Re: gsoc, oprrest function for text search take 2 - Mailing list pgsql-hackers

Jan Urbański wrote:
> Heikki Linnakangas wrote:
>> Jan Urbański wrote:
>>> So right now the idea is to:
>>>  (1) pre-sort STATISTIC_KIND_MCELEM values
>>>  (2) build an array of pointers to detoasted values in tssel()
>>>  (3) use binary search when looking for MCELEMs during tsquery analysis
>>
>> Sounds like a plan. In (2), it's even better to detoast the values
>> lazily. For a typical one-word tsquery, the binary search will only
>> look at a small portion of the elements.
>
> Here's another version.

Context diff this time, always forget to convert them...

--
Jan Urbanski
GPG key ID: E583D7D2

ouden estin
*** a/src/backend/tsearch/Makefile
--- b/src/backend/tsearch/Makefile
***************
*** 19,25 **** DICTFILES=synonym_sample.syn thesaurus_sample.ths hunspell_sample.affix \
  OBJS = ts_locale.o ts_parse.o wparser.o wparser_def.o dict.o \
      dict_simple.o dict_synonym.o dict_thesaurus.o \
      dict_ispell.o regis.o spell.o \
!     to_tsany.o ts_typanalyze.o ts_utils.o

  include $(top_srcdir)/src/backend/common.mk

--- 19,25 ----
  OBJS = ts_locale.o ts_parse.o wparser.o wparser_def.o dict.o \
      dict_simple.o dict_synonym.o dict_thesaurus.o \
      dict_ispell.o regis.o spell.o \
!     to_tsany.o ts_typanalyze.o ts_selfuncs.o ts_utils.o

