95 lines
3.4 KiB
Plaintext
95 lines
3.4 KiB
Plaintext
The functions in this module allow you to inspect the contents of data pages
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at a low level, for debugging purposes. All of these functions may be used
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only by superusers.
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1. Installation
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$ make
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$ make install
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$ psql -e -f /usr/local/pgsql/share/contrib/pageinspect.sql test
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2. Functions included:
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get_raw_page
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------------
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get_raw_page reads one block of the named table and returns a copy as a
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bytea field. This allows a single time-consistent copy of the block to be
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made.
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page_header
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-----------
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page_header shows fields which are common to all PostgreSQL heap and index
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pages.
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A page image obtained with get_raw_page should be passed as argument:
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regression=# SELECT * FROM page_header(get_raw_page('pg_class',0));
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lsn | tli | flags | lower | upper | special | pagesize | version | prune_xid
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-----------+-----+-------+-------+-------+---------+----------+---------+-----------
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0/24A1B50 | 1 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0
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(1 row)
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The returned columns correspond to the fields in the PageHeaderData struct.
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See src/include/storage/bufpage.h for details.
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heap_page_items
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---------------
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heap_page_items shows all line pointers on a heap page. For those line
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pointers that are in use, tuple headers are also shown. All tuples are
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shown, whether or not the tuples were visible to an MVCC snapshot at the
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time the raw page was copied.
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A heap page image obtained with get_raw_page should be passed as argument:
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test=# SELECT * FROM heap_page_items(get_raw_page('pg_class',0));
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See src/include/storage/itemid.h and src/include/access/htup.h for
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explanations of the fields returned.
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bt_metap
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--------
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bt_metap() returns information about a btree index's metapage:
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test=> SELECT * FROM bt_metap('pg_cast_oid_index');
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-[ RECORD 1 ]-----
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magic | 340322
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version | 2
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root | 1
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level | 0
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fastroot | 1
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fastlevel | 0
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bt_page_stats
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-------------
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bt_page_stats() shows information about single btree pages:
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test=> SELECT * FROM bt_page_stats('pg_cast_oid_index', 1);
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-[ RECORD 1 ]-+-----
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blkno | 1
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type | l
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live_items | 256
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dead_items | 0
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avg_item_size | 12
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page_size | 8192
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free_size | 4056
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btpo_prev | 0
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btpo_next | 0
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btpo | 0
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btpo_flags | 3
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bt_page_items
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-------------
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bt_page_items() returns information about specific items on btree pages:
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test=> SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
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itemoffset | ctid | itemlen | nulls | vars | data
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------------+---------+---------+-------+------+-------------
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1 | (0,1) | 12 | f | f | 23 27 00 00
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2 | (0,2) | 12 | f | f | 24 27 00 00
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3 | (0,3) | 12 | f | f | 25 27 00 00
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4 | (0,4) | 12 | f | f | 26 27 00 00
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5 | (0,5) | 12 | f | f | 27 27 00 00
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6 | (0,6) | 12 | f | f | 28 27 00 00
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7 | (0,7) | 12 | f | f | 29 27 00 00
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8 | (0,8) | 12 | f | f | 2a 27 00 00
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