1 files changed, 284 insertions, 161 deletions

diff --git a/contrib/tsm_system_rows/tsm_system_rows.c b/contrib/tsm_system_rows/tsm_system_rows.c
index e325eaff498..f251e3e5e06 100644
--- a/contrib/tsm_system_rows/tsm_system_rows.c
+++ b/contrib/tsm_system_rows/tsm_system_rows.c
@@ -1,240 +1,356 @@
 /*-------------------------------------------------------------------------
  *
  * tsm_system_rows.c
- *	  interface routines for system_rows tablesample method
+ *	  support routines for SYSTEM_ROWS tablesample method
  *
+ * The desire here is to produce a random sample with a given number of rows
+ * (or the whole relation, if that is fewer rows).  We use a block-sampling
+ * approach.  To ensure that the whole relation will be visited if necessary,
+ * we start at a randomly chosen block and then advance with a stride that
+ * is randomly chosen but is relatively prime to the relation's nblocks.
  *
- * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
+ * Because of the dependence on nblocks, this method cannot be repeatable
+ * across queries.  (Even if the user hasn't explicitly changed the relation,
+ * maintenance activities such as autovacuum might change nblocks.)  However,
+ * we can at least make it repeatable across scans, by determining the
+ * sampling pattern only once on the first scan.  This means that rescans
+ * won't visit blocks added after the first scan, but that is fine since
+ * such blocks shouldn't contain any visible tuples anyway.
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  contrib/tsm_system_rows_rowlimit/tsm_system_rows.c
+ *	  contrib/tsm_system_rows/tsm_system_rows.c
  *
  *-------------------------------------------------------------------------
  */
 
 #include "postgres.h"
 
-#include "fmgr.h"
-
-#include "access/tablesample.h"
 #include "access/relscan.h"
+#include "access/tsmapi.h"
+#include "catalog/pg_type.h"
 #include "miscadmin.h"
-#include "nodes/execnodes.h"
-#include "nodes/relation.h"
 #include "optimizer/clauses.h"
-#include "storage/bufmgr.h"
+#include "optimizer/cost.h"
 #include "utils/sampling.h"
 
 PG_MODULE_MAGIC;
 
-/*
- * State
- */
+PG_FUNCTION_INFO_V1(tsm_system_rows_handler);
+
+
+/* Private 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 */
+	int64		ntuples;		/* number of tuples to return */
+	int64		donetuples;		/* number of tuples already returned */
 	OffsetNumber lt;			/* last tuple returned from current block */
-	BlockNumber step;			/* step size */
+	BlockNumber doneblocks;		/* number of already-scanned blocks */
 	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);
-
+	/* these three values are not changed during a rescan: */
+	BlockNumber nblocks;		/* number of blocks in relation */
+	BlockNumber firstblock;		/* first block to sample from */
+	BlockNumber step;			/* step size, or 0 if not set yet */
+} SystemRowsSamplerData;
+
+static void system_rows_samplescangetsamplesize(PlannerInfo *root,
+									RelOptInfo *baserel,
+									List *paramexprs,
+									BlockNumber *pages,
+									double *tuples);
+static void system_rows_initsamplescan(SampleScanState *node,
+						   int eflags);
+static void system_rows_beginsamplescan(SampleScanState *node,
+							Datum *params,
+							int nparams,
+							uint32 seed);
+static BlockNumber system_rows_nextsampleblock(SampleScanState *node);
+static OffsetNumber system_rows_nextsampletuple(SampleScanState *node,
+							BlockNumber blockno,
+							OffsetNumber maxoffset);
+static bool SampleOffsetVisible(OffsetNumber tupoffset, HeapScanDesc scan);
 static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
 
+
 /*
- * Initializes the state.
+ * Create a TsmRoutine descriptor for the SYSTEM_ROWS method.
  */
 Datum
-tsm_system_rows_init(PG_FUNCTION_ARGS)
+tsm_system_rows_handler(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;
+	TsmRoutine *tsm = makeNode(TsmRoutine);
 
