unsupported utility statement")));
}
/* extract range table entries */
ExtractRangeTableEntryWalker((Node *) queryTree, &rangeTableList);
foreach(rangeTableCell, rangeTableList)
{
RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell);
if (rangeTableEntry->rtekind == RTE_RELATION)
{
queryTableCount++;
}
else if (rangeTableEntry->rtekind == RTE_VALUES)
{
hasValuesScan = true;
}
else
{
/* reject subquery, join, function or CTE range table entries */
ereport(ERROR, (errmsg("unsupported range table type: %d",
rangeTableEntry->rtekind)));
}
}
/* reject queries which involve joins */
if (queryTableCount != 1)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot perform distributed planning on this query"),
errdetail("Joins are currently unsupported")));
}
/* reject queries which involve multi-row inserts */
if (hasValuesScan)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("multi-row INSERTs to distributed tables "
"are not supported")));
}
/* reject queries with a returning list */
if (list_length(queryTree->returningList) > 0)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot plan sharded modification that uses a "
"RETURNING clause")));
}
if (commandType == CMD_INSERT || commandType == CMD_UPDATE ||
commandType == CMD_DELETE)
{
ListCell *targetEntryCell = NULL;
foreach(targetEntryCell, queryTree->targetList)
{
TargetEntry *targetEntry = (TargetEntry *) lfirst(targetEntryCell);
/* skip resjunk entries: UPDATE adds some for ctid, etc. */
if (targetEntry->resjunk)
{
continue;
}
if (!IsA(targetEntry->expr, Const))
{
hasNonConstTargetEntryExprs = true;
}
if (targetEntry->resno == partitionColumn->varattno)
{
specifiesPartitionValue = true;
}
}
}
if (hasNonConstTargetEntryExprs)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot plan sharded modification containing values "
"which are not constants or constant expressions")));
}
if (specifiesPartitionValue && (commandType == CMD_UPDATE))
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("modifying the partition value of rows is not allowed")));
}
}
/*
* ExtractFirstDistributedTableId takes a given query, and finds the relationId
* for the first distributed table in that query. If the function cannot find a
* distributed table, it returns InvalidOid.
*/
static Oid
ExtractFirstDistributedTableId(Query *query)
{
List *rangeTableList = NIL;
ListCell *rangeTableCell = NULL;
Oid distributedTableId = InvalidOid;
/* extract range table entries */
ExtractRangeTableEntryWalker((Node *) query, &rangeTableList);
foreach(rangeTableCell, rangeTableList)
{
RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell);
if (IsDistributedTable(rangeTableEntry->relid))
{
distributedTableId = rangeTableEntry->relid;
break;
}
}
return distributedTableId;
}
/*
* ExtractRangeTableEntryWalker walks over a query tree, and finds all range
* table entries. For recursing into the query tree, this function uses the
* query tree walker since the expression tree walker doesn't recurse into
* sub-queries.
*/
static bool
ExtractRangeTableEntryWalker(Node *node, List **rangeTableList)
{
bool walkIsComplete = false;
if (node == NULL)
{
return false;
}
if (IsA(node, RangeTblEntry))
{
RangeTblEntry *rangeTable = (RangeTblEntry *) node;
(*rangeTableList) = lappend(*rangeTableList, rangeTable);
}
else if (IsA(node, Query))
{
walkIsComplete = query_tree_walker((Query *) node, ExtractRangeTableEntryWalker,
rangeTableList, QTW_EXAMINE_RTES);
}
else
{
walkIsComplete = expression_tree_walker(node, ExtractRangeTableEntryWalker,
rangeTableList);
}
return walkIsComplete;
}
/*
* DistributedQueryShardList prunes the shards for the table in the query based
* on the query's restriction qualifiers, and returns this list.
*/
static List *
DistributedQueryShardList(Query *query)
{
Oid distributedTableId = ExtractFirstDistributedTableId(query);
List *restrictClauseList = QueryRestrictList(query);
List *shardIntervalList = LookupShardIntervalList(distributedTableId);
List *prunedShardList = PruneShardList(distributedTableId, restrictClauseList,
shardIntervalList);
return prunedShardList;
}
/* Returns true if the query is a select query that reads data from multiple shards. */
static bool
SelectFromMultipleShards(Query *query, List *queryShardList)
{
if ((query->commandType == CMD_SELECT) && (list_length(queryShardList) > 1))
{
return true;
}
else
{
return false;
}
}
/*
* PlanSequentialScan attempts to plan the given query using only a sequential
* scan of the underlying table. The function disables index scan types and
* plans the query. If the plan still contains a non-sequential scan plan node,
* the function errors out.