  include $(top_srcdir)/src/backend/common.mk

*** /dev/null
--- b/src/backend/tsearch/ts_selfuncs.c
***************
*** 0 ****
--- 1,320 ----
+ /*-------------------------------------------------------------------------
+  *
+  * ts_selfuncs.c
+  *      Selectivity functions for text search types.
+  *
+  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
+  *
+  *
+  * IDENTIFICATION
+  *      $PostgreSQL$
+  *
+  *-------------------------------------------------------------------------
+  */
+ #include "postgres.h"
+
+ #include "miscadmin.h" /* for check_stack_depth() */
+ #include "utils/memutils.h"
+ #include "utils/builtins.h"
+ #include "utils/syscache.h"
+ #include "utils/lsyscache.h"
+ #include "utils/selfuncs.h"
+ #include "catalog/pg_type.h"
+ #include "catalog/pg_statistic.h"
+ #include "nodes/nodes.h"
+ #include "tsearch/ts_type.h"
+
+ /* lookup table type for binary searching through MCELEMs */
+ typedef struct
+ {
+     Datum    element;
+     float4    frequency;
+ } TextFreq;
+
+ /* type of keys for bsearch()ing through an array of TextFreqs  */
+ typedef struct
+ {
+     char    *lexeme;
+     int        length;
+ } LexemeKey;
+
+ static int
+ compare_lexeme_textfreq(const void *e1, const void *e2);
+
+ static Selectivity
+ tsquery_opr_selec(QueryItem *item, char *operand, TextFreq *lookup,
+                   int length, float4 minfreq);
+ static Selectivity
+ mcelem_tsquery_selec(TSQuery query, Datum *mcelem, int nmcelem,
+                            float4 *numbers, int nnumbers);
+ static double
+ tsquerysel(VariableStatData *vardata, Datum constval);
+
+
+ /* TSQuery traversal function */
+ static Selectivity
+ tsquery_opr_selec(QueryItem *item, char *operand, TextFreq *lookup,
+                   int length, float4 minfreq)
+ {
+     LexemeKey    key;
+     TextFreq    *searchres;
+     Selectivity    s1, s2;
+
+     /* since this function recurses, it could be driven to stack overflow */
+     check_stack_depth();
+
+     if (item->type == QI_VAL)
+     {
+         QueryOperand *oper = (QueryOperand *) item;
+
+         /*
+          * Prepare the key for bsearch().
+          */
+         key.lexeme = operand + oper->distance;
+         key.length = oper->length;
+
+         searchres = (TextFreq *) bsearch(&key, lookup, length,
+                                          sizeof(TextFreq), compare_lexeme_textfreq);
+
+         if (searchres)
+         {
+             /*
+              * The element is in MCELEM. Return precise selectivity (or at
+              * least as precise, as ANALYZE could find out).
+              */
+             return (Selectivity) searchres->frequency;
+         }
+         else
+         {
+             /*
+              * The element is not in MCELEM. Punt, but assert that the
+              * selectivity cannot be more than minfreq / 2.
+              */
+             return (Selectivity) Min(DEFAULT_TS_SEL, minfreq / 2);
+         }
+     }
+
+     /* Current TSQuery node is an operator */
+     switch (item->operator.oper)
+     {
+         case OP_NOT:
+             return 1.0 - tsquery_opr_selec(item + 1, operand, lookup,
+                                            length, minfreq);
+
+         case OP_AND:
+             return
+                 tsquery_opr_selec(item + 1, operand, lookup, length, minfreq) *
+                 tsquery_opr_selec(item + item->operator.left, operand, lookup,
+                                   length, minfreq);
+
+         case OP_OR:
+             s1 = tsquery_opr_selec(item + 1, operand, lookup, length, minfreq);
+             s2 = tsquery_opr_selec(item + item->operator.left, operand, lookup,
+                                    length, minfreq);
+             return s1 + s2 - s1 * s2;
+
+         default:
+             elog(ERROR, "unrecognized operator: %d", item->operator.oper);
+     }
+
+     /* never reached, keep compiler happy */
+     return (Selectivity) DEFAULT_TS_SEL;
+ }
+
+ /*
+  * Traverse the tsquery preorder, calculating selectivity as:
+  *
+  *   selec(left_oper) * selec(right_oper) in AND nodes,
+  *
+  *   selec(left_oper) + selec(right_oper) -
+  *      selec(left_oper) * selec(right_oper) in OR nodes,
+  *
+  *   1 - select(oper) in NOT nodes
+  *
+  *   freq[val] in VAL nodes, if the value is in MCELEM
+  *   min(freq[MCELEM]) / 2 in VAL nodes, if it is not
+  *
+  *
+  * The MCELEM array is already sorted (see ts_typanalyze.c), so we can use
+  * binary search for determining freq[MCELEM].
+  */
+ static Selectivity
+ mcelem_tsquery_selec(TSQuery query, Datum *mcelem, int nmcelem,
+                            float4 *numbers, int nnumbers)
+ {
+     float4            minfreq;
+     TextFreq        *lookup;
+     Selectivity        selec;
+     int                i;
+
+     /* Grab the lowest frequency */
+
+     /*
+       XXX This is no longer easy, need to go through the whole list. Plug it
+       with 2.0 for the moment (so that minfreq / 2 is 1.0)
+
+       minfreq = numbers[nnumbers - 1];
+     */
+     minfreq = 2.0;
+
+     /* Construct the array for binary search */
+     Assert(nmcelem == nnumbers);
+     lookup = (TextFreq *) palloc(sizeof(TextFreq) * nmcelem);
+     for (i = 0; i < nmcelem; i++)
+     {