-	if (ntuples < 1)
-		ereport(ERROR,
-				(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
-				 errmsg("invalid sample size"),
-				 errhint("Sample size must be positive integer value.")));
+	tsm->parameterTypes = list_make1_oid(INT8OID);
 
-	sampler = palloc0(sizeof(SystemSamplerData));
+	/* See notes at head of file */
+	tsm->repeatable_across_queries = false;
+	tsm->repeatable_across_scans = true;
 
-	/* 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);
+	tsm->SampleScanGetSampleSize = system_rows_samplescangetsamplesize;
+	tsm->InitSampleScan = system_rows_initsamplescan;
+	tsm->BeginSampleScan = system_rows_beginsamplescan;
+	tsm->NextSampleBlock = system_rows_nextsampleblock;
+	tsm->NextSampleTuple = system_rows_nextsampletuple;
+	tsm->EndSampleScan = NULL;
 
-	tsdesc->tsmdata = (void *) sampler;
-
-	PG_RETURN_VOID();
+	PG_RETURN_POINTER(tsm);
 }
 
 /*
- * Get next block number or InvalidBlockNumber when we're done.
- *
- * Uses linear probing algorithm for picking next block.
+ * Sample size estimation.
  */
-Datum
-tsm_system_rows_nextblock(PG_FUNCTION_ARGS)
+static void
+system_rows_samplescangetsamplesize(PlannerInfo *root,
+									RelOptInfo *baserel,
+									List *paramexprs,
+									BlockNumber *pages,
+									double *tuples)
 {
-	TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
-	SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+	Node	   *limitnode;
+	int64		ntuples;
+	double		npages;
 
-	sampler->lb = (sampler->lb + sampler->step) % sampler->nblocks;
-	sampler->doneblocks++;
+	/* Try to extract an estimate for the limit rowcount */
+	limitnode = (Node *) linitial(paramexprs);
+	limitnode = estimate_expression_value(root, limitnode);
 
-	/* All blocks have been read, we're done */
-	if (sampler->doneblocks > sampler->nblocks ||
-		sampler->donetuples >= sampler->ntuples)
-		PG_RETURN_UINT32(InvalidBlockNumber);
+	if (IsA(limitnode, Const) &&
+		!((Const *) limitnode)->constisnull)
+	{
+		ntuples = DatumGetInt64(((Const *) limitnode)->constvalue);
+		if (ntuples < 0)
+		{
+			/* Default ntuples if the value is bogus */
+			ntuples = 1000;
+		}
+	}
+	else
+	{
+		/* Default ntuples if we didn't obtain a non-null Const */
+		ntuples = 1000;
+	}
 
-	PG_RETURN_UINT32(sampler->lb);
-}
+	/* Clamp to the estimated relation size */
+	if (ntuples > baserel->tuples)
+		ntuples = (int64) baserel->tuples;
+	ntuples = clamp_row_est(ntuples);
 
-/*
- * 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 (baserel->tuples > 0 && baserel->pages > 0)
+	{
+		/* Estimate number of pages visited based on tuple density */
+		double		density = baserel->tuples / (double) baserel->pages;
 
-	if (tupoffset == InvalidOffsetNumber)
-		tupoffset = FirstOffsetNumber;
+		npages = ntuples / density;
+	}
 	else
-		tupoffset++;
-
-	if (tupoffset > maxoffset ||
-		sampler->donetuples >= sampler->ntuples)
-		tupoffset = InvalidOffsetNumber;
+	{
+		/* For lack of data, assume one tuple per page */
+		npages = ntuples;
+	}
 
-	sampler->lt = tupoffset;
+	/* Clamp to sane value */
+	npages = clamp_row_est(Min((double) baserel->pages, npages));
 
-	PG_RETURN_UINT16(tupoffset);
+	*pages = npages;
+	*tuples = ntuples;
 }
 
 /*
- * Examine tuple and decide if it should be returned.
+ * Initialize during executor setup.
  */
-Datum
-tsm_system_rows_examinetuple(PG_FUNCTION_ARGS)
+static void
+system_rows_initsamplescan(SampleScanState *node, int eflags)
 {
-	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);
+	node->tsm_state = palloc0(sizeof(SystemRowsSamplerData));
+	/* Note the above leaves tsm_state->step equal to zero */
 }
 
