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clickhousedb_fdw.c
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/*-------------------------------------------------------------------------
*
* clickhousedb_fdw.c
* Foreign-data wrapper for remote ClickHouse servers
*
* Portions Copyright (c) 2012-2018, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/clickhousedb_fdw/clickhousedb_fdw.c
*
*-------------------------------------------------------------------------
*/
/* PosrgreSQL main header file */
#include "postgres.h"
/* Clickhouse client library header file */
#include "lib/clickhouse-client.h"
/* Clikhouse FDW main header file */
#include "clickhousedb_fdw.h"
#include "access/htup_details.h"
#include "access/sysattr.h"
#include "catalog/pg_class.h"
#include "commands/defrem.h"
#include "commands/explain.h"
#include "commands/vacuum.h"
#include "foreign/fdwapi.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "nodes/makefuncs.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/cost.h"
#include "optimizer/clauses.h"
#include "optimizer/pathnode.h"
#include "optimizer/paths.h"
#include "optimizer/planmain.h"
#include "optimizer/restrictinfo.h"
#include "optimizer/var.h"
#include "optimizer/tlist.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/sampling.h"
#include "utils/selfuncs.h"
#include "utils/datetime.h"
PG_MODULE_MAGIC;
/* Default CPU cost to start up a foreign query. */
#define DEFAULT_FDW_STARTUP_COST 100.0
/* Default CPU cost to process 1 row (above and beyond cpu_tuple_cost). */
#define DEFAULT_FDW_TUPLE_COST 0.01
/* If no remote estimates, assume a sort costs 20% extra */
#define DEFAULT_FDW_SORT_MULTIPLIER 1.2
/*
* Indexes of FDW-private information stored in fdw_private lists.
*
* These items are indexed with the enum FdwScanPrivateIndex, so an item
* can be fetched with list_nth(). For example, to get the SELECT statement:
* sql = strVal(list_nth(fdw_private, FdwScanPrivateSelectSql));
*/
enum FdwScanPrivateIndex
{
/* SQL statement to execute remotely (as a String node) */
FdwScanPrivateSelectSql,
/* Integer list of attribute numbers retrieved by the SELECT */
FdwScanPrivateRetrievedAttrs,
/* Integer representing the desired fetch_size */
FdwScanPrivateFetchSize,
/*
* String describing join i.e. names of relations being joined and types
* of join, added when the scan is join
*/
FdwScanPrivateRelations
};
/*
* Similarly, this enum describes what's kept in the fdw_private list for
* a ModifyTable node referencing a postgres_fdw foreign table. We store:
*
* 1) INSERT statement text to be sent to the remote server
* 2) Integer list of target attribute numbers for INSERT
*/
enum FdwModifyPrivateIndex
{
/* SQL statement to execute remotely (as a String node) */
FdwModifyPrivateUpdateSql,
/* Integer list of target attribute numbers for INSERT/UPDATE */
FdwModifyPrivateTargetAttnums,
/* has-returning flag (as an integer Value node) */
FdwModifyPrivateHasReturning,
/* Integer list of attribute numbers retrieved by RETURNING */
FdwModifyPrivateRetrievedAttrs
};
/*
* Execution state of a foreign scan using postgres_fdw.
*/
typedef struct ChFdwScanState
{
Relation rel; /* relcache entry for the foreign table. NULL
* for a foreign join scan. */
TupleDesc tupdesc; /* tuple descriptor of scan */
AttInMetadata *attinmeta; /* attribute datatype conversion metadata */
/* extracted fdw_private data */
char *query; /* text of SELECT command */
List *retrieved_attrs; /* list of retrieved attribute numbers */
/* for remote query execution */
Conn *conn; /* connection for the scan */
int numParams; /* number of parameters passed to query */
FmgrInfo *param_flinfo; /* output conversion functions for them */
List *param_exprs; /* executable expressions for param values */
const char **param_values; /* textual values of query parameters */
bool executed;
/* for storing result tuples */
HeapTuple tuples; /* array of currently-retrieved tuples */
/* working memory contexts */
MemoryContext batch_cxt; /* context holding current batch of tuples */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
int fetch_size; /* number of tuples per fetch */
} ChFdwScanState;
/*
* Execution state of a foreign insert.
