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The normal Postgres detoasting code locks and opens toast tables and indexes for each toast value, which can take a large percentage CPU time on simple queries. Since in decompression we're working with one table at a time, the toast table and index are the same for every datum, so we don't have to redo this work.
40 lines
1.7 KiB
PL/PgSQL
40 lines
1.7 KiB
PL/PgSQL
-- This file and its contents are licensed under the Timescale License.
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-- Please see the included NOTICE for copyright information and
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-- LICENSE-TIMESCALE for a copy of the license.
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-- Make a compressed table with a compressed string of varying length, to test
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-- the various ways the compressed data can be toasted.
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create table longstr(ts int default 1, s1 text);
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select create_hypertable('longstr', 'ts');
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alter table longstr set (timescaledb.compress);
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-- We want to test the case for inline compression. It is technically possible,
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-- but very hard to hit with the usual toast_tuple_target = 128 on compressed
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-- chunks. So here we increase the toast_tuple_target to simplify
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-- testing.
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select format('%I.%I', schema_name, table_name) compressed_table
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from _timescaledb_catalog.hypertable
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where id = (select compressed_hypertable_id from _timescaledb_catalog.hypertable
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where table_name = 'longstr')
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\gset
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alter table :compressed_table set (toast_tuple_target = 512);
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-- Now, test compression and decompression with various string lengths.
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create function test(repeats int, decompress bool) returns table(ns bigint) as $$ begin
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raise log 'repeats %', repeats;
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truncate longstr;
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insert into longstr(s1) select repeat('aaaa', repeats);
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perform count(compress_chunk(x, true)) from show_chunks('longstr') x;
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if decompress then
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perform decompress_chunk(x) from show_chunks('longstr') x;
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end if;
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return query select sum(length(s1)) from longstr;
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end; $$ language plpgsql volatile;
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select sum(t) from generate_series(1, 30) x, lateral test(x * x * x, false) t;
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-- Also test decompression which uses the detoaster as well.
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select sum(t) from generate_series(1, 30) x, lateral test(x * x * x, true) t;
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