 /*
- * Cleanup method.
+ * Examine parameters and prepare for a sample scan.
  */
-Datum
-tsm_system_rows_end(PG_FUNCTION_ARGS)
+static void
+system_rows_beginsamplescan(SampleScanState *node,
+							Datum *params,
+							int nparams,
+							uint32 seed)
 {
-	TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+	SystemRowsSamplerData *sampler = (SystemRowsSamplerData *) node->tsm_state;
+	int64		ntuples = DatumGetInt64(params[0]);
+
+	if (ntuples < 0)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TABLESAMPLE_ARGUMENT),
+				 errmsg("sample size must not be negative")));
 
-	pfree(tsdesc->tsmdata);
+	sampler->seed = seed;
+	sampler->ntuples = ntuples;
+	sampler->donetuples = 0;
+	sampler->lt = InvalidOffsetNumber;
+	sampler->doneblocks = 0;
+	/* lb will be initialized during first NextSampleBlock call */
+	/* we intentionally do not change nblocks/firstblock/step here */
 
-	PG_RETURN_VOID();
+	/*
+	 * We *must* use pagemode visibility checking in this module, so force
+	 * that even though it's currently default.
+	 */
+	node->use_pagemode = true;
 }
 
 /*
- * Reset state (called by ReScan).
+ * Select next block to sample.
+ *
+ * Uses linear probing algorithm for picking next block.
  */
-Datum
-tsm_system_rows_reset(PG_FUNCTION_ARGS)
+static BlockNumber
+system_rows_nextsampleblock(SampleScanState *node)
 {
-	TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
-	SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+	SystemRowsSamplerData *sampler = (SystemRowsSamplerData *) node->tsm_state;
+	HeapScanDesc scan = node->ss.ss_currentScanDesc;
 
-	sampler->lt = InvalidOffsetNumber;
-	sampler->donetuples = 0;
-	sampler->doneblocks = 0;
+	/* First call within scan? */
+	if (sampler->doneblocks == 0)
+	{
+		/* First scan within query? */
+		if (sampler->step == 0)
+		{
+			/* Initialize now that we have scan descriptor */
+			SamplerRandomState randstate;
+
+			/* If relation is empty, there's nothing to scan */
+			if (scan->rs_nblocks == 0)
+				return InvalidBlockNumber;
+
+			/* We only need an RNG during this setup step */
+			sampler_random_init_state(sampler->seed, randstate);
+
+			/* Compute nblocks/firstblock/step only once per query */
+			sampler->nblocks = scan->rs_nblocks;
 
-	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);
+			/* Choose random starting block within the relation */
+			/* (Actually this is the predecessor of the first block visited) */
+			sampler->firstblock = sampler_random_fract(randstate) *
+				sampler->nblocks;
+
+			/* Find relative prime as step size for linear probing */
+			sampler->step = random_relative_prime(sampler->nblocks, randstate);
+		}
+
+		/* Reinitialize lb */
+		sampler->lb = sampler->firstblock;
+	}
+
+	/* If we've read all blocks or returned all needed tuples, we're done */
+	if (++sampler->doneblocks > sampler->nblocks ||
+		sampler->donetuples >= sampler->ntuples)
+		return InvalidBlockNumber;
+
+	/*
+	 * It's probably impossible for scan->rs_nblocks to decrease between scans
+	 * within a query; but just in case, loop until we select a block number
+	 * less than scan->rs_nblocks.  We don't care if scan->rs_nblocks has
+	 * increased since the first scan.
+	 */
+	do
+	{
+		/* Advance lb, using uint64 arithmetic to forestall overflow */
+		sampler->lb = ((uint64) sampler->lb + sampler->step) % sampler->nblocks;
+	} while (sampler->lb >= scan->rs_nblocks);
 