*/
typedef struct CHFdwModifyState
{
Relation rel; /* relcache entry for the foreign table */
AttInMetadata *attinmeta; /* attribute datatype conversion metadata */
/* for remote query execution */
Conn *conn; /* connection for the scan */
char *p_name; /* name of prepared statement, if created */
/* extracted fdw_private data */
char *query; /* text of INSERT/UPDATE/DELETE command */
List *target_attrs; /* list of target attribute numbers */
List *retrieved_attrs; /* attr numbers retrieved by RETURNING */
/* info about parameters for prepared statement */
AttrNumber ctidAttno; /* attnum of input resjunk ctid column */
int p_nums; /* number of parameters to transmit */
FmgrInfo *p_flinfo; /* output conversion functions for them */
/* working memory context */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
} CHFdwModifyState;
/*
* Workspace for analyzing a foreign table.
*/
typedef struct CHFdwAnalyzeState
{
Relation rel; /* relcache entry for the foreign table */
AttInMetadata *attinmeta; /* attribute datatype conversion metadata */
List *retrieved_attrs; /* attr numbers retrieved by query */
/* collected sample rows */
HeapTuple *rows; /* array of size targrows */
int targrows; /* target # of sample rows */
int numrows; /* # of sample rows collected */
/* for random sampling */
double samplerows; /* # of rows fetched */
double rowstoskip; /* # of rows to skip before next sample */
ReservoirStateData rstate; /* state for reservoir sampling */
/* working memory contexts */
MemoryContext anl_cxt; /* context for per-analyze lifespan data */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
} CHFdwAnalyzeState;
/*
* Identify the attribute where data conversion fails.
*/
typedef struct ConversionLocation
{
Relation rel; /* foreign table's relcache entry. */
AttrNumber cur_attno; /* attribute number being processed, or 0 */
/*
* In case of foreign join push down, fdw_scan_tlist is used to identify
* the Var node corresponding to the error location and
* fsstate->ss.ps.state gives access to the RTEs of corresponding relation
* to get the relation name and attribute name.
*/
ForeignScanState *fsstate;
} ConversionLocation;
/* Callback argument for ec_member_matches_foreign */
typedef struct
{
Expr *current; /* current expr, or NULL if not yet found */
List *already_used; /* expressions already dealt with */
} ec_member_foreign_arg;
/*
* SQL functions
*/
PG_FUNCTION_INFO_V1(clickhousedb_fdw_handler);
extern PGDLLEXPORT void _PG_init(void);
/*
* FDW callback routines
*/
static void clickhouseGetForeignRelSize(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid);
static void clickhouseGetForeignPaths(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid);
static ForeignScan *clickhouseGetForeignPlan(PlannerInfo *root,
RelOptInfo *foreignrel,
Oid foreigntableid,
ForeignPath *best_path,
List *tlist,
List *scan_clauses,
Plan *outer_plan);
static int
clickhouseAcquireSampleRowsFunc(Relation relation, int elevel,
HeapTuple *rows, int targrows,
double *totalrows,
double *totaldeadrows);
static void clickhouseBeginForeignScan(ForeignScanState *node, int eflags);
static TupleTableSlot *clickhouseIterateForeignScan(ForeignScanState *node);
static void clickhouseReScanForeignScan(ForeignScanState *node);
static void clickhouseEndForeignScan(ForeignScanState *node);
static List *clickhousePlanForeignModify(PlannerInfo *root,
ModifyTable *plan,
Index resultRelation,
int subplan_index);
static void clickhouseBeginForeignModify(ModifyTableState *mtstate,
ResultRelInfo *resultRelInfo,
List *fdw_private,
int subplan_index,
int eflags);
static TupleTableSlot *clickhouseExecForeignInsert(EState *estate,
ResultRelInfo *resultRelInfo,
TupleTableSlot *slot,
