From a76ef15d9fc9207a0758e8d6f6700dc8c931a934 Mon Sep 17 00:00:00 2001
From: Robert Haas <rhaas@postgresql.org>
Date: Fri, 6 Nov 2015 12:10:42 -0500
Subject: [PATCH] Add sort support routine for the UUID data type.
This introduces a simple encoding scheme to produce abbreviated keys:
pack as many bytes of each UUID as will fit into a Datum. On
little-endian machines, a byteswap is also performed; the abbreviated
comparator can therefore just consist of a simple 3-way unsigned integer
comparison.
The purpose of this change is to speed up sorting data on a column
of type UUID.
Peter Geoghegan
---
src/backend/utils/adt/uuid.c | 187 ++++++++++++++++++++++++++++++++
src/include/catalog/pg_amproc.h | 1 +
src/include/catalog/pg_proc.h | 2 +
src/include/utils/builtins.h | 1 +
4 files changed, 191 insertions(+)
diff --git a/src/backend/utils/adt/uuid.c b/src/backend/utils/adt/uuid.c
index bb76b8df668..6356229e8eb 100644
--- a/src/backend/utils/adt/uuid.c
+++ b/src/backend/utils/adt/uuid.c
@@ -14,8 +14,12 @@
#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/sortsupport.h"
#include "utils/uuid.h"
/* uuid size in bytes */
@@ -27,8 +31,21 @@ struct pg_uuid_t
unsigned char data[UUID_LEN];
};
+/* sortsupport for uuid */
+typedef struct
+{
+ int64 input_count; /* number of non-null values seen */
+ bool estimating; /* true if estimating cardinality */
+
+ hyperLogLogState abbr_card; /* cardinality estimator */
+} uuid_sortsupport_state;
+
static void string_to_uuid(const char *source, pg_uuid_t *uuid);
static int uuid_internal_cmp(const pg_uuid_t *arg1, const pg_uuid_t *arg2);
+static int uuid_fast_cmp(Datum x, Datum y, SortSupport ssup);
+static int uuid_cmp_abbrev(Datum x, Datum y, SortSupport ssup);
+static bool uuid_abbrev_abort(int memtupcount, SortSupport ssup);
+static Datum uuid_abbrev_convert(Datum original, SortSupport ssup);
Datum
uuid_in(PG_FUNCTION_ARGS)
@@ -222,6 +239,176 @@ uuid_cmp(PG_FUNCTION_ARGS)
PG_RETURN_INT32(uuid_internal_cmp(arg1, arg2));
}
+/*
+ * Sort support strategy routine
+ */
+Datum
+uuid_sortsupport(PG_FUNCTION_ARGS)
+{
+ SortSupport ssup = (SortSupport) PG_GETARG_POINTER(0);
+
+ ssup->comparator = uuid_fast_cmp;
+ ssup->ssup_extra = NULL;
+
+ if (ssup->abbreviate)
+ {
+ uuid_sortsupport_state *uss;
+ MemoryContext oldcontext;
+
+ oldcontext = MemoryContextSwitchTo(ssup->ssup_cxt);
+
+ uss = palloc(sizeof(uuid_sortsupport_state));
+ uss->input_count = 0;
+ uss->estimating = true;
+ initHyperLogLog(&uss->abbr_card, 10);
+
+ ssup->ssup_extra = uss;
+
+ ssup->comparator = uuid_cmp_abbrev;
+ ssup->abbrev_converter = uuid_abbrev_convert;
+ ssup->abbrev_abort = uuid_abbrev_abort;
+ ssup->abbrev_full_comparator = uuid_fast_cmp;
+
+ MemoryContextSwitchTo(oldcontext);
+ }
+
+ PG_RETURN_VOID();
+}
+
+/*
+ * SortSupport comparison func
+ */
+static int
+uuid_fast_cmp(Datum x, Datum y, SortSupport ssup)
+{
+ pg_uuid_t *arg1 = DatumGetUUIDP(x);
+ pg_uuid_t *arg2 = DatumGetUUIDP(y);
+
+ return uuid_internal_cmp(arg1, arg2);
+}
+
+/*
+ * Abbreviated key comparison func
+ */
+static int
+uuid_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 uuid comparator.