*/
static PlannedStmt *
PlanSequentialScan(Query *query, int cursorOptions, ParamListInfo boundParams)
{
PlannedStmt *sequentialScanPlan = NULL;
bool indexScanEnabledOldValue = false;
bool bitmapScanEnabledOldValue = false;
Query *queryCopy = NULL;
List *rangeTableList = NIL;
ListCell *rangeTableCell = NULL;
/* error out if the table is a foreign table */
ExtractRangeTableEntryWalker((Node *) query, &rangeTableList);
foreach(rangeTableCell, rangeTableList)
{
RangeTblEntry *rangeTableEntry = (RangeTblEntry *) lfirst(rangeTableCell);
if (rangeTableEntry->rtekind == RTE_RELATION)
{
if (rangeTableEntry->relkind == RELKIND_FOREIGN_TABLE)
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("select from multiple shards is unsupported "
"for foreign tables")));
}
}
}
/* disable index scan types */
indexScanEnabledOldValue = enable_indexscan;
bitmapScanEnabledOldValue = enable_bitmapscan;
enable_indexscan = false;
enable_bitmapscan = false;
queryCopy = copyObject(query);
sequentialScanPlan = standard_planner(queryCopy, cursorOptions, boundParams);
enable_indexscan = indexScanEnabledOldValue;
enable_bitmapscan = bitmapScanEnabledOldValue;
return sequentialScanPlan;
}
/*
* RowAndColumnFilterQuery builds a query which contains the filter clauses from
* the original query and also only selects columns needed for the original
* query. This new query can then be pushed down to the worker nodes.
*/
static Query *
RowAndColumnFilterQuery(Query *query)
{
Query *filterQuery = NULL;
List *rangeTableList = NIL;
List *whereClauseList = NIL;
List *whereClauseColumnList = NIL;
List *projectColumnList = NIL;
List *columnList = NIL;
ListCell *columnCell = NULL;
List *uniqueColumnList = NIL;
List *targetList = NIL;
FromExpr *fromExpr = NULL;
PVCAggregateBehavior aggregateBehavior = PVC_RECURSE_AGGREGATES;
PVCPlaceHolderBehavior placeHolderBehavior = PVC_REJECT_PLACEHOLDERS;
ExtractRangeTableEntryWalker((Node *) query, &rangeTableList);
Assert(list_length(rangeTableList) == 1);
/* build the where-clause expression */
whereClauseList = QueryRestrictList(query);
fromExpr = makeNode(FromExpr);
fromExpr->quals = (Node *) make_ands_explicit((List *) whereClauseList);
fromExpr->fromlist = QueryFromList(rangeTableList);
/* extract columns from both the where and projection clauses */
whereClauseColumnList = pull_var_clause((Node *) fromExpr, aggregateBehavior,
placeHolderBehavior);
projectColumnList = pull_var_clause((Node *) query->targetList, aggregateBehavior,
placeHolderBehavior);
columnList = list_union(whereClauseColumnList, projectColumnList);
/*
* list_union() filters duplicates, but only between the lists. For example,
* if we have a where clause like (where order_id = 1 OR order_id = 2), we
* end up with two order_id columns. We therefore de-dupe the columns here.
*/
foreach(columnCell, columnList)
{
Var *column = (Var *) lfirst(columnCell);
uniqueColumnList = list_append_unique(uniqueColumnList, column);
}
/*
* If the query is a simple "SELECT count(*)", add a NULL constant. This
* constant deparses to "SELECT NULL FROM ...". postgres_fdw generates a
* similar string when no columns are selected.
*/
if (uniqueColumnList == NIL)
{
/* values for NULL const taken from parse_node.c */
Const *nullConst = makeConst(UNKNOWNOID, -1, InvalidOid, -2,
(Datum) 0, true, false);
uniqueColumnList = lappend(uniqueColumnList, nullConst);
}
targetList = TargetEntryList(uniqueColumnList);
filterQuery = makeNode(Query);
filterQuery->commandType = CMD_SELECT;
filterQuery->rtable = rangeTableList;
filterQuery->targetList = targetList;
filterQuery->jointree = fromExpr;
return filterQuery;
}
/*
* QueryRestrictList returns the restriction clauses for the query. For a SELECT
* statement these are the where-clause expressions. For INSERT statements we
* build an equality clause based on the partition-column and its supplied
* insert value.
