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Previously, all heaps had FSMs. For very small tables, this means that the FSM took up more space than the heap did. This is wasteful, so now we refrain from creating the FSM for heaps with 4 pages or fewer. If the last known target block has insufficient space, we still try to insert into some other page before giving up and extending the relation, since doing otherwise leads to table bloat. Testing showed that trying every page penalized performance slightly, so we compromise and try every other page. This way, we visit at most two pages. Any pages with wasted free space become visible at next relation extension, so we still control table bloat. As a bonus, directly attempting one or two pages can even be faster than consulting the FSM would have been. Once the FSM is created for a heap we don't remove it even if somebody deletes all the rows from the corresponding relation. We don't think it is a useful optimization as it is quite likely that relation will again grow to the same size. Author: John Naylor with design inputs and some code contribution by Amit Kapila Reviewed-by: Amit Kapila Tested-by: Mithun C Y Discussion: https://www.postgresql.org/message-id/CAJVSVGWvB13PzpbLEecFuGFc5V2fsO736BsdTakPiPAcdMM5tQ@mail.gmail.com
117 lines
4.0 KiB
Plaintext
117 lines
4.0 KiB
Plaintext
CREATE EXTENSION pageinspect;
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CREATE TABLE test_rel_forks (a int);
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-- Make sure there are enough blocks in the heap for the FSM to be created.
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INSERT INTO test_rel_forks SELECT i from generate_series(1,1000) i;
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-- set up FSM and VM
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VACUUM test_rel_forks;
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-- The page contents can vary, so just test that it can be read
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-- successfully, but don't keep the output.
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SELECT octet_length(get_raw_page('test_rel_forks', 'main', 0)) AS main_0;
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main_0
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--------
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8192
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(1 row)
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SELECT octet_length(get_raw_page('test_rel_forks', 'main', 100)) AS main_100;
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ERROR: block number 100 is out of range for relation "test_rel_forks"
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SELECT octet_length(get_raw_page('test_rel_forks', 'fsm', 0)) AS fsm_0;
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fsm_0
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-------
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8192
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(1 row)
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SELECT octet_length(get_raw_page('test_rel_forks', 'fsm', 10)) AS fsm_10;
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ERROR: block number 10 is out of range for relation "test_rel_forks"
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SELECT octet_length(get_raw_page('test_rel_forks', 'vm', 0)) AS vm_0;
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vm_0
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------
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8192
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(1 row)
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SELECT octet_length(get_raw_page('test_rel_forks', 'vm', 1)) AS vm_1;
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ERROR: block number 1 is out of range for relation "test_rel_forks"
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SELECT octet_length(get_raw_page('xxx', 'main', 0));
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ERROR: relation "xxx" does not exist
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SELECT octet_length(get_raw_page('test_rel_forks', 'xxx', 0));
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ERROR: invalid fork name
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HINT: Valid fork names are "main", "fsm", "vm", and "init".
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SELECT * FROM fsm_page_contents(get_raw_page('test_rel_forks', 'fsm', 0));
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fsm_page_contents
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-------------------
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0: 147 +
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1: 147 +
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3: 147 +
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7: 147 +
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15: 147 +
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31: 147 +
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63: 147 +
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127: 147 +
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255: 147 +
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511: 147 +
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1023: 147 +
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2047: 147 +
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4095: 147 +
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fp_next_slot: 0 +
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(1 row)
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SELECT get_raw_page('test_rel_forks', 0) = get_raw_page('test_rel_forks', 'main', 0);
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?column?
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----------
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t
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(1 row)
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DROP TABLE test_rel_forks;
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CREATE TABLE test1 (a int, b int);
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INSERT INTO test1 VALUES (16777217, 131584);
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SELECT pagesize, version FROM page_header(get_raw_page('test1', 0));
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pagesize | version
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----------+---------
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8192 | 4
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(1 row)
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SELECT page_checksum(get_raw_page('test1', 0), 0) IS NOT NULL AS silly_checksum_test;
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silly_checksum_test
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---------------------
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t
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(1 row)
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SELECT tuple_data_split('test1'::regclass, t_data, t_infomask, t_infomask2, t_bits)
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FROM heap_page_items(get_raw_page('test1', 0));
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tuple_data_split
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-------------------------------
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{"\\x01000001","\\x00020200"}
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(1 row)
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DROP TABLE test1;
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-- check that using any of these functions with a partitioned table or index
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-- would fail
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create table test_partitioned (a int) partition by range (a);
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create index test_partitioned_index on test_partitioned (a);
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select get_raw_page('test_partitioned', 0); -- error about partitioned table
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ERROR: cannot get raw page from partitioned table "test_partitioned"
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select get_raw_page('test_partitioned_index', 0); -- error about partitioned index
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ERROR: cannot get raw page from partitioned index "test_partitioned_index"
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-- a regular table which is a member of a partition set should work though
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create table test_part1 partition of test_partitioned for values from ( 1 ) to (100);
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select get_raw_page('test_part1', 0); -- get farther and error about empty table
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ERROR: block number 0 is out of range for relation "test_part1"
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drop table test_partitioned;
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-- check null bitmap alignment for table whose number of attributes is multiple of 8
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create table test8 (f1 int, f2 int, f3 int, f4 int, f5 int, f6 int, f7 int, f8 int);
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insert into test8(f1, f8) values (x'7f00007f'::int, 0);
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select t_bits, t_data from heap_page_items(get_raw_page('test8', 0));
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t_bits | t_data
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----------+--------------------
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10000001 | \x7f00007f00000000
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(1 row)
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select tuple_data_split('test8'::regclass, t_data, t_infomask, t_infomask2, t_bits)
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from heap_page_items(get_raw_page('test8', 0));
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tuple_data_split
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-------------------------------------------------------------
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{"\\x7f00007f",NULL,NULL,NULL,NULL,NULL,NULL,"\\x00000000"}
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(1 row)
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drop table test8;
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