#include "postgres.h"
#include "access/hash.h"
+#include "lib/hyperloglog.h"
#include "libpq/pqformat.h"
+#include "port/pg_bswap.h"
#include "utils/builtins.h"
+#include "utils/guc.h"
#include "utils/inet.h"
+#include "utils/sortsupport.h"
/*
#define lobits(addr) \
((unsigned long)(((addr)->d<<16)|((addr)->e<<8)|((addr)->f)))
+/* sortsupport for macaddr */
+typedef struct
+{
+ int64 input_count; /* number of non-null values seen */
+ bool estimating; /* true if estimating cardinality */
+
+ hyperLogLogState abbr_card; /* cardinality estimator */
+} macaddr_sortsupport_state;
+
+static int macaddr_cmp_internal(macaddr *a1, macaddr *a2);
+static int macaddr_fast_cmp(Datum x, Datum y, SortSupport ssup);
+static int macaddr_cmp_abbrev(Datum x, Datum y, SortSupport ssup);
+static bool macaddr_abbrev_abort(int memtupcount, SortSupport ssup);
+static Datum macaddr_abbrev_convert(Datum original, SortSupport ssup);
+
/*
* MAC address reader. Accepts several common notations.
*/
* Comparison function for sorting:
*/
-static int32
+static int
macaddr_cmp_internal(macaddr *a1, macaddr *a2)
{
if (hibits(a1) < hibits(a2))
PG_RETURN_MACADDR_P(result);
}
+
+/*
+ * SortSupport strategy function. Populates a SortSupport struct with the
+ * information necessary to use comparison by abbreviated keys.
+ */
+Datum
+macaddr_sortsupport(PG_FUNCTION_ARGS)
+{
+ SortSupport ssup = (SortSupport) PG_GETARG_POINTER(0);
+
+ ssup->comparator = macaddr_fast_cmp;
+ ssup->ssup_extra = NULL;
+
+ if (ssup->abbreviate)
+ {
+ macaddr_sortsupport_state *uss;
+ MemoryContext oldcontext;
+
+ oldcontext = MemoryContextSwitchTo(ssup->ssup_cxt);
+
+ uss = palloc(sizeof(macaddr_sortsupport_state));
+ uss->input_count = 0;
+ uss->estimating = true;
+ initHyperLogLog(&uss->abbr_card, 10);
+
+ ssup->ssup_extra = uss;
+
+ ssup->comparator = macaddr_cmp_abbrev;
+ ssup->abbrev_converter = macaddr_abbrev_convert;
+ ssup->abbrev_abort = macaddr_abbrev_abort;
+ ssup->abbrev_full_comparator = macaddr_fast_cmp;
+
+ MemoryContextSwitchTo(oldcontext);
+ }
+
+ PG_RETURN_VOID();
+}
+
+/*
+ * SortSupport "traditional" comparison function. Pulls two MAC addresses from
+ * the heap and runs a standard comparison on them.
+ */
+static int
+macaddr_fast_cmp(Datum x, Datum y, SortSupport ssup)
+{
+ macaddr *arg1 = DatumGetMacaddrP(x);
+ macaddr *arg2 = DatumGetMacaddrP(y);
+
+ return macaddr_cmp_internal(arg1, arg2);
+}
+
+/*
+ * SortSupport abbreviated key comparison function. Compares two MAC addresses
+ * quickly by treating them like integers, and without having to go the heap.
+ */
+static int
+macaddr_cmp_abbrev(Datum x, Datum y, SortSupport ssup)
+{
+ if (x > y)
+ return 1;
+ else if (x == y)
+ return 0;
+ else
+ return -1;
+}
+
+/*
+ * Callback for estimating effectiveness of abbreviated key optimization.
+ *
+ * We pay no attention to the cardinality of the non-abbreviated data, because
+ * there is no equality fast-path within authoritative macaddr comparator.
