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postgres_fdw.c
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/*-------------------------------------------------------------------------
*
* postgres_fdw.c
* Foreign-data wrapper for remote PostgreSQL servers
*
* Portions Copyright (c) 2012-2013, PostgreSQL Global Development Group
*
* IDENTIFICATION
* contrib/postgres_fdw/postgres_fdw.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "postgres_fdw.h"
#include "access/htup.h"
#include "commands/defrem.h"
#include "commands/explain.h"
#include "commands/vacuum.h"
#include "foreign/fdwapi.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "optimizer/cost.h"
#include "optimizer/pathnode.h"
#include "optimizer/planmain.h"
#include "parser/parsetree.h"
#include "utils/builtins.h"
#include "utils/guc.h"
#include "utils/lsyscache.h"
#include "utils/memutils.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
/*
* FDW-specific planner information kept in RelOptInfo.fdw_private for a
* foreign table. This information is collected by postgresGetForeignRelSize.
*/
typedef struct PgFdwRelationInfo
{
/* XXX underdocumented, but a lot of this shouldn't be here anyway */
StringInfoData sql;
Cost startup_cost;
Cost total_cost;
List *remote_conds;
List *param_conds;
List *local_conds;
List *param_numbers;
/* Cached catalog information. */
ForeignTable *table;
ForeignServer *server;
} PgFdwRelationInfo;
/*
* Indexes of FDW-private information stored in fdw_private list.
*
* We store various information in ForeignScan.fdw_private to pass it from
* planner to executor. Specifically there is:
*
* 1) SELECT statement text to be sent to the remote server
* 2) IDs of PARAM_EXEC Params used in the SELECT statement
*
* These items are indexed with the enum FdwPrivateIndex, so an item can be
* fetched with list_nth(). For example, to get the SELECT statement:
* sql = strVal(list_nth(fdw_private, FdwPrivateSelectSql));
*/
enum FdwPrivateIndex
{
/* SQL statement to execute remotely (as a String node) */
FdwPrivateSelectSql,
/* Integer list of param IDs of PARAM_EXEC Params used in SQL stmt */
FdwPrivateExternParamIds,
/* # of elements stored in the list fdw_private */
FdwPrivateNum
};
/*
* Execution state of a foreign scan using postgres_fdw.
*/
typedef struct PgFdwExecutionState
{
Relation rel; /* relcache entry for the foreign table */
AttInMetadata *attinmeta; /* attribute datatype conversion metadata */
List *fdw_private; /* FDW-private information from planner */
/* for remote query execution */
PGconn *conn; /* connection for the scan */
unsigned int cursor_number; /* quasi-unique ID for my cursor */
bool cursor_exists; /* have we created the cursor? */
bool extparams_done; /* have we converted PARAM_EXTERN params? */
int numParams; /* number of parameters passed to query */
Oid *param_types; /* array of types of query parameters */
const char **param_values; /* array of values of query parameters */
/* for storing result tuples */
HeapTuple *tuples; /* array of currently-retrieved tuples */
int num_tuples; /* # of tuples in array */
int next_tuple; /* index of next one to return */
/* batch-level state, for optimizing rewinds and avoiding useless fetch */
int fetch_ct_2; /* Min(# of fetches done, 2) */
bool eof_reached; /* true if last fetch reached EOF */
/* working memory contexts */
MemoryContext batch_cxt; /* context holding current batch of tuples */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
} PgFdwExecutionState;
/*
* Workspace for analyzing a foreign table.