+ */
+static bool
+uuid_abbrev_abort(int memtupcount, SortSupport ssup)
+{
+ uuid_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. Stop even
+ * counting at that point.
+ */
+ if (abbr_card > 100000.0)
+ {
+#ifdef TRACE_SORT
+ if (trace_sort)
+ elog(LOG,
+ "uuid_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,
+ "uuid_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,
+ "uuid_abbrev: cardinality %f after " INT64_FORMAT
+ " values (%d rows)", abbr_card, uss->input_count, memtupcount);
+#endif
+
+ return false;
+}
+
+/*
+ * Conversion routine for sortsupport. Converts original uuid representation
+ * to abbreviated key representation. Our encoding strategy is simple -- pack
+ * the first `sizeof(Datum)` bytes of uuid data into a Datum (on little-endian
+ * machines, the bytes are stored in reverse order), and treat it as an
+ * unsigned integer.
+ */
+static Datum
+uuid_abbrev_convert(Datum original, SortSupport ssup)
+{
+ uuid_sortsupport_state *uss = ssup->ssup_extra;
+ pg_uuid_t *authoritative = DatumGetUUIDP(original);
+ Datum res;
+
+ memcpy((char *) &res, authoritative->data, sizeof(Datum));
+ uss->input_count += 1;
+
+ 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 uuid_cmp_abbrev() (an unsigned integer 3-way
+ * comparator) works correctly on all platforms. If we didn't do 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;
+}
+
/* hash index support */
Datum
uuid_hash(PG_FUNCTION_ARGS)
diff --git a/src/include/catalog/pg_amproc.h b/src/include/catalog/pg_amproc.h
index b57d6e65ca2..7db20154200 100644
--- a/src/include/catalog/pg_amproc.h
+++ b/src/include/catalog/pg_amproc.h
@@ -134,6 +134,7 @@ DATA(insert ( 2233 703 703 1 380 ));
DATA(insert ( 2234 704 704 1 381 ));
DATA(insert ( 2789 27 27 1 2794 ));
DATA(insert ( 2968 2950 2950 1 2960 ));
+DATA(insert ( 2968 2950 2950 2 3300 ));
DATA(insert ( 2994 2249 2249 1 2987 ));
DATA(insert ( 3194 2249 2249 1 3187 ));
DATA(insert ( 3253 3220 3220 1 3251 ));
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index f688454fbb3..26d189f561f 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -4467,6 +4467,8 @@ DATA(insert OID = 2958 ( uuid_gt PGNSP PGUID 12 1 0 0 0 f f f t t f i s 2 0
DATA(insert OID = 2959 ( uuid_ne PGNSP PGUID 12 1 0 0 0 f f f t t f i s 2 0 16 "2950 2950" _null_ _null_ _null_ _null_ _null_ uuid_ne _null_ _null_ _null_ ));
DATA(insert OID = 2960 ( uuid_cmp PGNSP PGUID 12 1 0 0 0 f f f f t f i s 2 0 23 "2950 2950" _null_ _null_ _null_ _null_ _null_ uuid_cmp _null_ _null_ _null_ ));
DESCR("less-equal-greater");
+DATA(insert OID = 3300 ( uuid_sortsupport PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 2278 "2281" _null_ _null_ _null_ _null_ _null_ uuid_sortsupport _null_ _null_ _null_ ));
+DESCR("sort support");
DATA(insert OID = 2961 ( uuid_recv PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 2950 "2281" _null_ _null_ _null_ _null_ _null_ uuid_recv _null_ _null_ _null_ ));
DESCR("I/O");
DATA(insert OID = 2962 ( uuid_send PGNSP PGUID 12 1 0 0 0 f f f f t f i s 1 0 17 "2950" _null_ _null_ _null_ _null_ _null_ uuid_send _null_ _null_ _null_ ));
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index c193e4425ed..130f5e23bcd 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -1174,6 +1174,7 @@ extern Datum uuid_ge(PG_FUNCTION_ARGS);
extern Datum uuid_gt(PG_FUNCTION_ARGS);
extern Datum uuid_ne(PG_FUNCTION_ARGS);
extern Datum uuid_cmp(PG_FUNCTION_ARGS);
+extern Datum uuid_sortsupport(PG_FUNCTION_ARGS);
extern Datum uuid_hash(PG_FUNCTION_ARGS);
/* windowfuncs.c */
--
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