+         lookup[i].element = mcelem[i];
+         lookup[i].frequency = numbers[i];
+     }
+
+     selec = tsquery_opr_selec(GETQUERY(query), GETOPERAND(query), lookup,
+                               nmcelem, minfreq);
+
+     pfree(lookup);
+
+     return selec;
+ }
+
+ /*
+  * bsearch() comparator for a lexeme (non-NULL terminated string with length)
+  * and a TextFreq. Use length, then byte-for-byte comparision, because that's
+  * how ANALYZE code sorted data before storing it in a statistic tuple.
+  * See ts_typanalyze.c for details.
+  */
+ static int
+ compare_lexeme_textfreq(const void *e1, const void *e2)
+ {
+     const LexemeKey    *key;
+     const TextFreq    *t;
+     text            *element;
+     int                len1,
+                     len2;
+
+     key = (const LexemeKey *) e1;
+     t = (const TextFreq *) e2;
+
+     len1 = key->length;
+     len2 = VARSIZE_ANY_EXHDR(t->element);
+
+     /* Compare lengths first, possibly avoiding pointless detoasting */
+     if (len1 > len2)
+         return 1;
+     else if (len1 < len2)
+         return -1;
+
+     /* Fall back on byte-for-byte comparision, detoasting the Datum first */
+     element = DatumGetTextP(t->element);
+
+     return strncmp(key->lexeme, VARDATA_ANY(element), len1);
+ }
+
+ /*
+  *    tssel -- Selectivity of "@@"
+  */
+ Datum
+ tssel(PG_FUNCTION_ARGS)
+ {
+     PlannerInfo        *root = (PlannerInfo *) PG_GETARG_POINTER(0);
+     /* We skip arg #2, which is the operator OID - it's gonna be "@@" */
+     List            *args = (List *) PG_GETARG_POINTER(2);
+     int                varRelid = PG_GETARG_INT32(3);
+     VariableStatData vardata;
+     Node            *other;
+     bool            varonleft;
+     Selectivity        selec;
+
+     /*
+      * If expression is not variable op something or something op variable,
+      * then punt and return a default estimate.
+      */
+     if (!get_restriction_variable(root, args, varRelid,
+                                   &vardata, &other, &varonleft))
+     {
+         PG_RETURN_FLOAT8(DEFAULT_TS_SEL);
+     }
+
+     /*
+      * Can't do anything useful if the something is not a constant, either.
+      */
+     if (!IsA(other, Const))
+     {
+         ReleaseVariableStats(vardata);
+         PG_RETURN_FLOAT8(DEFAULT_TS_SEL);
+     }
+
+     /* The "@@" operator is strict, so might cope with NULL right away */
+     if (((Const *) other)->constisnull) {
+         ReleaseVariableStats(vardata);
+         PG_RETURN_FLOAT8((float8) 0.0);
+     }
+
+     /*
+      * OK, there's a Var and a Const we're dealing with here. We need the Var
+      * to be a TSVector (or else we don't have any useful statistic for it).
+      */
+
+     if (vardata.vartype == TSVECTOROID)
+     {
+         /* tsvector @@ tsquery or the other way around */
+         Assert(((Const *) other)->consttype == TSQUERYOID);
+
+         selec = tsquerysel(&vardata, ((Const *) other)->constvalue);
+     }
+     else
+     {
+         /* The Var is something we don't have useful statistic for */
+         selec = DEFAULT_TS_SEL;
+     }
+
+     ReleaseVariableStats(vardata);
+
+     PG_RETURN_FLOAT8((float8) selec);
+ }
+
+ static Selectivity
+ tsquerysel(VariableStatData *vardata, Datum constval)
+ {
+     Selectivity            selec;
+
+     if (HeapTupleIsValid(vardata->statsTuple))
+     {
+         TSQuery                query;
+         Form_pg_statistic    stats;
+         Datum                *values;
+         int                    nvalues;
+         float4                *numbers;
+         int                    nnumbers;
+
+         /* The caller made sure the const is a TSQuery, so get it now */
+         query = DatumGetTSQuery(constval);
+
+         stats = (Form_pg_statistic) GETSTRUCT(vardata->statsTuple);
+
+         /* MCELEM will be an array of Text elements for a tsvector column */
+         if (get_attstatsslot(vardata->statsTuple,
+                              TEXTOID, -1,
+                              STATISTIC_KIND_MCELEM, InvalidOid,
+                              &values, &nvalues,
+                              &numbers, &nnumbers))
+         {
+             /*
+              * There is a most-common-elements slot for the tsvector Var, so
+              * use that.
+              */
+
+             selec = mcelem_tsquery_selec(query, values, nvalues,
+                                          numbers, nnumbers);
+             free_attstatsslot(TEXTOID, values, nvalues, numbers, nnumbers);
+         }
+         else
+         {
+             /* No most-common-elements slot */
+             selec = (Selectivity) DEFAULT_TS_SEL;
+         }
+     }
+     else
+     {
+         selec = (Selectivity) DEFAULT_TS_SEL;
+     }
+
+     return selec;
+ }
*** a/src/backend/tsearch/ts_typanalyze.c
--- b/src/backend/tsearch/ts_typanalyze.c
***************
*** 43,50 **** static void compute_tsvector_stats(VacAttrStats *stats,
  static void prune_lexemes_hashtable(HTAB *lexemes_tab, int b_current);
  static uint32 lexeme_hash(const void *key, Size keysize);
  static int lexeme_match(const void *key1, const void *key2, Size keysize);
! static int trackitem_compare_desc(const void *e1, const void *e2);
!