*/
typedef struct PgFdwAnalyzeState
{
Relation rel; /* relcache entry for the foreign table */
AttInMetadata *attinmeta; /* attribute datatype conversion metadata */
/* 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 */
double rstate; /* random state */
/* working memory contexts */
MemoryContext anl_cxt; /* context for per-analyze lifespan data */
MemoryContext temp_cxt; /* context for per-tuple temporary data */
} PgFdwAnalyzeState;
/*
* 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 */
} ConversionLocation;
/*
* SQL functions
*/
extern Datum postgres_fdw_handler(PG_FUNCTION_ARGS);
PG_FUNCTION_INFO_V1(postgres_fdw_handler);
/*
* FDW callback routines
*/
static void postgresGetForeignRelSize(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid);
static void postgresGetForeignPaths(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid);
static ForeignScan *postgresGetForeignPlan(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid,
ForeignPath *best_path,
List *tlist,
List *scan_clauses);
static void postgresExplainForeignScan(ForeignScanState *node,
ExplainState *es);
static void postgresBeginForeignScan(ForeignScanState *node, int eflags);
static TupleTableSlot *postgresIterateForeignScan(ForeignScanState *node);
static void postgresReScanForeignScan(ForeignScanState *node);
static void postgresEndForeignScan(ForeignScanState *node);
static bool postgresAnalyzeForeignTable(Relation relation,
AcquireSampleRowsFunc *func,
BlockNumber *totalpages);
/*
* Helper functions
*/
static void get_remote_estimate(const char *sql,
PGconn *conn,
double *rows,
int *width,
Cost *startup_cost,
Cost *total_cost);
static void create_cursor(ForeignScanState *node);
static void fetch_more_data(ForeignScanState *node);
static void close_cursor(PGconn *conn, unsigned int cursor_number);
static int postgresAcquireSampleRowsFunc(Relation relation, int elevel,
HeapTuple *rows, int targrows,
double *totalrows,
double *totaldeadrows);
static void analyze_row_processor(PGresult *res, int row,
PgFdwAnalyzeState *astate);
static HeapTuple make_tuple_from_result_row(PGresult *res,
int row,
Relation rel,
AttInMetadata *attinmeta,
MemoryContext temp_context);
static void conversion_error_callback(void *arg);
/*
* Foreign-data wrapper handler function: return a struct with pointers
* to my callback routines.
*/
Datum
postgres_fdw_handler(PG_FUNCTION_ARGS)
{
FdwRoutine *routine = makeNode(FdwRoutine);
/* Required handler functions. */
routine->GetForeignRelSize = postgresGetForeignRelSize;
routine->GetForeignPaths = postgresGetForeignPaths;
routine->GetForeignPlan = postgresGetForeignPlan;
routine->ExplainForeignScan = postgresExplainForeignScan;
routine->BeginForeignScan = postgresBeginForeignScan;
routine->IterateForeignScan = postgresIterateForeignScan;
routine->ReScanForeignScan = postgresReScanForeignScan;
routine->EndForeignScan = postgresEndForeignScan;
/* Optional handler functions. */
routine->AnalyzeForeignTable = postgresAnalyzeForeignTable;
PG_RETURN_POINTER(routine);
}
/*
* postgresGetForeignRelSize
* Estimate # of rows and width of the result of the scan
*
* Here we estimate number of rows returned by the scan in two steps. In the
* first step, we execute remote EXPLAIN command to obtain the number of rows
* returned from remote side. In the second step, we calculate the selectivity
* of the filtering done on local side, and modify first estimate.
*
* We have to get some catalog objects and generate remote query string here,
* so we store such expensive information in FDW private area of RelOptInfo and
* pass them to subsequent functions for reuse.
*/
static void
postgresGetForeignRelSize(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid)
{
bool use_remote_estimate = false;
ListCell *lc;
PgFdwRelationInfo *fpinfo;
StringInfo sql;
ForeignTable *table;
ForeignServer *server;
Selectivity sel;
double rows;
int width;
Cost startup_cost;
Cost total_cost;
Cost run_cost;
QualCost qpqual_cost;
Cost cpu_per_tuple;
List *remote_conds;
List *param_conds;
List *local_conds;
List *param_numbers;
/*
* We use PgFdwRelationInfo to pass various information to subsequent
* functions.
*/
fpinfo = palloc0(sizeof(PgFdwRelationInfo));
initStringInfo(&fpinfo->sql);
sql = &fpinfo->sql;
/*
* Determine whether we use remote estimate or not. Note that per-table
* setting overrides per-server setting.
*/
table = GetForeignTable(foreigntableid);
server = GetForeignServer(table->serverid);
foreach(lc, server->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "use_remote_estimate") == 0)
{
use_remote_estimate = defGetBoolean(def);
break;
}
}
foreach(lc, table->options)
{
DefElem *def = (DefElem *) lfirst(lc);
if (strcmp(def->defname, "use_remote_estimate") == 0)
{
use_remote_estimate = defGetBoolean(def);
break;
}
}
/*
* Construct remote query which consists of SELECT, FROM, and WHERE
* clauses. Conditions which contain any Param node are excluded because
* placeholder can't be used in EXPLAIN statement. Such conditions are
* appended later.