TupleTableSlot *planSlot);
static void clickhouseBeginForeignInsert(ModifyTableState *mtstate,
ResultRelInfo *resultRelInfo);
static void clickhouseEndForeignInsert(EState *estate,
ResultRelInfo *resultRelInfo);
static void clickhouseExplainForeignScan(ForeignScanState *node,
ExplainState *es);
static void clickhouseGetForeignUpperPaths(PlannerInfo *root,
UpperRelationKind stage,
RelOptInfo *input_rel, RelOptInfo *output_rel,
void *extra);
static bool clickhouseAnalyzeForeignTable(Relation relation,
AcquireSampleRowsFunc *func,
BlockNumber *totalpages);
static void clickhouseGetForeignJoinPaths(PlannerInfo *root,
RelOptInfo *joinrel,
RelOptInfo *outerrel,
RelOptInfo *innerrel,
JoinType jointype,
JoinPathExtraData *extra);
static bool clickhouseRecheckForeignScan(ForeignScanState *node,
TupleTableSlot *slot);
/*
* Helper functions
*/
static void estimate_path_cost_size(PlannerInfo *root,
RelOptInfo *foreignrel,
List *param_join_conds,
List *pathkeys,
double *p_rows, int *p_width,
Cost *p_startup_cost, Cost *p_total_cost);
static bool ec_member_matches_foreign(PlannerInfo *root, RelOptInfo *rel,
EquivalenceClass *ec, EquivalenceMember *em,
void *arg);
static bool fetch_more_data(ForeignScanState *node);
static CHFdwModifyState *create_foreign_modify(EState *estate,
RangeTblEntry *rte,
ResultRelInfo *resultRelInfo,
CmdType operation,
Plan *subplan,
char *query,
List *target_attrs,
bool has_returning,
List *retrieved_attrs);
static void prepare_foreign_modify(TupleTableSlot *slot,
CHFdwModifyState *fmstate);
static const char **convert_prep_stmt_params(CHFdwModifyState *fmstate,
ItemPointer tupleid,
TupleTableSlot *slot);
static void finish_foreign_modify(CHFdwModifyState *fmstate);
static void prepare_query_params(PlanState *node,
List *fdw_exprs,
int numParams,
FmgrInfo **param_flinfo,
List **param_exprs,
const char ***param_values);
static void process_query_params(ExprContext *econtext,
FmgrInfo *param_flinfo,
List *param_exprs,
const char **param_values);
static int postgresAcquireSampleRowsFunc(Relation relation, int elevel,
HeapTuple *rows, int targrows,
double *totalrows,
double *totaldeadrows);
static void analyze_row_processor(Conn *conn, int row,
CHFdwAnalyzeState *astate);
static HeapTuple make_tuple_from_result_row(Conn *conn,
int row,
Relation rel,
AttInMetadata *attinmeta,
List *retrieved_attrs,
ForeignScanState *fsstate,
MemoryContext temp_context,
char *query);
static void conversion_error_callback(void *arg);
static bool foreign_join_ok(PlannerInfo *root, RelOptInfo *joinrel,
JoinType jointype, RelOptInfo *outerrel, RelOptInfo *innerrel,
JoinPathExtraData *extra);
static bool foreign_grouping_ok(PlannerInfo *root, RelOptInfo *grouped_rel,
Node *havingQual);
static List *get_useful_pathkeys_for_relation(PlannerInfo *root,
RelOptInfo *rel);
static List *get_useful_ecs_for_relation(PlannerInfo *root, RelOptInfo *rel);
static void add_paths_with_pathkeys_for_rel(PlannerInfo *root, RelOptInfo *rel,
Path *epq_path);
static void add_foreign_grouping_paths(PlannerInfo *root,
RelOptInfo *input_rel,
RelOptInfo *grouped_rel,
GroupPathExtraData *extra);
static void apply_server_options(CHFdwRelationInfo *fpinfo);
static void apply_table_options(CHFdwRelationInfo *fpinfo);
static void merge_fdw_options(CHFdwRelationInfo *fpinfo,
const CHFdwRelationInfo *fpinfo_o,
const CHFdwRelationInfo *fpinfo_i);
static bool is_join_pushdown_safe = true;
void
_PG_init(void)
{
DefineCustomBoolVariable("clickhousedb_fdw.join_pushdown_safe",
"Server-side join_pushdown_safe",
NULL,
&is_join_pushdown_safe,
false,
PGC_USERSET,
0,
NULL,
NULL,
NULL);
}
/*
* Foreign-data wrapper handler function: return a struct with pointers
* to my callback routines.