  /*
   *    ts_typanalyze -- a custom typanalyze function for tsvector columns
--- 43,51 ----
  static void prune_lexemes_hashtable(HTAB *lexemes_tab, int b_current);
  static uint32 lexeme_hash(const void *key, Size keysize);
  static int lexeme_match(const void *key1, const void *key2, Size keysize);
! static int lexeme_compare(const void *key1, const void *key2);
! static int trackitem_compare_frequencies_desc(const void *e1, const void *e2);
! static int trackitem_compare_lexemes(const void *e1, const void *e2);

  /*
   *    ts_typanalyze -- a custom typanalyze function for tsvector columns
***************
*** 273,279 **** compute_tsvector_stats(VacAttrStats *stats,
          Assert(i == track_len);

          qsort(sort_table, track_len, sizeof(TrackItem *),
!               trackitem_compare_desc);

          /* Suppress any single-occurrence items */
          while (track_len > 0)
--- 274,280 ----
          Assert(i == track_len);

          qsort(sort_table, track_len, sizeof(TrackItem *),
!               trackitem_compare_frequencies_desc);

          /* Suppress any single-occurrence items */
          while (track_len > 0)
***************
*** 287,292 **** compute_tsvector_stats(VacAttrStats *stats,
--- 288,309 ----
          if (num_mcelem > track_len)
              num_mcelem = track_len;

+         /*
+          * We want to store statistics sorted on the lexeme value using first
+          * length, then byte-for-byte comparision. The reason for doing length
+          * comparision first is that we don't care about the ordering as long
+          * as it's consistent and comparing lengths first gives us a chance to
+          * avoid a strncmp() call.
+          *
+          * This is different from what we do with scalar statistics -- they get
+          * sorted on frequencies. The rationale is that we usually search
+          * through most common elements looking for a specific value, so we can
+          * grab its frequency. When values are presorted we can employ binary
+          * search for that. See ts_selfuncs.c for a real usage scenario.
+          */
+         qsort(sort_table, num_mcelem, sizeof(TrackItem *),
+               trackitem_compare_lexemes);
+
          /* Generate MCELEM slot entry */
          if (num_mcelem > 0)
          {
***************
*** 379,403 **** lexeme_hash(const void *key, Size keysize)
  static int
  lexeme_match(const void *key1, const void *key2, Size keysize)
  {
!     const LexemeHashKey *d1 = (const LexemeHashKey *) key1;
!     const LexemeHashKey *d2 = (const LexemeHashKey *) key2;

!     /* The lexemes need to have the same length, and be memcmp-equal */
!     if (d1->length == d2->length &&
!         memcmp(d1->lexeme, d2->lexeme, d1->length) == 0)
!         return 0;
!     else
          return 1;
  }

