--- /dev/null
+/*-------------------------------------------------------------------------
+ *
+ * tsm_system_time.c
+ * interface routines for system_time tablesample method
+ *
+ *
+ * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ * contrib/tsm_system_time_rowlimit/tsm_system_time.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"
+#include "utils/spccache.h"
+#include "utils/timestamp.h"
+
+PG_MODULE_MAGIC;
+
+/*
+ * State
+ */
+typedef struct
+{
+ SamplerRandomState randstate;
+ uint32 seed; /* random seed */
+ BlockNumber nblocks; /* number of block in relation */
+ int32 time; /* time limit for sampling */
+ TimestampTz start_time; /* start time of sampling */
+ TimestampTz end_time; /* end time of sampling */
+ OffsetNumber lt; /* last tuple returned from current block */
+ BlockNumber step; /* step size */
+ BlockNumber lb; /* last block visited */
+ BlockNumber estblocks; /* estimated number of returned blocks (moving) */
+ BlockNumber doneblocks; /* number of already returned blocks */
+} SystemSamplerData;
+
+
+PG_FUNCTION_INFO_V1(tsm_system_time_init);
+PG_FUNCTION_INFO_V1(tsm_system_time_nextblock);
+PG_FUNCTION_INFO_V1(tsm_system_time_nexttuple);
+PG_FUNCTION_INFO_V1(tsm_system_time_end);
+PG_FUNCTION_INFO_V1(tsm_system_time_reset);
+PG_FUNCTION_INFO_V1(tsm_system_time_cost);
+
+static uint32 random_relative_prime(uint32 n, SamplerRandomState randstate);
+
+/*
+ * Initializes the state.
+ */
+Datum
+tsm_system_time_init(PG_FUNCTION_ARGS)
+{
+ TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+ uint32 seed = PG_GETARG_UINT32(1);
+ int32 time = PG_ARGISNULL(2) ? -1 : PG_GETARG_INT32(2);
+ HeapScanDesc scan = tsdesc->heapScan;
+ SystemSamplerData *sampler;
+
+ if (time < 1)
+ ereport(ERROR,
+ (errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+ errmsg("invalid time limit"),
+ errhint("Time limit must be positive integer value.")));
+
+ sampler = palloc0(sizeof(SystemSamplerData));
+
+ /* Remember initial values for reinit */
+ sampler->seed = seed;
+ sampler->nblocks = scan->rs_nblocks;
+ sampler->lt = InvalidOffsetNumber;
+ sampler->estblocks = 2;
+ sampler->doneblocks = 0;
+ sampler->time = time;
+ sampler->start_time = GetCurrentTimestamp();
+ sampler->end_time = TimestampTzPlusMilliseconds(sampler->start_time,
+ sampler->time);
+
+ 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_time_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)
+ PG_RETURN_UINT32(InvalidBlockNumber);
+
+ /*
+ * Update the estimations for time limit at least 10 times per estimated
+ * number of returned blocks to handle variations in block read speed.
+ */
+ if (sampler->doneblocks % Max(sampler->estblocks/10, 1) == 0)
+ {
+ TimestampTz now = GetCurrentTimestamp();
+ long secs;
+ int usecs;
+ int usecs_remaining;
+ int time_per_block;
+
+ TimestampDifference(sampler->start_time, now, &secs, &usecs);
+ usecs += (int) secs * 1000000;
+
+ time_per_block = usecs / sampler->doneblocks;
+
+ /* No time left, end. */
+ TimestampDifference(now, sampler->end_time, &secs, &usecs);
+ if (secs <= 0 && usecs <= 0)
+ PG_RETURN_UINT32(InvalidBlockNumber);
+
+ /* Remaining microseconds */
+ usecs_remaining = usecs + (int) secs * 1000000;
+
+ /* Recalculate estimated returned number of blocks */
+ if (time_per_block < usecs_remaining && time_per_block > 0)
+ sampler->estblocks = sampler->time * time_per_block;
+ }
+
+ PG_RETURN_UINT32(sampler->lb);
+}
+
+/*
+ * Get next tuple offset in current block or InvalidOffsetNumber if we are done
+ * with this block.
+ */
+Datum
+tsm_system_time_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)
+ tupoffset = InvalidOffsetNumber;
+
+ sampler->lt = tupoffset;
+
+ PG_RETURN_UINT16(tupoffset);
+}
+
+/*
+ * Cleanup method.
+ */
+Datum
+tsm_system_time_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_time_reset(PG_FUNCTION_ARGS)
+{
+ TableSampleDesc *tsdesc = (TableSampleDesc *) PG_GETARG_POINTER(0);
+ SystemSamplerData *sampler = (SystemSamplerData *) tsdesc->tsmdata;
+
+ sampler->lt = InvalidOffsetNumber;
+ sampler->start_time = GetCurrentTimestamp();
+ sampler->end_time = TimestampTzPlusMilliseconds(sampler->start_time,
+ sampler->time);
+ sampler->estblocks = 2;
+ 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_time_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 time;
+ BlockNumber relpages;
+ double reltuples;
+ double density;
+ double spc_random_page_cost;
+
+ limitnode = linitial(args);
+ limitnode = estimate_expression_value(root, limitnode);
+
+ if (IsA(limitnode, RelabelType))
+ limitnode = (Node *) ((RelabelType *) limitnode)->arg;
+
+ if (IsA(limitnode, Const))
+ time = DatumGetInt32(((Const *) limitnode)->constvalue);
+ else
+ {
+ /* Default time (1s) if the estimation didn't return Const. */
+ time = 1000;
+ }
+
+ relpages = baserel->pages;
+ reltuples = baserel->tuples;
+
+ /* estimate the tuple density */
+ if (relpages > 0)
+ density = reltuples / (double) relpages;
+ else
+ density = (BLCKSZ - SizeOfPageHeaderData) / baserel->width;
+
+ /*
+ * We equal random page cost value to number of ms it takes to read the
+ * random page here which is far from accurate but we don't have anything
+ * better to base our predicted page reads.
+ */
+ get_tablespace_page_costs(baserel->reltablespace,
+ &spc_random_page_cost,
+ NULL);
+
+ /*
+ * Assumption here is that we'll never read less then 1% of table pages,
+ * this is here mainly because it is much less bad to overestimate than
+ * underestimate and using just spc_random_page_cost will probably lead
+ * to underestimations in general.
+ */
+ *pages = Min(baserel->pages, Max(time/spc_random_page_cost, baserel->pages/100));
+ *tuples = rint(density * (double) *pages * path->rows / baserel->tuples);
+ 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;
+}
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