*/
Datum
clickhousedb_fdw_handler(PG_FUNCTION_ARGS)
{
FdwRoutine *routine = makeNode(FdwRoutine);
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
/* Functions for scanning foreign tables */
routine->GetForeignRelSize = clickhouseGetForeignRelSize;
routine->GetForeignPaths = clickhouseGetForeignPaths;
routine->GetForeignPlan = clickhouseGetForeignPlan;
routine->BeginForeignScan = clickhouseBeginForeignScan;
routine->IterateForeignScan = clickhouseIterateForeignScan;
routine->ReScanForeignScan = clickhouseReScanForeignScan;
routine->EndForeignScan = clickhouseEndForeignScan;
/* Functions for updating foreign tables */
routine->PlanForeignModify = clickhousePlanForeignModify;
routine->BeginForeignModify = clickhouseBeginForeignModify;
routine->ExecForeignInsert = clickhouseExecForeignInsert;
routine->BeginForeignInsert = clickhouseBeginForeignInsert;
routine->EndForeignInsert = clickhouseEndForeignInsert;
/* Function for EvalPlanQual rechecks */
routine->RecheckForeignScan = clickhouseRecheckForeignScan;
/* Support functions for EXPLAIN */
routine->ExplainForeignScan = clickhouseExplainForeignScan;
/* Support functions for ANALYZE */
routine->AnalyzeForeignTable = clickhouseAnalyzeForeignTable;
/* Support functions for join push-down */
routine->GetForeignJoinPaths = clickhouseGetForeignJoinPaths;
/* Support functions for upper relation push-down */
routine->GetForeignUpperPaths = clickhouseGetForeignUpperPaths;
elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
PG_RETURN_POINTER(routine);
}
/*
* clickhouseGetForeignRelSize
* Estimate # of rows and width of the result of the scan
*
* We should consider the effect of all baserestrictinfo clauses here, but
* not any join clauses.
*/
static void
clickhouseGetForeignRelSize(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid)
{
CHFdwRelationInfo *fpinfo;
ListCell *lc;
RangeTblEntry *rte = planner_rt_fetch(baserel->relid, root);
char *refname;
char *relname;
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
/*
* We use CHFdwRelationInfo to pass various information to subsequent
* functions.
*/
fpinfo = (CHFdwRelationInfo *) palloc0(sizeof(CHFdwRelationInfo));
baserel->fdw_private = (void *) fpinfo;
/* Base foreign tables need to be pushed down always. */
fpinfo->pushdown_safe = true;
/* Look up foreign-table catalog info. */
fpinfo->table = GetForeignTable(foreigntableid);
fpinfo->server = GetForeignServer(fpinfo->table->serverid);
/*
* Extract user-settable option values. Note that per-table setting of
* use_remote_estimate overrides per-server setting.
*/
fpinfo->fdw_startup_cost = DEFAULT_FDW_STARTUP_COST;
fpinfo->fdw_tuple_cost = DEFAULT_FDW_TUPLE_COST;
fpinfo->shippable_extensions = NIL;
apply_server_options(fpinfo);
apply_table_options(fpinfo);
fpinfo->user = NULL;
/*
* Identify which baserestrictinfo clauses can be sent to the remote
* server and which can't.
*/
classifyConditions(root, baserel, baserel->baserestrictinfo,
&fpinfo->remote_conds, &fpinfo->local_conds);
/*
* Identify which attributes will need to be retrieved from the remote
* server. These include all attrs needed for joins or final output, plus
* all attrs used in the local_conds. (Note: if we end up using a
* parameterized scan, it's possible that some of the join clauses will be
* sent to the remote and thus we wouldn't really need to retrieve the
* columns used in them. Doesn't seem worth detecting that case though.)
*/
fpinfo->attrs_used = NULL;
pull_varattnos((Node *) baserel->reltarget->exprs, baserel->relid,
&fpinfo->attrs_used);
foreach (lc, fpinfo->local_conds)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
pull_varattnos((Node *) rinfo->clause, baserel->relid,
&fpinfo->attrs_used);
}
/*
* Compute the selectivity and cost of the local_conds, so we don't have
* to do it over again for each path. The best we can do for these
* conditions is to estimate selectivity on the basis of local statistics.
