pageinspect The pageinspect module provides functions that allow you to inspect the contents of database pages at a low level, which is useful for debugging purposes. All of these functions may be used only by superusers. get_raw_page(relname text, fork text, blkno int) returns bytea get_raw_page get_raw_page reads the specified block of the named relation and returns a copy as a bytea value. This allows a single time-consistent copy of the block to be obtained. fork should be 'main' for the main data fork, 'fsm' for the free space map, 'vm' for the visibility map, or 'init' for the initialization fork. get_raw_page(relname text, blkno int) returns bytea A shorthand version of get_raw_page, for reading from the main fork. Equivalent to get_raw_page(relname, 'main', blkno) page_header(page bytea) returns record page_header page_header shows fields that are common to all PostgreSQL heap and index pages. A page image obtained with get_raw_page should be passed as argument. For example: test=# SELECT * FROM page_header(get_raw_page('pg_class', 0)); lsn | checksum | flags | lower | upper | special | pagesize | version | prune_xid -----------+----------+--------+-------+-------+---------+----------+---------+----------- 0/24A1B50 | 0 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0 The returned columns correspond to the fields in the PageHeaderData struct. See src/include/storage/bufpage.h for details. The checksum field is the checksum stored in the page, which might be incorrect if the page is somehow corrupted. If data checksums are not enabled for this instance, then the value stored is meaningless. page_checksum(page bytea, blkno int4) returns smallint page_checksum page_checksum computes the checksum for the page, as if it was located at the given block. A page image obtained with get_raw_page should be passed as argument. For example: test=# SELECT page_checksum(get_raw_page('pg_class', 0), 0); page_checksum --------------- 13443 Note that the checksum depends on the block number, so matching block numbers should be passed (except when doing esoteric debugging). The checksum computed with this function can be compared with the checksum result field of the function page_header. If data checksums are enabled for this instance, then the two values should be equal. fsm_page_contents(page bytea) returns text fsm_page_contents fsm_page_contents shows the internal node structure of a FSM page. For example: test=# SELECT fsm_page_contents(get_raw_page('pg_class', 'fsm', 0)); The output is a multiline string, with one line per node in the binary tree within the page. Only those nodes that are not zero are printed. The so-called "next" pointer, which points to the next slot to be returned from the page, is also printed. See src/backend/storage/freespace/README for more information on the structure of an FSM page. heap_page_items(page bytea) returns setof record heap_page_items heap_page_items shows all line pointers on a heap page. For those line pointers that are in use, tuple headers as well as tuple raw data are also shown. All tuples are shown, whether or not the tuples were visible to an MVCC snapshot at the time the raw page was copied. A heap page image obtained with get_raw_page should be passed as argument. For example: test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0)); See src/include/storage/itemid.h and src/include/access/htup_details.h for explanations of the fields returned. The heap_tuple_infomask_flags function can be used to unpack the flag bits of t_infomask and t_infomask2 for heap tuples. tuple_data_split(rel_oid oid, t_data bytea, t_infomask integer, t_infomask2 integer, t_bits text [, do_detoast bool]) returns bytea[] tuple_data_split tuple_data_split splits tuple data into attributes in the same way as backend internals. test=# SELECT tuple_data_split('pg_class'::regclass, t_data, t_infomask, t_infomask2, t_bits) FROM heap_page_items(get_raw_page('pg_class', 0)); This function should be called with the same arguments as the return attributes of heap_page_items. If do_detoast is true, attributes will be detoasted as needed. Default value is false. heap_page_item_attrs(page bytea, rel_oid regclass [, do_detoast bool]) returns setof record heap_page_item_attrs heap_page_item_attrs is equivalent to