contrib/tsm_system_rows

contrib/tsm_system_rows/tsm_system_rows.c

@@ -0,0 +1,270 @@
+/*-------------------------------------------------------------------------
+ *
+ * tsm_system_rows.c
+ *	  interface routines for system_rows tablesample method
+ *
+ *
+ * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  contrib/tsm_system_rows_rowlimit/tsm_system_rows.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
+#include "postgres.h"
+
+#include "fmgr.h"
+
+#include "access/tablesample.h"
+#include "access/relscan.h"
+#include "miscadmin.h"
+#include "nodes/execnodes.h"
+#include "nodes/relation.h"
+#include "optimizer/clauses.h"
+#include "storage/bufmgr.h"
+#include "utils/sampling.h"
+
+PG_MODULE_MAGIC;
+
+/*
+ * State
+ */
+typedef struct
+{
+	SamplerRandomState randstate;
+	uint32			seed;			/* random seed */
+	BlockNumber		nblocks;		/* number of block in relation */
+	int32			ntuples;		/* number of tuples to return */
+	int32			donetuples;		/* tuples already returned */
+	OffsetNumber	lt;				/* last tuple returned from current block */
+	BlockNumber		step;			/* step size */
+	BlockNumber		lb;				/* last block visited */
+	BlockNumber		doneblocks;		/* number of already returned blocks */
+} SystemSamplerData;
+
+
+PG_FUNCTION_INFO_V1(tsm_system_rows_init);
+PG_FUNCTION_INFO_V1(tsm_system_rows_nextblock);
+PG_FUNCTION_INFO_V1(tsm_system_rows_nexttuple);
+PG_FUNCTION_INFO_V1(tsm_system_rows_examinetuple);
+PG_FUNCTION_INFO_V1(tsm_system_rows_end);
+PG_FUNCTION_INFO_V1(tsm_system_rows_reset);
+PG_FUNCTION_INFO_V1(tsm_system_rows_cost);
+
+static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
+
+/*
+ * Initializes the state.
+ */
+Datum
+tsm_system_rows_init(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc	   *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	uint32				seed = PG_GETARG_UINT32(1);
+	int32				ntuples = PG_ARGISNULL(2) ? -1 : PG_GETARG_INT32(2);
+	HeapScanDesc		scan = tsdesc->heapScan;
+	SystemSamplerData  *sampler;
+
+	if (ntuples < 1)
+		ereport(ERROR,
+				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+				 errmsg("invalid sample size"),
+				 errhint("Sample size must be positive integer value.")));
+
+	sampler = palloc0(sizeof(SystemSamplerData));
+
+	/* Remember initial values for reinit */
+	sampler->seed = seed;
+	sampler->nblocks = scan->rs_nblocks;
+	sampler->ntuples = ntuples;
+	sampler->donetuples = 0;
+	sampler->lt = InvalidOffsetNumber;
+	sampler->doneblocks = 0;
+
+	sampler_random_init_state(sampler->seed, sampler->randstate);
+
+	/* Find relative prime as step size for linear probing. */
+	sampler->step = random_relative_prime(sampler->nblocks, sampler->randstate);
+	/*
+	 * Randomize start position so that blocks close to step size don't have
+	 * higher probability of being chosen on very short scan.
+	 */
+	sampler->lb = sampler_random_fract(sampler->randstate) *
+		(sampler->nblocks / sampler->step);
+
+	tsdesc->tsmdata = (void *) sampler;
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Get next block number or InvalidBlockNumber when we're done.
+ *
+ * Uses linear probing algorithm for picking next block.
+ */
+Datum
+tsm_system_rows_nextblock(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc	   *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	SystemSamplerData  *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+
+	sampler->lb = (sampler->lb + sampler->step) % sampler->nblocks;
+	sampler->doneblocks++;
+
+	/* All blocks have been read, we're done */
+	if (sampler->doneblocks > sampler->nblocks ||
+		sampler->donetuples >= sampler->ntuples)
+		PG_RETURN_UINT32(InvalidBlockNumber);
+
+	PG_RETURN_UINT32(sampler->lb);
+}
+
+/*
+ * Get next tuple offset in current block or InvalidOffsetNumber if we are done
+ * with this block.