*/
fpinfo->local_conds_sel = clauselist_selectivity(root,
fpinfo->local_conds,
baserel->relid,
JOIN_INNER,
NULL);
cost_qual_eval(&fpinfo->local_conds_cost, fpinfo->local_conds, root);
/*
* Set cached relation costs to some negative value, so that we can detect
* when they are set to some sensible costs during one (usually the first)
* of the calls to estimate_path_cost_size().
*/
fpinfo->rel_startup_cost = -1;
fpinfo->rel_total_cost = -1;
/*
* Set the name of relation in fpinfo, while we are constructing it here.
* It will be used to build the string describing the join relation in
* EXPLAIN output. We can't know whether VERBOSE option is specified or
* not, so always schema-qualify the foreign table name.
*/
fpinfo->relation_name = makeStringInfo();
relname = get_rel_name(foreigntableid);
refname = rte->eref->aliasname;
appendStringInfo(fpinfo->relation_name, "%s", quote_identifier(relname));
if (*refname && strcmp(refname, relname) != 0)
appendStringInfo(fpinfo->relation_name, " %s",
quote_identifier(rte->eref->aliasname));
/* No outer and inner relations. */
fpinfo->make_outerrel_subquery = false;
fpinfo->make_innerrel_subquery = false;
fpinfo->lower_subquery_rels = NULL;
/* Set the relation index. */
fpinfo->relation_index = baserel->relid;
elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
}
/*
* get_useful_ecs_for_relation
* Determine which EquivalenceClasses might be involved in useful
* orderings of this relation.
*
* This function is in some respects a mirror image of the core function
* pathkeys_useful_for_merging: for a regular table, we know what indexes
* we have and want to test whether any of them are useful. For a foreign
* table, we don't know what indexes are present on the remote side but
* want to speculate about which ones we'd like to use if they existed.
*
* This function returns a list of potentially-useful equivalence classes,
* but it does not guarantee that an EquivalenceMember exists which contains
* Vars only from the given relation. For example, given ft1 JOIN t1 ON
* ft1.x + t1.x = 0, this function will say that the equivalence class
* containing ft1.x + t1.x is potentially useful. Supposing ft1 is remote and
* t1 is local (or on a different server), it will turn out that no useful
* ORDER BY clause can be generated. It's not our job to figure that out
* here; we're only interested in identifying relevant ECs.
*/
static List *
get_useful_ecs_for_relation(PlannerInfo *root, RelOptInfo *rel)
{
List *useful_eclass_list = NIL;
ListCell *lc;
Relids relids;
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
/*
* First, consider whether any active EC is potentially useful for a merge
* join against this relation.
*/
if (rel->has_eclass_joins)
{
foreach (lc, root->eq_classes)
{
EquivalenceClass *cur_ec = (EquivalenceClass *) lfirst(lc);
if (eclass_useful_for_merging(root, cur_ec, rel))
{
useful_eclass_list = lappend(useful_eclass_list, cur_ec);
}
}
}
/*
* Next, consider whether there are any non-EC derivable join clauses that
* are merge-joinable. If the joininfo list is empty, we can exit
* quickly.
*/
if (rel->joininfo == NIL)
{
return useful_eclass_list;
}
/* If this is a child rel, we must use the topmost parent rel to search. */
if (IS_OTHER_REL(rel))
{
Assert(!bms_is_empty(rel->top_parent_relids));
relids = rel->top_parent_relids;
}
else
{
relids = rel->relids;
}
/* Check each join clause in turn. */
foreach (lc, rel->joininfo)
{
RestrictInfo *restrictinfo = (RestrictInfo *) lfirst(lc);
/* Consider only mergejoinable clauses */
if (restrictinfo->mergeopfamilies == NIL)
{
continue;
}
/* Make sure we've got canonical ECs. */
update_mergeclause_eclasses(root, restrictinfo);
/*
* restrictinfo->mergeopfamilies != NIL is sufficient to guarantee
* that left_ec and right_ec will be initialized, per comments in
* distribute_qual_to_rels.
