From 741afead540b219a2a3e82f0db6840e8ff93b0eb Mon Sep 17 00:00:00 2001 From: John Naylor Date: Wed, 26 Dec 2018 21:34:34 -0500 Subject: [PATCH v4 2/2] Dispatch keyword lookup on the first character. In addition, use heuristics to improve chances of skipping binary search. For each legal keyword character where it makes sense, choose a common keyword and use its index for the first middle index of binary search. --- src/common/keywords.c | 30 ++++++++++--- src/include/common/keywords.h | 10 ++++- src/pl/plpgsql/src/pl_scanner.c | 6 +-- src/tools/gen_keywords.pl | 78 +++++++++++++++++++++++++++++++++ 4 files changed, 114 insertions(+), 10 deletions(-) diff --git a/src/common/keywords.c b/src/common/keywords.c index b0e5a721b6..207bc4274f 100644 --- a/src/common/keywords.c +++ b/src/common/keywords.c @@ -118,12 +118,14 @@ int ScanKeywordLookupOffset(const char *string_to_lookup, const char *kw_strings, const uint16 *kw_offsets, - int num_keywords) + const ScanKeywordRange *kw_ranges) { int len, - i; + i, + range_idx; char word[NAMEDATALEN]; const uint16 *low; + const uint16 *middle; const uint16 *high; len = strlen(string_to_lookup); @@ -145,17 +147,32 @@ ScanKeywordLookupOffset(const char *string_to_lookup, } word[len] = '\0'; + /* XXX assumes keywords can't start with '_' */ + range_idx = (int) word[0] - 'a'; + + if (word[0] < 'a' || word[0] > 'z' + || kw_ranges[range_idx].lower == PG_UINT16_MAX) + return -1; + /* * Now do a binary search using plain strcmp() comparison. */ - low = kw_offsets; - high = kw_offsets + (num_keywords - 1); + low = kw_offsets + kw_ranges[range_idx].lower; + high = kw_offsets + kw_ranges[range_idx].upper; + + if (kw_ranges[range_idx].middle != PG_UINT16_MAX) + { + middle = kw_offsets + kw_ranges[range_idx].middle; + } + else + { + middle = low + (high - low) / 2; + } + while (low <= high) { - const uint16 *middle; int difference; - middle = low + (high - low) / 2; difference = strcmp(kw_strings + *middle, word); if (difference == 0) return middle - kw_offsets; @@ -163,6 +180,7 @@ ScanKeywordLookupOffset(const char *string_to_lookup, low = middle + 1; else high = middle - 1; + middle = low + (high - low) / 2; } return -1; diff --git a/src/include/common/keywords.h b/src/include/common/keywords.h index 201d0fcc7a..348773c682 100644 --- a/src/include/common/keywords.h +++ b/src/include/common/keywords.h @@ -35,6 +35,14 @@ typedef struct ScanKeywordAux char category; /* see codes above */ } ScanKeywordAux; +/* Lower and upper indexes, and first guess, for a range of keywords. */ +typedef struct ScanKeywordRange +{ + uint16 lower; + uint16 middle; + uint16 upper; +} ScanKeywordRange; + #ifndef FRONTEND extern PGDLLIMPORT const ScanKeyword ScanKeywords[]; extern PGDLLIMPORT const int NumScanKeywords; @@ -51,6 +59,6 @@ extern const ScanKeyword *ScanKeywordLookup(const char *text, int ScanKeywordLookupOffset(const char *string_to_lookup, const char *kw_strings, const uint16 *kw_offsets, - int num_keywords); + const ScanKeywordRange *kw_ranges); #endif /* KEYWORDS_H */ diff --git a/src/pl/plpgsql/src/pl_scanner.c b/src/pl/plpgsql/src/pl_scanner.c index 0b2f331117..808bf465a0 100644 --- a/src/pl/plpgsql/src/pl_scanner.c +++ b/src/pl/plpgsql/src/pl_scanner.c @@ -261,7 +261,7 @@ plpgsql_yylex(void) (kwnum = ScanKeywordLookupOffset(aux1.lval.word.ident, pl_unreserved_kw_strings, pl_unreserved_kw_offsets, - num_unreserved_keywords)) >= 0) + pl_unreserved_kw_ranges)) >= 0) { aux1.lval.keyword = pl_unreserved_kw_strings + pl_unreserved_kw_offsets[kwnum]; @@ -293,7 +293,7 @@ plpgsql_yylex(void) (kwnum = ScanKeywordLookupOffset(aux1.lval.str, pl_unreserved_kw_strings, pl_unreserved_kw_offsets, - num_unreserved_keywords)) >= 0) + pl_unreserved_kw_ranges)) >= 0) { aux1.lval.keyword = pl_unreserved_kw_strings + pl_unreserved_kw_offsets[kwnum]; @@ -319,7 +319,7 @@ plpgsql_yylex(void) (kwnum = ScanKeywordLookupOffset(aux1.lval.word.ident, pl_unreserved_kw_strings, pl_unreserved_kw_offsets, - num_unreserved_keywords)) >= 0) + pl_unreserved_kw_ranges)) >= 0) { aux1.lval.keyword = pl_unreserved_kw_strings + pl_unreserved_kw_offsets[kwnum]; diff --git a/src/tools/gen_keywords.pl b/src/tools/gen_keywords.pl index 1faa14ffca..6678bfc72f 100644 --- a/src/tools/gen_keywords.pl +++ b/src/tools/gen_keywords.pl @@ -99,6 +99,84 @@ for my $i (0..$#keywords - 1) if ($keywords[$i] cmp $keywords[$i + 1]) >= 0; } +# These are the most common core keywords for each letter of the alphabet, +# if there is a clear winner, preferably near the middle of the range. +my %FIRST_GUESS = ( + and => 1, + commit => 1, # demo for WIP, since it's a plpgsql unreserved keyword + delete => 1, + exists => 1, + from => 1, + group => 1, + having => 1, + in => 1, + join => 1, + limit => 1, + not => 1, + or => 1, + select => 1, + then => 1, + update => 1, + values => 1, + where => 1, +); + +# Save the min and max indexes and a first guess middle index for each range +# of keywords starting with the same first character. +my $index = 0; +my $lower = 0; +my $middle; +my $first = 1; +my $curr_char = substr($keywords[0], 0, 1); +my %range; +foreach my $name (@keywords) +{ + if (substr($name, 0, 1) ne $curr_char) + { + $range{$curr_char} = {lower => $lower, middle => $middle, upper => $index}; + + # Set values for next range. + $curr_char = substr($name, 0, 1); + $index++; + $lower = $index; + $middle = undef; + } + elsif ($first == 1) + { + $first = 0; + } + else + { + $index++; + } + + # Save the index if the keyword is our first guess for the current + # first character. + if (exists $FIRST_GUESS{$name}) + { + $middle = $index; + } +} + +# Save last member of the list. +$range{$curr_char} = {lower => $lower, middle => $middle, upper => $index}; + +# Emit array of the upper, middle and lower indexes that we saved earlier. +# To keep the array small, we count from 'a', the lowest character that can +# start a keyword. +# XXX assumes keywords can't start with '_' +printf $kwdef "static const ScanKeywordRange %skw_ranges[] = {\n\t", $prefix; +foreach my $c ('a'..'z') +{ + my $char = $range{$c}; + + printf $kwdef "{%s, %s, %s},\n\t", + defined($char->{lower}) ? $char->{lower} : 'PG_UINT16_MAX', + defined($char->{middle}) ? $char->{middle} : 'PG_UINT16_MAX', + defined($char->{upper}) ? $char->{upper} : 'PG_UINT16_MAX', +} +print $kwdef "};\n\n"; + # Emit an array of numerical offsets which will be used to index into the # keyword string. printf $kwdef "static const uint16 %skw_offsets[] = {\n\t", $prefix; -- 2.17.1