heap_page_items except that it returns tuple raw data as an array of attributes that can optionally be detoasted by do_detoast which is false by default. A heap page image obtained with get_raw_page should be passed as argument. For example: test=# SELECT * FROM heap_page_item_attrs(get_raw_page('pg_class', 0), 'pg_class'::regclass); heap_tuple_infomask_flags(t_infomask integer, t_infomask2 integer) returns record heap_tuple_infomask_flags heap_tuple_infomask_flags decodes the t_infomask and t_infomask2 returned by heap_page_items into a human-readable set of arrays made of flag names, with one column for all the flags and one column for combined flags. For example: test=# SELECT t_ctid, raw_flags, combined_flags FROM heap_page_items(get_raw_page('pg_class', 0)), LATERAL heap_tuple_infomask_flags(t_infomask, t_infomask2) WHERE t_infomask IS NOT NULL OR t_infomask2 IS NOT NULL; This function should be called with the same arguments as the return attributes of heap_page_items. Combined flags are displayed for source-level macros that take into account the value of more than one raw bit, such as HEAP_XMIN_FROZEN. See src/include/access/htup_details.h for explanations of the flag names returned. bt_metap(relname text) returns record bt_metap bt_metap returns information about a B-tree index's metapage. For example: test=# SELECT * FROM bt_metap('pg_cast_oid_index'); -[ RECORD 1 ]-----------+------- magic | 340322 version | 4 root | 1 level | 0 fastroot | 1 fastlevel | 0 oldest_xact | 582 last_cleanup_num_tuples | 1000 allequalimage | f bt_page_stats(relname text, blkno int) returns record bt_page_stats bt_page_stats returns summary information about single pages of B-tree indexes. For example: test=# SELECT * FROM bt_page_stats('pg_cast_oid_index', 1); -[ RECORD 1 ]-+----- blkno | 1 type | l live_items | 224 dead_items | 0 avg_item_size | 16 page_size | 8192 free_size | 3668 btpo_prev | 0 btpo_next | 0 btpo | 0 btpo_flags | 3 bt_page_items(relname text, blkno int) returns setof record bt_page_items bt_page_items returns detailed information about all of the items on a B-tree index page. For example: test=# SELECT itemoffset, ctid, itemlen, nulls, vars, data, dead, htid, tids[0:2] AS some_tids FROM bt_page_items('tenk2_hundred', 5); itemoffset | ctid | itemlen | nulls | vars | data | dead | htid | some_tids ------------+-----------+---------+-------+------+-------------------------+------+--------+--------------------- 1 | (16,1) | 16 | f | f | 30 00 00 00 00 00 00 00 | | | 2 | (16,8292) | 616 | f | f | 24 00 00 00 00 00 00 00 | f | (1,6) | {"(1,6)","(10,22)"} 3 | (16,8292) | 616 | f | f | 25 00 00 00 00 00 00 00 | f | (1,18) | {"(1,18)","(4,22)"} 4 | (16,8292) | 616 | f | f | 26 00 00 00 00 00 00 00 | f | (4,18) | {"(4,18)","(6,17)"} 5 | (16,8292) | 616 | f | f | 27 00 00 00 00 00 00 00 | f | (1,2) | {"(1,2)","(1,19)"} 6 | (16,8292) | 616 | f | f | 28 00 00 00 00 00 00 00 | f | (2,24) | {"(2,24)","(4,11)"} 7 | (16,8292) | 616 | f | f | 29 00 00 00 00 00 00 00 | f | (2,17) | {"(2,17)","(11,2)"} 8 | (16,8292) | 616 | f | f | 2a 00 00 00 00 00 00 00 | f | (0,25) | {"(0,25)","(3,20)"} 9 | (16,8292) | 616 | f | f | 2b 00 00 00 00 00 00 00 | f | (0,10) | {"(0,10)","(0,14)"} 10 | (16,8292) | 616 | f | f | 2c 00 00 00 00 00 00 00 | f | (1,3) | {"(1,3)","(3,9)"} 11 | (16,8292) | 616 | f | f | 2d 00 00 00 00 00 00 00 | f | (6,28) | {"(6,28)","(11,1)"} 12 | (16,8292) | 616 | f | f | 2e 00 00 00 00 00 00 00 | f | (0,27) | {"(0,27)","(1,13)"} 13 | (16,8292) | 616 | f | f | 2f 00 00 00 00 00 00 00 | f | (4,17) | {"(4,17)","(4,21)"} (13 rows) This is a B-tree leaf page. All tuples that point to the table happen to be posting list tuples (all of which store a total of 100 6 byte TIDs). There is also a high key tuple at itemoffset number 1. ctid is used to store encoded information about each tuple in this example, though leaf page tuples often store a heap TID directly in the ctid field instead. tids is the list of TIDs stored as a posting list. In an internal page (not shown), the block number part of ctid is a downlink, which is a block number of another page in the index itself. The offset part (the second number) of ctid stores encoded information about the tuple, such as the number of columns present (suffix truncation may have removed unneeded