*
* We want to identify which side of this merge-joinable clause
* contains columns from the relation produced by this RelOptInfo. We
* test for overlap, not containment, because there could be extra
* relations on either side. For example, suppose we've got something
* like ((A JOIN B ON A.x = B.x) JOIN C ON A.y = C.y) LEFT JOIN D ON
* A.y = D.y. The input rel might be the joinrel between A and B, and
* we'll consider the join clause A.y = D.y. relids contains a
* relation not involved in the join class (B) and the equivalence
* class for the left-hand side of the clause contains a relation not
* involved in the input rel (C). Despite the fact that we have only
* overlap and not containment in either direction, A.y is potentially
* useful as a sort column.
*
* Note that it's even possible that relids overlaps neither side of
* the join clause. For example, consider A LEFT JOIN B ON A.x = B.x
* AND A.x = 1. The clause A.x = 1 will appear in B's joininfo list,
* but overlaps neither side of B. In that case, we just skip this
* join clause, since it doesn't suggest a useful sort order for this
* relation.
*/
if (bms_overlap(relids, restrictinfo->right_ec->ec_relids))
useful_eclass_list = list_append_unique_ptr(useful_eclass_list,
restrictinfo->right_ec);
else if (bms_overlap(relids, restrictinfo->left_ec->ec_relids))
useful_eclass_list = list_append_unique_ptr(useful_eclass_list,
restrictinfo->left_ec);
}
elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
return useful_eclass_list;
}
/*
* get_useful_pathkeys_for_relation
* Determine which orderings of a relation might be useful.
*
* Getting data in sorted order can be useful either because the requested
* order matches the final output ordering for the overall query we're
* planning, or because it enables an efficient merge join. Here, we try
* to figure out which pathkeys to consider.
*/
static List *
get_useful_pathkeys_for_relation(PlannerInfo *root, RelOptInfo *rel)
{
List *useful_pathkeys_list = NIL;
List *useful_eclass_list;
CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) rel->fdw_private;
EquivalenceClass *query_ec = NULL;
ListCell *lc;
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
/*
* Pushing the query_pathkeys to the remote server is always worth
* considering, because it might let us avoid a local sort.
*/
if (root->query_pathkeys)
{
bool query_pathkeys_ok = true;
foreach (lc, root->query_pathkeys)
{
PathKey *pathkey = (PathKey *) lfirst(lc);
EquivalenceClass *pathkey_ec = pathkey->pk_eclass;
Expr *em_expr;
/*
* The planner and executor don't have any clever strategy for
* taking data sorted by a prefix of the query's pathkeys and
* getting it to be sorted by all of those pathkeys. We'll just
* end up resorting the entire data set. So, unless we can push
* down all of the query pathkeys, forget it.
*
* is_foreign_expr would detect volatile expressions as well, but
* checking ec_has_volatile here saves some cycles.
*/
if (pathkey_ec->ec_has_volatile ||
!(em_expr = find_em_expr_for_rel(pathkey_ec, rel)) ||
!is_foreign_expr(root, rel, em_expr))
{
query_pathkeys_ok = false;
break;
}
}
if (query_pathkeys_ok)
{
useful_pathkeys_list = list_make1(list_copy(root->query_pathkeys));
}
}
/*
* Even if we're not using remote estimates, having the remote side do the
* sort generally won't be any worse than doing it locally, and it might
* be much better if the remote side can generate data in the right order
* without needing a sort at all. However, what we're going to do next is
* try to generate pathkeys that seem promising for possible merge joins,
* and that's more speculative. A wrong choice might hurt quite a bit, so
* bail out if we can't use remote estimates.
*/
if (!fpinfo->use_remote_estimate)
{
return useful_pathkeys_list;
}
/* Get the list of interesting EquivalenceClasses. */
useful_eclass_list = get_useful_ecs_for_relation(root, rel);
/* Extract unique EC for query, if any, so we don't consider it again. */
if (list_length(root->query_pathkeys) == 1)
{
PathKey *query_pathkey = linitial(root->query_pathkeys);
query_ec = query_pathkey->pk_eclass;
}
/*
* As a heuristic, the only pathkeys we consider here are those of length
* one. It's surely possible to consider more, but since each one we
* choose to consider will generate a round-trip to the remote side, we
* need to be a bit cautious here. It would sure be nice to have a local
* cache of information about remote index definitions...