-	PG_RETURN_VOID();
+	return sampler->lb;
 }
 
 /*
- * Costing function.
+ * Select next sampled tuple in current block.
+ *
+ * In block sampling, we just want to sample all the tuples in each selected
+ * block.
+ *
+ * When we reach end of the block, return InvalidOffsetNumber which tells
+ * SampleScan to go to next block.
  */
-Datum
-tsm_system_rows_cost(PG_FUNCTION_ARGS)
+static OffsetNumber
+system_rows_nextsampletuple(SampleScanState *node,
+							BlockNumber blockno,
+							OffsetNumber maxoffset)
 {
-	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;
+	SystemRowsSamplerData *sampler = (SystemRowsSamplerData *) node->tsm_state;
+	HeapScanDesc scan = node->ss.ss_currentScanDesc;
+	OffsetNumber tupoffset = sampler->lt;
 
-	limitnode = linitial(args);
-	limitnode = estimate_expression_value(root, limitnode);
+	/* Quit if we've returned all needed tuples */
+	if (sampler->donetuples >= sampler->ntuples)
+		return InvalidOffsetNumber;
 
-	if (IsA(limitnode, RelabelType))
-		limitnode = (Node *) ((RelabelType *) limitnode)->arg;
+	/*
+	 * Because we should only count visible tuples as being returned, we need
+	 * to search for a visible tuple rather than just let the core code do it.
+	 */
 
-	if (IsA(limitnode, Const))
-		ntuples = DatumGetInt32(((Const *) limitnode)->constvalue);
-	else
+	/* We rely on the data accumulated in pagemode access */
+	Assert(scan->rs_pageatatime);
+	for (;;)
 	{
-		/* Default ntuples if the estimation didn't return Const. */
-		ntuples = 1000;
+		/* Advance to next possible offset on page */
+		if (tupoffset == InvalidOffsetNumber)
+			tupoffset = FirstOffsetNumber;
+		else
+			tupoffset++;
+
+		/* Done? */
+		if (tupoffset > maxoffset)
+		{
+			tupoffset = InvalidOffsetNumber;
+			break;
+		}
+
+		/* Found a candidate? */
+		if (SampleOffsetVisible(tupoffset, scan))
+		{
+			sampler->donetuples++;
+			break;
+		}
 	}
 
-	*pages = Min(baserel->pages, ntuples);
-	*tuples = ntuples;
-	path->rows = *tuples;
+	sampler->lt = tupoffset;
 
-	PG_RETURN_VOID();
+	return tupoffset;
 }
 
+/*
+ * Check if tuple offset is visible
+ *
+ * In pageatatime mode, heapgetpage() already did visibility checks,
+ * so just look at the info it left in rs_vistuples[].
+ */
+static bool
+SampleOffsetVisible(OffsetNumber tupoffset, HeapScanDesc scan)
+{
+	int			start = 0,
+				end = scan->rs_ntuples - 1;
+
+	while (start <= end)
+	{
+		int			mid = (start + end) / 2;
+		OffsetNumber curoffset = scan->rs_vistuples[mid];
+
+		if (tupoffset == curoffset)
+			return true;
+		else if (tupoffset < curoffset)
+			end = mid - 1;
+		else
+			start = mid + 1;
+	}
+
+	return false;
+}
 
+/*
+ * Compute greatest common divisor of two uint32's.
+ */
 static uint32
 gcd(uint32 a, uint32 b)
 {
@@ -250,22 +366,29 @@ gcd(uint32 a, uint32 b)
 	return b;
 }
 
+/*
+ * Pick a random value less than and relatively prime to n, if possible
+ * (else return 1).
+ */
 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;
+	uint32		r;
+
+	/* Safety check to avoid infinite loop or zero result for small n. */
+	if (n <= 1)
+		return 1;
 
 	/*
 	 * This should only take 2 or 3 iterations as the probability of 2 numbers
-	 * being relatively prime is ~61%.
+	 * being relatively prime is ~61%; but just in case, we'll include a
+	 * CHECK_FOR_INTERRUPTS in the loop.
 	 */
-	while ((t = gcd(r, n)) > 1)
+	do
 	{
 		CHECK_FOR_INTERRUPTS();
-		r /= t;
-	}
+		r = (uint32) (sampler_random_fract(randstate) * n);
+	} while (r == 0 || gcd(r, n) > 1);
 
 	return r;
 }