suffix columns). Truncated columns are treated as having the value minus infinity. htid shows a heap TID for the tuple, regardless of the underlying tuple representation. This value may match ctid, or may be decoded from the alternative representations used by posting list tuples and tuples from internal pages. Tuples in internal pages usually have the implementation level heap TID column truncated away, which is represented as a NULL htid value. Note that the first item on any non-rightmost page (any page with a non-zero value in the btpo_next field) is the page's high key, meaning its data serves as an upper bound on all items appearing on the page, while its ctid field does not point to another block. Also, on internal pages, the first real data item (the first item that is not a high key) reliably has every column truncated away, leaving no actual value in its data field. Such an item does have a valid downlink in its ctid field, however. For more details about the structure of B-tree indexes, see . For more details about deduplication and posting lists, see . bt_page_items(page bytea) returns setof record bt_page_items It is also possible to pass a page to bt_page_items as a bytea value. A page image obtained with get_raw_page should be passed as argument. So the last example could also be rewritten like this: test=# SELECT itemoffset, ctid, itemlen, nulls, vars, data, dead, htid, tids[0:2] AS some_tids FROM bt_page_items(get_raw_page('tenk2_hundred', 5)); itemoffset | ctid | itemlen | nulls | vars | data | dead | htid | some_tids ------------+-----------+---------+-------+------+-------------------------+------+--------+--------------------- 1 | (16,1) | 16 | f | f | 30 00 00 00 00 00 00 00 | | | 2 | (16,8292) | 616 | f | f | 24 00 00 00 00 00 00 00 | f | (1,6) | {"(1,6)","(10,22)"} 3 | (16,8292) | 616 | f | f | 25 00 00 00 00 00 00 00 | f | (1,18) | {"(1,18)","(4,22)"} 4 | (16,8292) | 616 | f | f | 26 00 00 00 00 00 00 00 | f | (4,18) | {"(4,18)","(6,17)"} 5 | (16,8292) | 616 | f | f | 27 00 00 00 00 00 00 00 | f | (1,2) | {"(1,2)","(1,19)"} 6 | (16,8292) | 616 | f | f | 28 00 00 00 00 00 00 00 | f | (2,24) | {"(2,24)","(4,11)"} 7 | (16,8292) | 616 | f | f | 29 00 00 00 00 00 00 00 | f | (2,17) | {"(2,17)","(11,2)"} 8 | (16,8292) | 616 | f | f | 2a 00 00 00 00 00 00 00 | f | (0,25) | {"(0,25)","(3,20)"} 9 | (16,8292) | 616 | f | f | 2b 00 00 00 00 00 00 00 | f | (0,10) | {"(0,10)","(0,14)"} 10 | (16,8292) | 616 | f | f | 2c 00 00 00 00 00 00 00 | f | (1,3) | {"(1,3)","(3,9)"} 11 | (16,8292) | 616 | f | f | 2d 00 00 00 00 00 00 00 | f | (6,28) | {"(6,28)","(11,1)"} 12 | (16,8292) | 616 | f | f | 2e 00 00 00 00 00 00 00 | f | (0,27) | {"(0,27)","(1,13)"} 13 | (16,8292) | 616 | f | f | 2f 00 00 00 00 00 00 00 | f | (4,17) | {"(4,17)","(4,21)"} (13 rows) All the other details are the same as explained in the previous item. brin_page_type(page bytea) returns text brin_page_type brin_page_type returns the page type of the given BRIN index page, or throws an error if the page is not a valid BRIN page. For example: test=# SELECT brin_page_type(get_raw_page('brinidx', 0)); brin_page_type ---------------- meta brin_metapage_info(page bytea) returns record brin_metapage_info brin_metapage_info returns assorted information about a BRIN index metapage. For example: test=# SELECT * FROM brin_metapage_info(get_raw_page('brinidx', 0)); magic | version | pagesperrange | lastrevmappage ------------+---------+---------------+---------------- 0xA8109CFA | 1 | 4 | 2 brin_revmap_data(page bytea) returns setof tid brin_revmap_data brin_revmap_data returns the list of tuple identifiers in a BRIN index range map page. For example: test=# SELECT * FROM brin_revmap_data(get_raw_page('brinidx', 2)) LIMIT 5; pages --------- (6,137) (6,138) (6,139) (6,140) (6,141) brin_page_items(page bytea, index oid) returns setof record brin_page_items brin_page_items returns the data stored in the BRIN data page. For example: test=# SELECT * FROM brin_page_items(get_raw_page('brinidx', 5), 'brinidx') ORDER BY blknum, attnum LIMIT 6; itemoffset | blknum | attnum | allnulls | hasnulls | placeholder | value ------------+--------+--------+----------+----------+-------------+-------------- 137 | 0 | 1 | t | f | f | 137 | 0 | 2 | f | f | f | {1 .. 