*/
static List *
QueryRestrictList(Query *query)
{
List *queryRestrictList = NIL;
CmdType commandType = query->commandType;
if (commandType == CMD_INSERT)
{
/* build equality expression based on partition column value for row */
Oid distributedTableId = ExtractFirstDistributedTableId(query);
Var *partitionColumn = PartitionColumn(distributedTableId);
Const *partitionValue = ExtractPartitionValue(query, partitionColumn);
OpExpr *equalityExpr = MakeOpExpression(partitionColumn, BTEqualStrategyNumber);
Node *rightOp = get_rightop((Expr *) equalityExpr);
Const *rightConst = (Const *) rightOp;
Assert(IsA(rightOp, Const));
rightConst->constvalue = partitionValue->constvalue;
rightConst->constisnull = partitionValue->constisnull;
rightConst->constbyval = partitionValue->constbyval;
queryRestrictList = list_make1(equalityExpr);
}
else if (commandType == CMD_SELECT || commandType == CMD_UPDATE ||
commandType == CMD_DELETE)
{
query_tree_walker(query, ExtractFromExpressionWalker, &queryRestrictList, 0);
}
return queryRestrictList;
}
/*
* ExtractPartitionValue extracts the partition column value from a the target
* of a modification command. If a partition value is not a constant, is NULL,
* or is missing altogether, this function throws an error.
*/
static Const *
ExtractPartitionValue(Query *query, Var *partitionColumn)
{
Const *partitionValue = NULL;
TargetEntry *targetEntry = get_tle_by_resno(query->targetList,
partitionColumn->varattno);
if (targetEntry != NULL)
{
if (!IsA(targetEntry->expr, Const))
{
ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot plan INSERT to a distributed table "
"using a non-constant partition column value")));
}
partitionValue = (Const *) targetEntry->expr;
}
if (partitionValue == NULL || partitionValue->constisnull)
{
ereport(ERROR, (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
errmsg("cannot plan INSERT using row with NULL value "
"in partition column")));
}
return partitionValue;
}
/*
* ExtractFromExpressionWalker walks over a FROM expression, and finds all
* explicit qualifiers in the expression.
*/
static bool
ExtractFromExpressionWalker(Node *node, List **qualifierList)
{
bool walkIsComplete = false;
if (node == NULL)
{
return false;
}
if (IsA(node, FromExpr))
{
FromExpr *fromExpression = (FromExpr *) node;
List *fromQualifierList = (List *) fromExpression->quals;
(*qualifierList) = list_concat(*qualifierList, fromQualifierList);
}
walkIsComplete = expression_tree_walker(node, ExtractFromExpressionWalker,
(void *) qualifierList);
return walkIsComplete;
}
/*
* QueryFromList creates the from list construct that is used for building the
* query's join tree. The function creates the from list by making a range table
* reference for each entry in the given range table list.
*/
static List *
QueryFromList(List *rangeTableList)
{
List *fromList = NIL;
Index rangeTableIndex = 1;
uint32 rangeTableCount = (uint32) list_length(rangeTableList);
for (rangeTableIndex = 1; rangeTableIndex <= rangeTableCount; rangeTableIndex++)
{
RangeTblRef *rangeTableReference = makeNode(RangeTblRef);
rangeTableReference->rtindex = rangeTableIndex;
fromList = lappend(fromList, rangeTableReference);
}
return fromList;
}
/*
* TargetEntryList creates a target entry for each expression in the given list,
* and returns the newly created target entries in a list.
*/
static List *
TargetEntryList(List *expressionList)
{
List *targetEntryList = NIL;
ListCell *expressionCell = NULL;
foreach(expressionCell, expressionList)
{
Expr *expression = (Expr *) lfirst(expressionCell);
TargetEntry *targetEntry = makeTargetEntry(expression, -1, NULL, false);
targetEntryList = lappend(targetEntryList, targetEntry);
}
return targetEntryList;
}
/*
* CreateTemporaryTableLikeStmt returns a CreateStmt node which will create a
* clone of the given relation using the CREATE TEMPORARY TABLE LIKE option.
* Note that the function only creates the table, and doesn't copy over indexes,
* constraints, or default values.
*/
static CreateStmt *
CreateTemporaryTableLikeStmt(Oid sourceRelationId)
{
static unsigned long temporaryTableId = 0;
CreateStmt *createStmt = NULL;
StringInfo clonedTableName = NULL;
RangeVar *clonedRelation = NULL;
char *sourceTableName = get_rel_name(sourceRelationId);
Oid sourceSchemaId = get_rel_namespace(sourceRelationId);
char *sourceSchemaName = get_namespace_name(sourceSchemaId);
RangeVar *sourceRelation = makeRangeVar(sourceSchemaName, sourceTableName, -1);
TableLikeClause *tableLikeClause = makeNode(TableLikeClause);
tableLikeClause->relation = sourceRelation;
tableLikeClause->options = 0; /* don't copy over indexes/constraints etc */
/* create a unique name for the cloned table */
clonedTableName = makeStringInfo();
appendStringInfo(clonedTableName, "%s_%d_%lu",
TEMPORARY_TABLE_PREFIX, MyProcPid, temporaryTableId);
temporaryTableId++;
clonedRelation = makeRangeVar(NULL, clonedTableName->data, -1);
clonedRelation->relpersistence = RELPERSISTENCE_TEMP;
createStmt = makeNode(CreateStmt);
createStmt->relation = clonedRelation;
createStmt->tableElts = list_make1(tableLikeClause);
return createStmt;
}
/*
* BuildDistributedPlan simply creates the DistributedPlan instance from the
* provided query and shard interval list.