*/
classifyConditions(root, baserel, &remote_conds, ¶m_conds,
&local_conds, ¶m_numbers);
deparseSimpleSql(sql, root, baserel, local_conds);
if (list_length(remote_conds) > 0)
appendWhereClause(sql, true, remote_conds, root);
/*
* If the table or the server is configured to use remote estimates,
* connect to the foreign server and execute EXPLAIN with the quals that
* don't contain any Param nodes. Otherwise, estimate rows using whatever
* statistics we have locally, in a way similar to ordinary tables.
*/
if (use_remote_estimate)
{
RangeTblEntry *rte;
Oid userid;
UserMapping *user;
PGconn *conn;
/*
* Identify which user to do the remote access as. This should match
* what ExecCheckRTEPerms() does. If we fail due to lack of
* permissions, the query would have failed at runtime anyway.
*/
rte = planner_rt_fetch(baserel->relid, root);
userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
user = GetUserMapping(userid, server->serverid);
conn = GetConnection(server, user);
get_remote_estimate(sql->data, conn, &rows, &width,
&startup_cost, &total_cost);
ReleaseConnection(conn);
/*
* Estimate selectivity of conditions which were not used in remote
* EXPLAIN by calling clauselist_selectivity(). The best we can do
* for these conditions is to estimate selectivity on the basis of
* local statistics.
*/
sel = clauselist_selectivity(root, param_conds,
baserel->relid, JOIN_INNER, NULL);
sel *= clauselist_selectivity(root, local_conds,
baserel->relid, JOIN_INNER, NULL);
/*
* Add in the eval cost of those conditions, too.
*/
cost_qual_eval(&qpqual_cost, param_conds, root);
startup_cost += qpqual_cost.startup;
total_cost += qpqual_cost.per_tuple * rows;
cost_qual_eval(&qpqual_cost, local_conds, root);
startup_cost += qpqual_cost.startup;
total_cost += qpqual_cost.per_tuple * rows;
/* Report estimated numbers to planner. */
baserel->rows = clamp_row_est(rows * sel);
baserel->width = width;
}
else
{
/*
* Estimate rows from the result of the last ANALYZE, using all
* conditions specified in original query.
*
* If the foreign table has never been ANALYZEd, it will have relpages
* and reltuples equal to zero, which most likely has nothing to do
* with reality. We can't do a whole lot about that if we're not
* allowed to consult the remote server, but we can use a hack similar
* to plancat.c's treatment of empty relations: use a minimum size
* estimate of 10 pages, and divide by the column-datatype-based width
* estimate to get the corresponding number of tuples.
*/
if (baserel->pages == 0 && baserel->tuples == 0)
{
baserel->pages = 10;
baserel->tuples =
(10 * BLCKSZ) / (baserel->width + sizeof(HeapTupleHeaderData));
}
set_baserel_size_estimates(root, baserel);
/* Cost as though this were a seqscan, which is pessimistic. */
startup_cost = 0;
run_cost = 0;
run_cost += seq_page_cost * baserel->pages;
startup_cost += baserel->baserestrictcost.startup;
cpu_per_tuple = cpu_tuple_cost + baserel->baserestrictcost.per_tuple;
run_cost += cpu_per_tuple * baserel->tuples;
total_cost = startup_cost + run_cost;
}
/*
* Finish deparsing remote query by adding conditions which were unusable
* in remote EXPLAIN since they contain Param nodes.
*/
if (list_length(param_conds) > 0)
appendWhereClause(sql, !(list_length(remote_conds) > 0), param_conds,
root);
/*
* Store obtained information into FDW-private area of RelOptInfo so it's
* available to subsequent functions.
