Le mercredi 11 avril 2012 09:15:59, Sidney Cadot a écrit : > Dear all, > > As a hobby project, I am toying around with a database containing > about 5 million chess games. On average, these games have about 80 > positions (~ 40 moves by both black and white), which means there are > about 400 million chess positions in there. > > I have written code to extract these positions, and now I want to put > them into a Postgres database. Specifically, I want to do this in a > way that allows *fast* lookups of positions, e.g. "give me all > positions that have a White King on c4 and either a Black Bishop or > White Knight on f7". > > Currently, my "Positions" table looks like this: > > Column | Type | Modifiers > -------------------+---------+----------- > gameindex | integer | not null > plyindex | integer | not null > pseudofenboard | text | not null > fenside | text | not null > fencastling | text | not null > fenenpassant | text | not null > possiblemovecount | integer | not null > isincheck | boolean | not null > Indexes: > "positions_pkey" PRIMARY KEY, btree (gameindex, plyindex) > Foreign-key constraints: > "positions_gameindex_fkey" FOREIGN KEY (gameindex) REFERENCES > games(gameindex) > > The "PseudoFenBoard" field currently holds a string describing the > position. For example, the starting position of chess looks like this: > > "rnbqkbnr/pppppppp/________/________/________/________/PPPPPPPP/RNBQKBNR" > > This design allows me to formulate the kind of positional queries that > I want (by using regular expression matching), but executing them will > involve a slow, linear traversal of the 400M table rows, which is not > desirable. > > I am toying around with the ugly idea to make a "Positions" table that > has a single field for each of the squares, e.g. > > CREATE TABLE Position2 ( > GameIndex INTEGER NOT NULL, > PlyIndex INTEGER NOT NULL, > a1 "char" NOT NULL, > a2 "char" NOT NULL, > -- (60 fields defs omitted) > h7 "char" NOT NULL, > h8 "char" NOT NULL > ); > > This would allow the creation of indices on each of the 64 fields > separately, which should help to achieve near-instantaneous position > query performance, especially after gathering proper statistics for > all the field-specific indices. > > I realize that this design is quite ugly, so I would be interested to > hear if there are nicer alternatives that can perform equally well. > > Also, above I use the 1-byte "char" type. Is this the only type in > PostGres that is guaranteed to be just a single byte, or are there > better alternatives? A 13-state enum would be best (listing the 6 > white pieces, 6 black pieces, and 'empty' states for every square on > the board) but as I understand from the documentation, enums always up > take 4 bytes per entry. > > Any ideas for improvement would be greatly appreciated. I'll go test with BloomFiltering and multiple columns. http://www.sai.msu.su/~megera/wiki/bloom -- Cédric Villemain +33 (0)6 20 30 22 52 http://2ndQuadrant.fr/ PostgreSQL: Support 24x7 - Développement, Expertise et Formation -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