88} 138 | 4 | 1 | t | f | f | 138 | 4 | 2 | f | f | f | {89 .. 176} 139 | 8 | 1 | t | f | f | 139 | 8 | 2 | f | f | f | {177 .. 264} The returned columns correspond to the fields in the BrinMemTuple and BrinValues structs. See src/include/access/brin_tuple.h for details. gin_metapage_info(page bytea) returns record gin_metapage_info gin_metapage_info returns information about a GIN index metapage. For example: test=# SELECT * FROM gin_metapage_info(get_raw_page('gin_index', 0)); -[ RECORD 1 ]----+----------- pending_head | 4294967295 pending_tail | 4294967295 tail_free_size | 0 n_pending_pages | 0 n_pending_tuples | 0 n_total_pages | 7 n_entry_pages | 6 n_data_pages | 0 n_entries | 693 version | 2 gin_page_opaque_info(page bytea) returns record gin_page_opaque_info gin_page_opaque_info returns information about a GIN index opaque area, like the page type. For example: test=# SELECT * FROM gin_page_opaque_info(get_raw_page('gin_index', 2)); rightlink | maxoff | flags -----------+--------+------------------------ 5 | 0 | {data,leaf,compressed} (1 row) gin_leafpage_items(page bytea) returns setof record gin_leafpage_items gin_leafpage_items returns information about the data stored in a GIN leaf page. For example: test=# SELECT first_tid, nbytes, tids[0:5] AS some_tids FROM gin_leafpage_items(get_raw_page('gin_test_idx', 2)); first_tid | nbytes | some_tids -----------+--------+---------------------------------------------------------- (8,41) | 244 | {"(8,41)","(8,43)","(8,44)","(8,45)","(8,46)"} (10,45) | 248 | {"(10,45)","(10,46)","(10,47)","(10,48)","(10,49)"} (12,52) | 248 | {"(12,52)","(12,53)","(12,54)","(12,55)","(12,56)"} (14,59) | 320 | {"(14,59)","(14,60)","(14,61)","(14,62)","(14,63)"} (167,16) | 376 | {"(167,16)","(167,17)","(167,18)","(167,19)","(167,20)"} (170,30) | 376 | {"(170,30)","(170,31)","(170,32)","(170,33)","(170,34)"} (173,44) | 197 | {"(173,44)","(173,45)","(173,46)","(173,47)","(173,48)"} (7 rows) hash_page_type(page bytea) returns text hash_page_type hash_page_type returns page type of the given HASH index page. For example: test=# SELECT hash_page_type(get_raw_page('con_hash_index', 0)); hash_page_type ---------------- metapage hash_page_stats(page bytea) returns setof record hash_page_stats hash_page_stats returns information about a bucket or overflow page of a HASH index. For example: test=# SELECT * FROM hash_page_stats(get_raw_page('con_hash_index', 1)); -[ RECORD 1 ]---+----------- live_items | 407 dead_items | 0 page_size | 8192 free_size | 8 hasho_prevblkno | 4096 hasho_nextblkno | 8474 hasho_bucket | 0 hasho_flag | 66 hasho_page_id | 65408 hash_page_items(page bytea) returns setof record hash_page_items hash_page_items returns information about the data stored in a bucket or overflow page of a HASH index page. For example: test=# SELECT * FROM hash_page_items(get_raw_page('con_hash_index', 1)) LIMIT 5; itemoffset | ctid | data ------------+-----------+------------ 1 | (899,77) | 1053474816 2 | (897,29) | 1053474816 3 | (894,207) | 1053474816 4 | (892,159) | 1053474816 5 | (890,111) | 1053474816 hash_bitmap_info(index oid, blkno int) returns record hash_bitmap_info hash_bitmap_info shows the status of a bit in the bitmap page for a particular overflow page of HASH index. For example: test=# SELECT * FROM hash_bitmap_info('con_hash_index', 2052); bitmapblkno | bitmapbit | bitstatus -------------+-----------+----------- 65 | 3 | t hash_metapage_info(page bytea) returns record hash_metapage_info hash_metapage_info returns information stored in the meta page of a HASH index. For example: test=# SELECT magic, version, ntuples, ffactor, bsize, bmsize, bmshift, test-# maxbucket, highmask, lowmask, ovflpoint, firstfree, nmaps, procid, test-# regexp_replace(spares::text, '(,0)*}', '}') as spares, test-# regexp_replace(mapp::text, '(,0)*}', '}') as mapp test-# FROM hash_metapage_info(get_raw_page('con_hash_index', 0)); -[ RECORD 1 ]-------------------------------------------------&zwsp;------------------------------ magic | 105121344 version | 4 ntuples | 500500 ffactor | 40 bsize | 8152 bmsize | 4096 bmshift | 15 maxbucket | 12512 highmask | 16383 lowmask | 8191 ovflpoint | 28 firstfree | 1204 nmaps | 1 procid | 450 spares | {0,0,0,0,0,0,1,1,1,1,1,1,1,1,3,4,4,4,45,55,58,59,&zwsp;508,567,628,704,1193,1202,1204} mapp | {65}