*/
fpinfo->startup_cost = startup_cost;
fpinfo->total_cost = total_cost;
fpinfo->remote_conds = remote_conds;
fpinfo->param_conds = param_conds;
fpinfo->local_conds = local_conds;
fpinfo->param_numbers = param_numbers;
fpinfo->table = table;
fpinfo->server = server;
baserel->fdw_private = (void *) fpinfo;
}
/*
* postgresGetForeignPaths
* Create possible scan paths for a scan on the foreign table
*/
static void
postgresGetForeignPaths(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid)
{
PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) baserel->fdw_private;
ForeignPath *path;
ListCell *lc;
double fdw_startup_cost = DEFAULT_FDW_STARTUP_COST;
double fdw_tuple_cost = DEFAULT_FDW_TUPLE_COST;
Cost startup_cost;
Cost total_cost;
List *fdw_private;
/*
* Check for user override of fdw_startup_cost, fdw_tuple_cost values
*/
foreach(lc, fpinfo->server->options)
{
DefElem *d = (DefElem *) lfirst(lc);
if (strcmp(d->defname, "fdw_startup_cost") == 0)
fdw_startup_cost = strtod(defGetString(d), NULL);
else if (strcmp(d->defname, "fdw_tuple_cost") == 0)
fdw_tuple_cost = strtod(defGetString(d), NULL);
}
/*
* We have cost values which are estimated on remote side, so adjust them
* for better estimate which respect various stuffs to complete the scan,
* such as sending query, transferring result, and local filtering.
*/
startup_cost = fpinfo->startup_cost;
total_cost = fpinfo->total_cost;
/*----------
* Adjust costs with factors of the corresponding foreign server:
* - add cost to establish connection to both startup and total
* - add cost to manipulate on remote, and transfer result to total
* - add cost to manipulate tuples on local side to total
*----------
*/
startup_cost += fdw_startup_cost;
total_cost += fdw_startup_cost;
total_cost += fdw_tuple_cost * baserel->rows;
total_cost += cpu_tuple_cost * baserel->rows;
/*
* Build the fdw_private list that will be available to the executor.
* Items in the list must match enum FdwPrivateIndex, above.
*/
fdw_private = list_make2(makeString(fpinfo->sql.data),
fpinfo->param_numbers);
/*
* 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).
*/
path = create_foreignscan_path(root, baserel,
baserel->rows,
startup_cost,
total_cost,
NIL, /* no pathkeys */
NULL, /* no outer rel either */
fdw_private);
add_path(baserel, (Path *) path);
/*
* XXX We can consider sorted path or parameterized path here if we know
* that foreign table is indexed on remote end. For this purpose, we
* might have to support FOREIGN INDEX to represent possible sets of sort
* keys and/or filtering. Or we could just try some join conditions and
* see if remote side estimates using them as markedly cheaper. Note that
* executor functions need work to support internal Params before we can
* try generating any parameterized paths, though.
*/
}
/*
* postgresGetForeignPlan
* Create ForeignScan plan node which implements selected best path
*/
static ForeignScan *
postgresGetForeignPlan(PlannerInfo *root,
RelOptInfo *baserel,
Oid foreigntableid,
ForeignPath *best_path,
List *tlist,
List *scan_clauses)
{
PgFdwRelationInfo *fpinfo = (PgFdwRelationInfo *) baserel->fdw_private;
Index scan_relid = baserel->relid;
List *fdw_private = best_path->fdw_private;
List *remote_exprs = NIL;
List *local_exprs = NIL;
ListCell *lc;
/*
* Separate the scan_clauses into those that can be executed remotely and
* those that can't. For now, we accept only remote clauses that were
* previously determined to be safe by classifyClauses (so, only
* baserestrictinfo clauses can be used that way).
*
* 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 = (RestrictInfo *) lfirst(lc);
Assert(IsA(rinfo, RestrictInfo));
/* Ignore any pseudoconstants, they're dealt with elsewhere */
if (rinfo->pseudoconstant)
continue;
/* Either simple or parameterized remote clauses are OK now */
if (list_member_ptr(fpinfo->remote_conds, rinfo) ||
list_member_ptr(fpinfo->param_conds, rinfo))
remote_exprs = lappend(remote_exprs, rinfo->clause);
else
local_exprs = lappend(local_exprs, rinfo->clause);
}
/*
* Create the ForeignScan node from target list, local filtering
* expressions, remote filtering expressions, and FDW private information.