*/
foreach (lc, useful_eclass_list)
{
EquivalenceClass *cur_ec = lfirst(lc);
Expr *em_expr;
PathKey *pathkey;
/* If redundant with what we did above, skip it. */
if (cur_ec == query_ec)
{
continue;
}
/* If no pushable expression for this rel, skip it. */
em_expr = find_em_expr_for_rel(cur_ec, rel);
if (em_expr == NULL || !is_foreign_expr(root, rel, em_expr))
{
continue;
}
/* Looks like we can generate a pathkey, so let's do it. */
pathkey = make_canonical_pathkey(root, cur_ec,
linitial_oid(cur_ec->ec_opfamilies),
BTLessStrategyNumber,
false);
useful_pathkeys_list = lappend(useful_pathkeys_list,
list_make1(pathkey));
}
elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
return useful_pathkeys_list;
}
/*
* postgresGetForeignPaths
* Create possible scan paths for a scan on the foreign table
*/
static void
clickhouseGetForeignPaths(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid)
{
CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) baserel->fdw_private;
ForeignPath *path;
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
/*
* Create simplest ForeignScan path node and add it to baserel. This path
* corresponds to SeqScan path of regular tables (though depending on what
* baserestrict conditions we were able to send to remote, there might
* actually be an indexscan happening there). We already did all the work
* to estimate cost and size of this path.
*/
path = create_foreignscan_path(root, baserel,
NULL, /* default pathtarget */
fpinfo->rows,
fpinfo->startup_cost,
fpinfo->total_cost,
NIL, /* no pathkeys */
NULL, /* no outer rel either */
NULL, /* no extra plan */
NIL); /* no fdw_private list */
add_path(baserel, (Path *) path);
/* Add paths with pathkeys */
add_paths_with_pathkeys_for_rel(root, baserel, NULL);
elog(DEBUG2, "< %s:%d", __FUNCTION__, __LINE__);
}
/*
* clickhouseGetForeignPlan
* Create ForeignScan plan node which implements selected best path
*/
static ForeignScan *
clickhouseGetForeignPlan(PlannerInfo *root,
RelOptInfo *foreignrel,
Oid foreigntableid,
ForeignPath *best_path,
List *tlist,
List *scan_clauses,
Plan *outer_plan)
{
CHFdwRelationInfo *fpinfo = (CHFdwRelationInfo *) foreignrel->fdw_private;
Index scan_relid;
List *fdw_private;
List *remote_exprs = NIL;
List *local_exprs = NIL;
List *params_list = NIL;
List *fdw_scan_tlist = NIL;
List *fdw_recheck_quals = NIL;
List *retrieved_attrs;
StringInfoData sql;
ListCell *lc;
elog(DEBUG2, "> %s:%d", __FUNCTION__, __LINE__);
if (IS_SIMPLE_REL(foreignrel))
{
/*
* For base relations, set scan_relid as the relid of the relation.
*/
scan_relid = foreignrel->relid;
/*
* In a base-relation scan, we must apply the given scan_clauses.
*
* Separate the scan_clauses into those that can be executed remotely
* and those that can't. baserestrictinfo clauses that were
* previously determined to be safe or unsafe by classifyConditions
* are found in fpinfo->remote_conds and fpinfo->local_conds. Anything
* else in the scan_clauses list will be a join clause, which we have
* to check for remote-safety.
*
* Note: the join clauses we see here should be the exact same ones
* previously examined by postgresGetForeignPaths. Possibly it'd be
* worth passing forward the classification work done then, rather
* than repeating it here.
*
* This code must match "extract_actual_clauses(scan_clauses, false)"
* except for the additional decision about remote versus local
* execution.