  /*
!  *    qsort() comparator for TrackItems - LC style (descending sort)
   */
  static int
! trackitem_compare_desc(const void *e1, const void *e2)
  {
      const TrackItem * const *t1 = (const TrackItem * const *) e1;
      const TrackItem * const *t2 = (const TrackItem * const *) e2;

      return (*t2)->frequency - (*t1)->frequency;
  }
--- 396,444 ----
  static int
  lexeme_match(const void *key1, const void *key2, Size keysize)
  {
!     /* The keysize parameter is superfluous, the keys store their lengths */
!     return lexeme_compare(key1, key2);
! }

! /*
!  *    Comparision function for lexemes.
!  */
! static int
! lexeme_compare(const void *key1, const void *key2)
! {
!     const LexemeHashKey    *d1 = (const LexemeHashKey *) key1;
!     const LexemeHashKey    *d2 = (const LexemeHashKey *) key2;
!
!     /* First, compare by length */
!     if (d1->length > d2->length)
          return 1;
+     else if (d1->length < d2->length)
+         return -1;
+     else
+         /* Lengths are equal, do a byte-for-byte comparision */
+         return strncmp(d1->lexeme, d2->lexeme, d1->length);
  }

  /*
!  *    qsort() comparator for sorting TrackItems on frequencies (descending sort)
   */
  static int
! trackitem_compare_frequencies_desc(const void *e1, const void *e2)
  {
      const TrackItem * const *t1 = (const TrackItem * const *) e1;
      const TrackItem * const *t2 = (const TrackItem * const *) e2;

      return (*t2)->frequency - (*t1)->frequency;
  }
+
+ /*
+  *    qsort() comparator for sorting TrackItem on lexemes
+  */
+ static int
+ trackitem_compare_lexemes(const void *e1, const void *e2)
+ {
+     const TrackItem * const *t1 = (const TrackItem * const *) e1;
+     const TrackItem * const *t2 = (const TrackItem * const *) e2;
+
+     return lexeme_compare(&(*t1)->key, &(*t2)->key);
+ }
*** a/src/include/catalog/pg_operator.h
--- b/src/include/catalog/pg_operator.h
***************
*** 915,924 **** DATA(insert OID = 3630 (  "<>"       PGNSP PGUID b f f 3614     3614     16 3630 3629     ts
  DATA(insert OID = 3631 (  ">="       PGNSP PGUID b f f 3614     3614     16 3628 3627     tsvector_ge scalargtsel
scalargtjoinsel)); 
  DATA(insert OID = 3632 (  ">"       PGNSP PGUID b f f 3614     3614     16 3627 3628     tsvector_gt scalargtsel
scalargtjoinsel)); 
  DATA(insert OID = 3633 (  "||"       PGNSP PGUID b f f 3614     3614     3614  0    0     tsvector_concat   -    -
 )); 
! DATA(insert OID = 3636 (  "@@"       PGNSP PGUID b f f 3614     3615     16 3637    0     ts_match_vq   contsel
contjoinsel    )); 
! DATA(insert OID = 3637 (  "@@"       PGNSP PGUID b f f 3615     3614     16 3636    0     ts_match_qv   contsel
contjoinsel    )); 
! DATA(insert OID = 3660 (  "@@@"    PGNSP PGUID b f f 3614     3615     16 3661    0     ts_match_vq   contsel
contjoinsel    )); 
! DATA(insert OID = 3661 (  "@@@"    PGNSP PGUID b f f 3615     3614     16 3660    0     ts_match_qv   contsel
contjoinsel    )); 
  DATA(insert OID = 3674 (  "<"       PGNSP PGUID b f f 3615     3615     16 3679 3678     tsquery_lt scalarltsel
scalarltjoinsel)); 
  DATA(insert OID = 3675 (  "<="       PGNSP PGUID b f f 3615     3615     16 3678 3679     tsquery_le scalarltsel
scalarltjoinsel)); 
  DATA(insert OID = 3676 (  "="       PGNSP PGUID b t f 3615     3615     16 3676 3677     tsquery_eq eqsel eqjoinsel
));
--- 915,924 ----
  DATA(insert OID = 3631 (  ">="       PGNSP PGUID b f f 3614     3614     16 3628 3627     tsvector_ge scalargtsel
scalargtjoinsel)); 
  DATA(insert OID = 3632 (  ">"       PGNSP PGUID b f f 3614     3614     16 3627 3628     tsvector_gt scalargtsel
scalargtjoinsel)); 
  DATA(insert OID = 3633 (  "||"       PGNSP PGUID b f f 3614     3614     3614  0    0     tsvector_concat   -    -
 )); 
! DATA(insert OID = 3636 (  "@@"       PGNSP PGUID b f f 3614     3615     16 3637    0     ts_match_vq   tssel
contjoinsel    )); 
! DATA(insert OID = 3637 (  "@@"       PGNSP PGUID b f f 3615     3614     16 3636    0     ts_match_qv   tssel
contjoinsel    )); 
! DATA(insert OID = 3660 (  "@@@"    PGNSP PGUID b f f 3614     3615     16 3661    0     ts_match_vq   tssel
contjoinsel    )); 
! DATA(insert OID = 3661 (  "@@@"    PGNSP PGUID b f f 3615     3614     16 3660    0     ts_match_qv   tssel
contjoinsel    )); 
  DATA(insert OID = 3674 (  "<"       PGNSP PGUID b f f 3615     3615     16 3679 3678     tsquery_lt scalarltsel
scalarltjoinsel)); 
  DATA(insert OID = 3675 (  "<="       PGNSP PGUID b f f 3615     3615     16 3678 3679     tsquery_le scalarltsel
scalarltjoinsel)); 
  DATA(insert OID = 3676 (  "="       PGNSP PGUID b t f 3615     3615     16 3676 3677     tsquery_eq eqsel eqjoinsel
));
*** a/src/include/catalog/pg_proc.h
--- b/src/include/catalog/pg_proc.h
***************
*** 4321,4326 **** DESCR("GiST tsquery support");
--- 4321,4328 ----
  DATA(insert OID = 3701 (  gtsquery_consistent            PGNSP PGUID 12 1 0 0 f f t f i 5 16 "2281 2281 23 26 2281"
_null__null_ _null_ gtsquery_consistent _null_ _null_ _null_ )); 
  DESCR("GiST tsquery support");