*
* Note that the remote_exprs 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.
*
* XXX Currently, the remote_exprs aren't actually used at runtime, so we
* don't need to store them at all. But we'll keep this behavior for a
* little while for debugging reasons.
*/
return make_foreignscan(tlist,
local_exprs,
scan_relid,
remote_exprs,
fdw_private);
}
/*
* postgresExplainForeignScan
* Produce extra output for EXPLAIN
*/
static void
postgresExplainForeignScan(ForeignScanState *node, ExplainState *es)
{
List *fdw_private;
char *sql;
if (es->verbose)
{
fdw_private = ((ForeignScan *) node->ss.ps.plan)->fdw_private;
sql = strVal(list_nth(fdw_private, FdwPrivateSelectSql));
ExplainPropertyText("Remote SQL", sql, es);
}
}
/*
* postgresBeginForeignScan
* Initiate an executor scan of a foreign PostgreSQL table.
*/
static void
postgresBeginForeignScan(ForeignScanState *node, int eflags)
{
ForeignScan *fsplan = (ForeignScan *) node->ss.ps.plan;
EState *estate = node->ss.ps.state;
PgFdwExecutionState *festate;
RangeTblEntry *rte;
Oid userid;
ForeignTable *table;
ForeignServer *server;
UserMapping *user;
List *param_numbers;
int numParams;
int i;
/*
* Do nothing in EXPLAIN (no ANALYZE) case. node->fdw_state stays NULL.
*/
if (eflags & EXEC_FLAG_EXPLAIN_ONLY)
return;
/*
* We'll save private state in node->fdw_state.
*/
festate = (PgFdwExecutionState *) palloc0(sizeof(PgFdwExecutionState));
node->fdw_state = (void *) festate;
/*
* Identify which user to do the remote access as. This should match what
* ExecCheckRTEPerms() does.
*/
rte = rt_fetch(fsplan->scan.scanrelid, estate->es_range_table);
userid = rte->checkAsUser ? rte->checkAsUser : GetUserId();
/* Get info about foreign table. */
festate->rel = node->ss.ss_currentRelation;
table = GetForeignTable(RelationGetRelid(festate->rel));
server = GetForeignServer(table->serverid);
user = GetUserMapping(userid, server->serverid);
/*
* Get connection to the foreign server. Connection manager will
* establish new connection if necessary.
*/
festate->conn = GetConnection(server, user);
/* Assign a unique ID for my cursor */
festate->cursor_number = GetCursorNumber(festate->conn);
festate->cursor_exists = false;
/* Get private info created by planner functions. */
festate->fdw_private = fsplan->fdw_private;
/* Create contexts for batches of tuples and per-tuple temp workspace. */
festate->batch_cxt = AllocSetContextCreate(estate->es_query_cxt,
"postgres_fdw tuple data",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
festate->temp_cxt = AllocSetContextCreate(estate->es_query_cxt,
"postgres_fdw temporary data",
ALLOCSET_SMALL_MINSIZE,
ALLOCSET_SMALL_INITSIZE,
ALLOCSET_SMALL_MAXSIZE);
/* Get info we'll need for data conversion. */
festate->attinmeta = TupleDescGetAttInMetadata(RelationGetDescr(festate->rel));
/*
* Allocate buffer for query parameters, if the remote conditions use any.
*
* We use a parameter slot for each PARAM_EXTERN parameter, even though
* not all of them may get sent to the remote server. This allows us to
* refer to Params by their original number rather than remapping, and it
* doesn't cost much. Slots that are not actually used get filled with
* null values that are arbitrarily marked as being of type int4.
*/
param_numbers = (List *)
list_nth(festate->fdw_private, FdwPrivateExternParamIds);
if (param_numbers != NIL)
{
ParamListInfo params = estate->es_param_list_info;
numParams = params ? params->numParams : 0;
}
else
numParams = 0;
festate->numParams = numParams;
if (numParams > 0)
{
/* we initially fill all slots with value = NULL, type = int4 */
festate->param_types = (Oid *) palloc(numParams * sizeof(Oid));
festate->param_values = (const char **) palloc0(numParams * sizeof(char *));
for (i = 0; i < numParams; i++)
festate->param_types[i] = INT4OID;
}
else
{
festate->param_types = NULL;
festate->param_values = NULL;
}
festate->extparams_done = false;
}
/*
* postgresIterateForeignScan
* Retrieve next row from the result set, or clear tuple slot to indicate
* EOF.