*/
foreach (lc, scan_clauses)
{
RestrictInfo *rinfo = lfirst_node(RestrictInfo, lc);
/* Ignore any pseudoconstants, they're dealt with elsewhere */
if (rinfo->pseudoconstant)
{
continue;
}
if (list_member_ptr(fpinfo->remote_conds, rinfo))
{
remote_exprs = lappend(remote_exprs, rinfo->clause);
}
else if (list_member_ptr(fpinfo->local_conds, rinfo))
{
local_exprs = lappend(local_exprs, rinfo->clause);
}
else if (is_foreign_expr(root, foreignrel, rinfo->clause))
{
remote_exprs = lappend(remote_exprs, rinfo->clause);
}
else
{
local_exprs = lappend(local_exprs, rinfo->clause);
}
}
/*
* For a base-relation scan, we have to support EPQ recheck, which
* should recheck all the remote quals.
*/
fdw_recheck_quals = remote_exprs;
}
else
{
/*
* Join relation or upper relation - set scan_relid to 0.
*/
scan_relid = 0;
/*
* For a join rel, baserestrictinfo is NIL and we are not considering
* parameterization right now, so there should be no scan_clauses for
* a joinrel or an upper rel either.
*/
Assert(!scan_clauses);
/*
* Instead we get the conditions to apply from the fdw_private
* structure.
*/
remote_exprs = extract_actual_clauses(fpinfo->remote_conds, false);
local_exprs = extract_actual_clauses(fpinfo->local_conds, false);
/*
* We leave fdw_recheck_quals empty in this case, since we never need
* to apply EPQ recheck clauses. In the case of a joinrel, EPQ
* recheck is handled elsewhere --- see postgresGetForeignJoinPaths().
* If we're planning an upperrel (ie, remote grouping or aggregation)
* then there's no EPQ to do because SELECT FOR UPDATE wouldn't be
* allowed, and indeed we *can't* put the remote clauses into
* fdw_recheck_quals because the unaggregated Vars won't be available
* locally.
*/
/* Build the list of columns to be fetched from the foreign server. */
fdw_scan_tlist = build_tlist_to_deparse(foreignrel);
/*
* Ensure that the outer plan produces a tuple whose descriptor
* matches our scan tuple slot. This is safe because all scans and
* joins support projection, so we never need to insert a Result node.
* Also, remove the local conditions from outer plan's quals, lest
* they will be evaluated twice, once by the local plan and once by
* the scan.
*/
if (outer_plan)
{
ListCell *lc;
/*
* Right now, we only consider grouping and aggregation beyond
* joins. Queries involving aggregates or grouping do not require
* EPQ mechanism, hence should not have an outer plan here.
*/
Assert(!IS_UPPER_REL(foreignrel));
outer_plan->targetlist = fdw_scan_tlist;
foreach (lc, local_exprs)
{
Join *join_plan = (Join *) outer_plan;
Node *qual = lfirst(lc);
outer_plan->qual = list_delete(outer_plan->qual, qual);
/*
* For an inner join the local conditions of foreign scan plan
* can be part of the joinquals as well.
*/
if (join_plan->jointype == JOIN_INNER)
join_plan->joinqual = list_delete(join_plan->joinqual,
qual);
}
}
}
/*
* Build the query string to be sent for execution, and identify
* expressions to be sent as parameters.
*/
initStringInfo(&sql);
deparseSelectStmtForRel(&sql, root, foreignrel, fdw_scan_tlist,
remote_exprs, best_path->path.pathkeys,
false, &retrieved_attrs, ¶ms_list);
/* Remember remote_exprs for possible use by postgresPlanDirectModify */
fpinfo->final_remote_exprs = remote_exprs;
/*
* Build the fdw_private list that will be available to the executor.
* Items in the list must match order in enum FdwScanPrivateIndex.
*/
fdw_private = list_make3(makeString(sql.data),
retrieved_attrs,
makeInteger(fpinfo->fetch_size));
if (IS_JOIN_REL(foreignrel) || IS_UPPER_REL(foreignrel))
fdw_private = lappend(fdw_private,
makeString(fpinfo->relation_name->data));
/*
* Create the ForeignScan node for the given relation.
*
* Note that the remote parameter expressions are stored in the fdw_exprs
* field of the finished plan node; we can't keep them in private state
* because then they wouldn't be subject to later planner processing.
*/
return make_foreignscan(tlist,
local_exprs,
scan_relid,
params_list,
fdw_private,
fdw_scan_tlist,
fdw_recheck_quals,