+ */
+Datum
+tsm_system_rows_nexttuple(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc	   *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	OffsetNumber		maxoffset = PG_GETARG_UINT16(2);
+	SystemSamplerData  *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+	OffsetNumber		tupoffset = sampler->lt;
+
+	if (tupoffset == InvalidOffsetNumber)
+		tupoffset = FirstOffsetNumber;
+	else
+		tupoffset++;
+
+	if (tupoffset > maxoffset ||
+		sampler->donetuples >= sampler->ntuples)
+		tupoffset = InvalidOffsetNumber;
+
+	sampler->lt = tupoffset;
+
+	PG_RETURN_UINT16(tupoffset);
+}
+
+/*
+ * Examine tuple and decide if it should be returned.
+ */
+Datum
+tsm_system_rows_examinetuple(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc	   *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	bool				visible = PG_GETARG_BOOL(3);
+	SystemSamplerData  *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+
+	if (!visible)
+		PG_RETURN_BOOL(false);
+
+	sampler->donetuples++;
+
+	PG_RETURN_BOOL(true);
+}
+
+/*
+ * Cleanup method.
+ */
+Datum
+tsm_system_rows_end(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+
+	pfree(tsdesc->tsmdata);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Reset state (called by ReScan).
+ */
+Datum
+tsm_system_rows_reset(PG_FUNCTION_ARGS)
+{
+	TableSampleDesc	   *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	SystemSamplerData  *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+
+	sampler->lt = InvalidOffsetNumber;
+	sampler->donetuples = 0;
+	sampler->doneblocks = 0;
+
+	sampler_random_init_state(sampler->seed, sampler->randstate);
+	sampler->step = random_relative_prime(sampler->nblocks, sampler->randstate);
+	sampler->lb = sampler_random_fract(sampler->randstate) * (sampler->nblocks / sampler->step);
+
+	PG_RETURN_VOID();
+}
+
+/*
+ * Costing function.
+ */
+Datum
+tsm_system_rows_cost(PG_FUNCTION_ARGS)
+{
+	PlannerInfo	   *root = (PlannerInfo *) PG_GETARG_POINTER(0);
+	Path		   *path = (Path *) PG_GETARG_POINTER(1);
+	RelOptInfo	   *baserel = (RelOptInfo *) PG_GETARG_POINTER(2);
+	List		   *args = (List *) PG_GETARG_POINTER(3);
+	BlockNumber	   *pages = (BlockNumber *) PG_GETARG_POINTER(4);
+	double		   *tuples = (double *) PG_GETARG_POINTER(5);
+	Node		   *limitnode;
+	int32			ntuples;
+
+	limitnode = linitial(args);
+	limitnode = estimate_expression_value(root, limitnode);
+
+	if (IsA(limitnode, RelabelType))
+		limitnode = (Node *) ((RelabelType *) limitnode)->arg;
+
+	if (IsA(limitnode, Const))
+		ntuples = DatumGetInt32(((Const *) limitnode)->constvalue);
+	else
+	{
+		/* Default ntuples if the estimation didn't return Const. */
+		ntuples = 1000;
+	}
+
+	*pages = Min(baserel->pages, ntuples);
+	*tuples = ntuples;
+	path->rows = *tuples;
+
+	PG_RETURN_VOID();
+}
+
+
+static uint32
+gcd (uint32 a, uint32 b)
+{
+	uint32 c;
+
+	while (a != 0)
+	{
+		c = a;
+		a = b % a;
+		b = c;
+	}
+
+	return b;
+}
+
+static uint32
+random_relative_prime(uint32 n, SamplerRandomState randstate)
+{
+	/* Pick random starting number, with some limits on what it can be. */
+	uint32 r = (uint32) sampler_random_fract(randstate) * n/2 + n/4,
+		   t;
+
+	/*
+	 * This should only take 2 or 3 iterations as the probability of 2 numbers
+	 * being relatively prime is ~61%.
+	 */
+	while ((t = gcd(r, n)) > 1)
+	{
+		CHECK_FOR_INTERRUPTS();
+		r /= t;
+	}
+
+	return r;
+}