*/
static TupleTableSlot *
postgresIterateForeignScan(ForeignScanState *node)
{
PgFdwExecutionState *festate = (PgFdwExecutionState *) node->fdw_state;
TupleTableSlot *slot = node->ss.ss_ScanTupleSlot;
/*
* If this is the first call after Begin or ReScan, we need to create the
* cursor on the remote side.
*/
if (!festate->cursor_exists)
create_cursor(node);
/*
* Get some more tuples, if we've run out.
*/
if (festate->next_tuple >= festate->num_tuples)
{
/* No point in another fetch if we already detected EOF, though. */
if (!festate->eof_reached)
fetch_more_data(node);
/* If we didn't get any tuples, must be end of data. */
if (festate->next_tuple >= festate->num_tuples)
return ExecClearTuple(slot);
}
/*
* Return the next tuple.
*/
ExecStoreTuple(festate->tuples[festate->next_tuple++],
slot,
InvalidBuffer,
false);
return slot;
}
/*
* postgresReScanForeignScan
* Restart the scan.
*/
static void
postgresReScanForeignScan(ForeignScanState *node)
{
PgFdwExecutionState *festate = (PgFdwExecutionState *) node->fdw_state;
char sql[64];
PGresult *res;
/*
* Note: we assume that PARAM_EXTERN params don't change over the life of
* the query, so no need to reset extparams_done.
*/
/* If we haven't created the cursor yet, nothing to do. */
if (!festate->cursor_exists)
return;
/*
* If any internal parameters affecting this node have changed, we'd
* better destroy and recreate the cursor. Otherwise, rewinding it should
* be good enough. If we've only fetched zero or one batch, we needn't
* even rewind the cursor, just rescan what we have.
*/
if (node->ss.ps.chgParam != NULL)
{
festate->cursor_exists = false;
snprintf(sql, sizeof(sql), "CLOSE c%u",
festate->cursor_number);
}
else if (festate->fetch_ct_2 > 1)
{
snprintf(sql, sizeof(sql), "MOVE BACKWARD ALL IN c%u",
festate->cursor_number);
}
else
{
/* Easy: just rescan what we already have in memory, if anything */
festate->next_tuple = 0;
return;
}
/*
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
res = PQexec(festate->conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, sql);
PQclear(res);
/* Now force a fresh FETCH. */
festate->tuples = NULL;
festate->num_tuples = 0;
festate->next_tuple = 0;
festate->fetch_ct_2 = 0;
festate->eof_reached = false;
}
/*
* postgresEndForeignScan
* Finish scanning foreign table and dispose objects used for this scan
*/
static void
postgresEndForeignScan(ForeignScanState *node)
{
PgFdwExecutionState *festate = (PgFdwExecutionState *) node->fdw_state;
/* if festate is NULL, we are in EXPLAIN; nothing to do */
if (festate == NULL)
return;
/* Close the cursor if open, to prevent accumulation of cursors */
if (festate->cursor_exists)
close_cursor(festate->conn, festate->cursor_number);
/* Release remote connection */
ReleaseConnection(festate->conn);
festate->conn = NULL;
/* MemoryContexts will be deleted automatically. */
}
/*
* Estimate costs of executing given SQL statement.
*/
static void
get_remote_estimate(const char *sql, PGconn *conn,
double *rows, int *width,
Cost *startup_cost, Cost *total_cost)
{
PGresult *volatile res = NULL;
/* PGresult must be released before leaving this function. */
PG_TRY();
{
StringInfoData buf;
char *line;
char *p;
int n;
/*
* Execute EXPLAIN remotely on given SQL statement.
*/
initStringInfo(&buf);
appendStringInfo(&buf, "EXPLAIN %s", sql);
res = PQexec(conn, buf.data);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
pgfdw_report_error(ERROR, res, false, buf.data);
/*
* Extract cost numbers for topmost plan node. Note we search for a
* left paren from the end of the line to avoid being confused by
* other uses of parentheses.
