93 lines
3.0 KiB
PL/PgSQL
93 lines
3.0 KiB
PL/PgSQL
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CREATE OR REPLACE FUNCTION _CDB_Dummy_Ref_Z_Strategy(reloid REGCLASS)
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RETURNS INTEGER
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AS $$
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BEGIN
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-- TODO: should determine the proper *base* level for the table considering
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-- the density of features and precision/detail of the data,
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-- so that for Z levels equal or greater than the reference,
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-- the data can be represented clearly (without having to render uneccessary
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-- detail)
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RETURN 9;
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END;
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$$ LANGUAGE PLPGSQL STABLE;
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CREATE OR REPLACE FUNCTION _CDB_Overview_Name(ref REGCLASS, ref_z INTEGER, overview_z INTEGER)
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RETURNS TEXT
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AS $$
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DECLARE
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base TEXT;
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suffix TEXT;
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is_overview BOOLEAN;
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BEGIN
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suffix := Format('_ov%', ref_z);
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SELECT ref::text LIKE Format('%%%s', suffix) INTO is_overview;
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IF is_overview THEN
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SELECT substring(ref::text FROM 1 FOR length(ref::text)-length(suffix)) INTO base;
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ELSE
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base := ref;
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END IF;
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RETURN Format('%s_ov%s', base::text, overview_z);
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END
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$$ LANGUAGE PLPGSQL IMMUTABLE;
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CREATE OR REPLACE FUNCTION _CDB_Dummy_Reduce_Strategy(reloid REGCLASS, ref_z INTEGER, overview_z INTEGER)
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RETURNS REGCLASS
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AS $$
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DECLARE
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overview_rel TEXT;
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reduction FLOAT8;
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base_name TEXT;
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BEGIN
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overview_rel := _CDB_Overview_Name(reloid, ref_z, overview_z);
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-- TODO: implement a proper reduction technique.
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-- Here we're just inefficiently sampling the data to mantain
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-- the approximate visual density of the reference level.
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reduction := power(2, 2*(overview_z - ref_z));
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EXECUTE Format('DROP TABLE IF EXISTS %s CASCADE;', overview_rel);
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EXECUTE Format('CREATE TABLE %s AS SELECT * FROM %s WHERE random() < %s;', overview_rel, reloid, reduction);
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RETURN overview_rel;
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END;
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$$ LANGUAGE PLPGSQL;
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CREATE OR REPLACE FUNCTION CDB_CreateOverviews(
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reloid REGCLASS,
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refscale_strategy regproc DEFAULT '_CDB_Dummy_Ref_Z_Strategy'::regproc,
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reduce_strategy regproc DEFAULT '_CDB_Dummy_Reduce_Strategy'::regproc
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)
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RETURNS text[]
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AS $$
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DECLARE
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ref_z integer;
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overviews_z integer[];
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base_z integer;
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base_rel REGCLASS;
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overview_z integer;
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overview_tables REGCLASS[];
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BEGIN
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-- Determine the referece zoom level
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EXECUTE 'SELECT ' || quote_ident(refscale_strategy::text) || Format('(''%s'');', reloid) INTO ref_z;
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-- Determine overlay zoom levels
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-- TODO: should be handled by the refscale_stragegy?
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overview_z := ref_z - 1;
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WHILE overview_z >= 0 LOOP
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SELECT array_append(overviews_z, overview_z) INTO overviews_z;
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overview_z := overview_z - 2;
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END LOOP;
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-- Create overlay tables
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base_z := ref_z;
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base_rel := reloid;
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FOREACH overview_z IN ARRAY overviews_z LOOP
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EXECUTE 'SELECT ' || quote_ident(reduce_strategy::text) || Format('(''%s'', %s, %s);', base_rel, base_z, overview_z) INTO base_rel;
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SELECT array_append(overview_tables, base_rel) INTO overview_tables;
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END LOOP;
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-- TODO: we'll need to store metadata somewhere to define
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-- which overlay levels are available.
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RETURN overview_tables;
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END;
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$$ LANGUAGE PLPGSQL;
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