+ */
+static bool
+macaddr_abbrev_abort(int memtupcount, SortSupport ssup)
+{
+ macaddr_sortsupport_state *uss = ssup->ssup_extra;
+ double abbr_card;
+
+ if (memtupcount < 10000 || uss->input_count < 10000 || !uss->estimating)
+ return false;
+
+ abbr_card = estimateHyperLogLog(&uss->abbr_card);
+
+ /*
+ * If we have >100k distinct values, then even if we were sorting many
+ * billion rows we'd likely still break even, and the penalty of undoing
+ * that many rows of abbrevs would probably not be worth it. At this point
+ * we stop counting because we know that we're now fully committed.
+ */
+ if (abbr_card > 100000.0)
+ {
+#ifdef TRACE_SORT
+ if (trace_sort)
+ elog(LOG,
+ "macaddr_abbrev: estimation ends at cardinality %f"
+ " after " INT64_FORMAT " values (%d rows)",
+ abbr_card, uss->input_count, memtupcount);
+#endif
+ uss->estimating = false;
+ return false;
+ }
+
+ /*
+ * Target minimum cardinality is 1 per ~2k of non-null inputs. 0.5 row
+ * fudge factor allows us to abort earlier on genuinely pathological data
+ * where we've had exactly one abbreviated value in the first 2k
+ * (non-null) rows.
+ */
+ if (abbr_card < uss->input_count / 2000.0 + 0.5)
+ {
+#ifdef TRACE_SORT
+ if (trace_sort)
+ elog(LOG,
+ "macaddr_abbrev: aborting abbreviation at cardinality %f"
+ " below threshold %f after " INT64_FORMAT " values (%d rows)",
+ abbr_card, uss->input_count / 2000.0 + 0.5, uss->input_count,
+ memtupcount);
+#endif
+ return true;
+ }
+
+#ifdef TRACE_SORT
+ if (trace_sort)
+ elog(LOG,
+ "macaddr_abbrev: cardinality %f after " INT64_FORMAT
+ " values (%d rows)", abbr_card, uss->input_count, memtupcount);
+#endif
+
+ return false;
+}
+
+/*
+ * SortSupport converstion routine. Converts original macaddr representation
+ * to abbreviated key representation.
+ *
+ * Packs the bytes of a 6-byte MAC address into a Datum and treats it as an
+ * unsigned integer for purposes of comparison. On a 64-bit machine, there
+ * will be two zeroed bytes of padding. The integer is converted to native
+ * endianness to facilitate easy comparison.
+ */
+static Datum
+macaddr_abbrev_convert(Datum original, SortSupport ssup)
+{
+ macaddr_sortsupport_state *uss = ssup->ssup_extra;
+ macaddr *authoritative = DatumGetMacaddrP(original);
+ Datum res;
+
+ /*
+ * On a 64-bit machine, zero out the 8-byte datum and copy the 6 bytes of
+ * the MAC address in. There will be two bytes of zero padding on the end
+ * of the least significant bits.
+ */
+#if SIZEOF_DATUM == 8
+ memset(&res, 0, SIZEOF_DATUM);
+ memcpy(&res, authoritative, sizeof(macaddr));
+#else /* SIZEOF_DATUM != 8 */
+ memcpy(&res, authoritative, SIZEOF_DATUM);
+#endif
+ uss->input_count += 1;
+
+ /*
+ * Cardinality estimation. The estimate uses uint32, so on a 64-bit
+ * architecture, XOR the two 32-bit halves together to produce slightly
+ * more entropy. The two zeroed bytes won't have any practical impact on
+ * this operation.
+ */
+ if (uss->estimating)
+ {
+ uint32 tmp;
+
+#if SIZEOF_DATUM == 8
+ tmp = (uint32) res ^ (uint32) ((uint64) res >> 32);
+#else /* SIZEOF_DATUM != 8 */
+ tmp = (uint32) res;
+#endif
+
+ addHyperLogLog(&uss->abbr_card, DatumGetUInt32(hash_uint32(tmp)));
+ }
+
+ /*
+ * Byteswap on little-endian machines.
+ *
+ * This is needed so that macaddr_cmp_abbrev() (an unsigned integer 3-way
+ * comparator) works correctly on all platforms. Without this, the
+ * comparator would have to call memcmp() with a pair of pointers to the
+ * first byte of each abbreviated key, which is slower.
+ */
+ res = DatumBigEndianToNative(res);
+
+ return res;
+}
projects / postgresql / commitdiff