*/
line = PQgetvalue(res, 0, 0);
p = strrchr(line, '(');
if (p == NULL)
elog(ERROR, "could not interpret EXPLAIN output: \"%s\"", line);
n = sscanf(p, "(cost=%lf..%lf rows=%lf width=%d)",
startup_cost, total_cost, rows, width);
if (n != 4)
elog(ERROR, "could not interpret EXPLAIN output: \"%s\"", line);
PQclear(res);
res = NULL;
}
PG_CATCH();
{
if (res)
PQclear(res);
PG_RE_THROW();
}
PG_END_TRY();
}
/*
* Create cursor for node's query with current parameter values.
*/
static void
create_cursor(ForeignScanState *node)
{
PgFdwExecutionState *festate = (PgFdwExecutionState *) node->fdw_state;
int numParams = festate->numParams;
Oid *types = festate->param_types;
const char **values = festate->param_values;
PGconn *conn = festate->conn;
char *sql;
StringInfoData buf;
PGresult *res;
/*
* Construct array of external parameter values in text format. Since
* there might be random unconvertible stuff in the ParamExternData array,
* take care to convert only values we actually need.
*
* Note that we leak the memory for the value strings until end of query;
* this doesn't seem like a big problem, and in any case we might need to
* recreate the cursor after a rescan, so we could need to re-use the
* values anyway.
*/
if (numParams > 0 && !festate->extparams_done)
{
ParamListInfo params = node->ss.ps.state->es_param_list_info;
int nestlevel;
List *param_numbers;
ListCell *lc;
nestlevel = set_transmission_modes();
param_numbers = (List *)
list_nth(festate->fdw_private, FdwPrivateExternParamIds);
foreach(lc, param_numbers)
{
int paramno = lfirst_int(lc);
ParamExternData *prm = ¶ms->params[paramno - 1];
/* give hook a chance in case parameter is dynamic */
if (!OidIsValid(prm->ptype) && params->paramFetch != NULL)
params->paramFetch(params, paramno);
/*
* Force the remote server to infer a type for this parameter.
* Since we explicitly cast every parameter (see deparse.c), the
* "inference" is trivial and will produce the desired result.
* This allows us to avoid assuming that the remote server has the
* same OIDs we do for the parameters' types.
*
* We'd not need to pass a type array to PQexecParams at all,
* except that there may be unused holes in the array, which
* will have to be filled with something or the remote server will
* complain. We arbitrarily set them to INT4OID earlier.
*/
types[paramno - 1] = InvalidOid;
/*
* Get string representation of each parameter value by invoking
* type-specific output function, unless the value is null.
*/
if (prm->isnull)
values[paramno - 1] = NULL;
else
{
Oid out_func;
bool isvarlena;
getTypeOutputInfo(prm->ptype, &out_func, &isvarlena);
values[paramno - 1] = OidOutputFunctionCall(out_func,
prm->value);
}
}
reset_transmission_modes(nestlevel);
festate->extparams_done = true;
}
/* Construct the DECLARE CURSOR command */
sql = strVal(list_nth(festate->fdw_private, FdwPrivateSelectSql));
initStringInfo(&buf);
appendStringInfo(&buf, "DECLARE c%u CURSOR FOR\n%s",
festate->cursor_number, sql);
/*
* We don't use a PG_TRY block here, so be careful not to throw error
* without releasing the PGresult.
*/
res = PQexecParams(conn, buf.data, numParams, types, values,
NULL, NULL, 0);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
pgfdw_report_error(ERROR, res, true, sql);
PQclear(res);
/* Mark the cursor as created, and show no tuples have been retrieved */
festate->cursor_exists = true;
festate->tuples = NULL;
festate->num_tuples = 0;
festate->next_tuple = 0;
festate->fetch_ct_2 = 0;
festate->eof_reached = false;
/* Clean up */
pfree(buf.data);
}
/*
* Fetch some more rows from the node's cursor.
*/
static void
fetch_more_data(ForeignScanState *node)
{
PgFdwExecutionState *festate = (PgFdwExecutionState *) node->fdw_state;
PGresult *volatile res = NULL;
MemoryContext oldcontext;