*/
static DistributedPlan *
BuildDistributedPlan(Query *query, List *shardIntervalList)
{
ListCell *shardIntervalCell = NULL;
List *taskList = NIL;
DistributedPlan *distributedPlan = palloc0(sizeof(DistributedPlan));
distributedPlan->plan.type = (NodeTag) T_DistributedPlan;
distributedPlan->targetList = query->targetList;
foreach(shardIntervalCell, shardIntervalList)
{
ShardInterval *shardInterval = (ShardInterval *) lfirst(shardIntervalCell);
int64 shardId = shardInterval->id;
List *finalizedPlacementList = LoadFinalizedShardPlacementList(shardId);
Task *task = NULL;
StringInfo queryString = makeStringInfo();
/*
* Convert the qualifiers to an explicitly and'd clause, which is needed
* before we deparse the query. This applies to SELECT, UPDATE and
* DELETE statements.
*/
FromExpr *joinTree = query->jointree;
if ((joinTree != NULL) && (joinTree->quals != NULL))
{
Node *whereClause = joinTree->quals;
if (IsA(whereClause, List))
{
joinTree->quals = (Node *) make_ands_explicit((List *) whereClause);
}
}
deparse_shard_query(query, shardId, queryString);
task = (Task *) palloc0(sizeof(Task));
task->queryString = queryString;
task->taskPlacementList = finalizedPlacementList;
task->shardId = shardId;
taskList = lappend(taskList, task);
}
distributedPlan->taskList = taskList;
return distributedPlan;
}
/*
* PgShardExecutorStart sets up the executor state and queryDesc for pgShard
* executed statements. The function also handles multi-shard selects
* differently by fetching the remote data and modifying the existing plan to
* scan that data.
*/
static void
PgShardExecutorStart(QueryDesc *queryDesc, int eflags)
{
PlannedStmt *plannedStatement = queryDesc->plannedstmt;
bool pgShardExecution = IsPgShardPlan(plannedStatement);
if (pgShardExecution)
{
DistributedPlan *distributedPlan = (DistributedPlan *) plannedStatement->planTree;
bool selectFromMultipleShards = distributedPlan->selectFromMultipleShards;
if (!selectFromMultipleShards)
{
bool topLevel = true;
LOCKMODE lockMode = NoLock;
EState *executorState = NULL;
/* disallow transactions and triggers during distributed commands */
PreventTransactionChain(topLevel, "distributed commands");
eflags |= EXEC_FLAG_SKIP_TRIGGERS;
/* build empty executor state to obtain per-query memory context */
executorState = CreateExecutorState();
executorState->es_top_eflags = eflags;
executorState->es_instrument = queryDesc->instrument_options;
queryDesc->estate = executorState;
lockMode = CommutativityRuleToLockMode(plannedStatement->commandType);
if (lockMode != NoLock)
{
AcquireExecutorShardLocks(distributedPlan->taskList, lockMode);
}
}
else
{
/*
* If its a SELECT query over multiple shards, we fetch the relevant
* data from the remote nodes and insert it into a temp table. We then
* point the existing plan to scan this temp table instead of the
* original one.
*/
Plan *originalPlan = NULL;
RangeTblEntry *sequentialScanRangeTable = NULL;
Oid intermediateResultTableId = InvalidOid;
bool missingOK = false;
/* execute the previously created statement to create a temp table */
CreateStmt *createStmt = distributedPlan->createTemporaryTableStmt;
const char *queryDescription = "create temp table like";
RangeVar *intermediateResultTable = createStmt->relation;
ProcessUtility((Node *) createStmt, queryDescription,
PROCESS_UTILITY_TOPLEVEL, NULL, None_Receiver, NULL);
/* execute select queries and fetch results into the temp table */
ExecuteMultipleShardSelect(distributedPlan, intermediateResultTable);
/* update the query descriptor snapshot so results are visible */
UnregisterSnapshot(queryDesc->snapshot);
UpdateActiveSnapshotCommandId();
queryDesc->snapshot = RegisterSnapshot(GetActiveSnapshot());
/* update sequential scan's table entry to point to intermediate table */
intermediateResultTableId = RangeVarGetRelid(intermediateResultTable,
NoLock, missingOK);
Assert(list_length(plannedStatement->rtable) == 1);
sequentialScanRangeTable = linitial(plannedStatement->rtable);
Assert(sequentialScanRangeTable->rtekind == RTE_RELATION);
sequentialScanRangeTable->relid = intermediateResultTableId;
/* swap in modified (local) plan for compatibility with standard start hook */
originalPlan = distributedPlan->originalPlan;
plannedStatement->planTree = originalPlan;