+ DATA(insert OID = 3687 (  tssel    PGNSP PGUID 12 1 0 0 f f t f s 4 701 "2281 26 2281 23" _null_ _null_ _null_ tssel
_null__null_ _null_ )); 
+ DESCR("restriction selectivity of tsvector @@ tsquery");
  DATA(insert OID = 3688 (  ts_typanalyze    PGNSP PGUID 12 1 0 0 f f t f s 1 16 "2281" _null_ _null_ _null_
ts_typanalyze_null_ _null_ _null_ )); 
  DESCR("tsvector typanalyze");

*** a/src/include/tsearch/ts_type.h
--- b/src/include/tsearch/ts_type.h
***************
*** 155,160 **** extern Datum ts_rankcd_wttf(PG_FUNCTION_ARGS);
--- 155,162 ----

  extern Datum ts_typanalyze(PG_FUNCTION_ARGS);

+ extern Datum tssel(PG_FUNCTION_ARGS);
+

  /*
   * TSQuery
***************
*** 291,294 **** extern Datum tsquery_rewrite_query(PG_FUNCTION_ARGS);
--- 293,309 ----
  extern Datum tsq_mcontains(PG_FUNCTION_ARGS);
  extern Datum tsq_mcontained(PG_FUNCTION_ARGS);

+ /*
+  * The default text search selectivity is chosen to be smll enough to
+  * encourage indexscans for typical table densities. See selfuncs.h and
+  * DEFAULT_EQ_SEL for details.
+  */
+ #define DEFAULT_TS_SEL 0.005
+
+ /*
+  * operator restriction function for tsvector @@ tsquery and
+  * tsquery @@ tsvector
+  */
+ extern Datum tssel(PG_FUNCTION_ARGS);
+
  #endif   /* _PG_TSTYPE_H_ */