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Use perfect hashing, instead of binary search, for keyword lookup.

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We've been speculating for a long time that hash-based keyword lookup
ought to be faster than binary search, but up to now we hadn't found
a suitable tool for generating the hash function.  Joerg Sonnenberger
provided the inspiration, and sample code, to show us that rolling our
own generator wasn't a ridiculous idea.  Hence, do that.

The method used here requires a lookup table of approximately 4 bytes
per keyword, but that's less than what we saved in the predecessor commit
afb0d0712, so it's not a big problem.  The time savings is indeed
significant: preliminary testing suggests that the total time for raw
parsing (flex + bison phases) drops by ~20%.

Patch by me, but it owes its existence to Joerg Sonnenberger;
thanks also to John Naylor for review.

Discussion: https://postgr.es/m/20190103163340.GA15803@britannica.bec.de
This commit is contained in:
Tom Lane
2019-01-09 19:47:38 -05:00
parent 5d59a6c5ea
commit c64d0cd5ce
14 changed files with 520 additions and 111 deletions
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10
src/tools/msvc/Solution.pm
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@@ -414,7 +414,7 @@ sub GenerateFiles
'src/include/parser/kwlist.h'))
{
print "Generating kwlist_d.h...\n";
system('perl src/tools/gen_keywordlist.pl --extern -o src/common src/include/parser/kwlist.h');
system('perl -I src/tools src/tools/gen_keywordlist.pl --extern -o src/common src/include/parser/kwlist.h');
}
if (IsNewer(
@@ -426,8 +426,8 @@ sub GenerateFiles
{
print "Generating pl_reserved_kwlist_d.h and pl_unreserved_kwlist_d.h...\n";
chdir('src/pl/plpgsql/src');
system('perl ../../../tools/gen_keywordlist.pl --varname ReservedPLKeywords pl_reserved_kwlist.h');
system('perl ../../../tools/gen_keywordlist.pl --varname UnreservedPLKeywords pl_unreserved_kwlist.h');
system('perl -I ../../../tools ../../../tools/gen_keywordlist.pl --varname ReservedPLKeywords pl_reserved_kwlist.h');
system('perl -I ../../../tools ../../../tools/gen_keywordlist.pl --varname UnreservedPLKeywords pl_unreserved_kwlist.h');
chdir('../../../..');
}
@@ -440,8 +440,8 @@ sub GenerateFiles
{
print "Generating c_kwlist_d.h and ecpg_kwlist_d.h...\n";
chdir('src/interfaces/ecpg/preproc');
system('perl ../../../tools/gen_keywordlist.pl --varname ScanCKeywords c_kwlist.h');
system('perl ../../../tools/gen_keywordlist.pl --varname ScanECPGKeywords ecpg_kwlist.h');
system('perl -I ../../../tools ../../../tools/gen_keywordlist.pl --varname ScanCKeywords --no-case-fold c_kwlist.h');
system('perl -I ../../../tools ../../../tools/gen_keywordlist.pl --varname ScanECPGKeywords ecpg_kwlist.h');
chdir('../../../..');
}