diff options
Diffstat (limited to 'doc/src/sgml/pageinspect.sgml')
| -rw-r--r-- | doc/src/sgml/pageinspect.sgml | 822 |
1 files changed, 822 insertions, 0 deletions
diff --git a/doc/src/sgml/pageinspect.sgml b/doc/src/sgml/pageinspect.sgml new file mode 100644 index 0000000..ac5caa6 --- /dev/null +++ b/doc/src/sgml/pageinspect.sgml @@ -0,0 +1,822 @@ +<!-- doc/src/sgml/pageinspect.sgml --> + +<sect1 id="pageinspect" xreflabel="pageinspect"> + <title>pageinspect</title> + + <indexterm zone="pageinspect"> + <primary>pageinspect</primary> + </indexterm> + + <para> + The <filename>pageinspect</filename> 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. + </para> + + <sect2> + <title>General Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>get_raw_page(relname text, fork text, blkno int) returns bytea</function> + <indexterm> + <primary>get_raw_page</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>get_raw_page</function> reads the specified block of the named + relation and returns a copy as a <type>bytea</type> value. This allows a + single time-consistent copy of the block to be obtained. + <replaceable>fork</replaceable> should be <literal>'main'</literal> for + the main data fork, <literal>'fsm'</literal> for the free space map, + <literal>'vm'</literal> for the visibility map, or <literal>'init'</literal> + for the initialization fork. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>get_raw_page(relname text, blkno int) returns bytea</function> + </term> + + <listitem> + <para> + A shorthand version of <function>get_raw_page</function>, for reading + from the main fork. Equivalent to + <literal>get_raw_page(relname, 'main', blkno)</literal> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>page_header(page bytea) returns record</function> + <indexterm> + <primary>page_header</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>page_header</function> shows fields that are common to all + <productname>PostgreSQL</productname> heap and index pages. + </para> + + <para> + A page image obtained with <function>get_raw_page</function> should be + passed as argument. For example: +<screen> +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 +</screen> + The returned columns correspond to the fields in the + <structname>PageHeaderData</structname> struct. + See <filename>src/include/storage/bufpage.h</filename> for details. + </para> + + <para> + The <structfield>checksum</structfield> 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. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>page_checksum(page bytea, blkno int4) returns smallint</function> + <indexterm> + <primary>page_checksum</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>page_checksum</function> computes the checksum for the page, as if + it was located at the given block. + </para> + + <para> + A page image obtained with <function>get_raw_page</function> should be + passed as argument. For example: +<screen> +test=# SELECT page_checksum(get_raw_page('pg_class', 0), 0); + page_checksum +--------------- + 13443 +</screen> + Note that the checksum depends on the block number, so matching block + numbers should be passed (except when doing esoteric debugging). + </para> + + <para> + The checksum computed with this function can be compared with + the <structfield>checksum</structfield> result field of the + function <function>page_header</function>. If data checksums are + enabled for this instance, then the two values should be equal. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>fsm_page_contents(page bytea) returns text</function> + <indexterm> + <primary>fsm_page_contents</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>fsm_page_contents</function> shows the internal node structure + of a FSM page. For example: +<screen> +test=# SELECT fsm_page_contents(get_raw_page('pg_class', 'fsm', 0)); +</screen> + 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. + </para> + <para> + See <filename>src/backend/storage/freespace/README</filename> for more + information on the structure of an FSM page. + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2> + <title>Heap Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>heap_page_items(page bytea) returns setof record</function> + <indexterm> + <primary>heap_page_items</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>heap_page_items</function> 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. + </para> + <para> + A heap page image obtained with <function>get_raw_page</function> should + be passed as argument. For example: +<screen> +test=# SELECT * FROM heap_page_items(get_raw_page('pg_class', 0)); +</screen> + See <filename>src/include/storage/itemid.h</filename> and + <filename>src/include/access/htup_details.h</filename> for explanations of the fields + returned. + </para> + <para> + The <function>heap_tuple_infomask_flags</function> function can be + used to unpack the flag bits of <structfield>t_infomask</structfield> + and <structfield>t_infomask2</structfield> for heap tuples. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>tuple_data_split(rel_oid oid, t_data bytea, t_infomask integer, t_infomask2 integer, t_bits text [, do_detoast bool]) returns bytea[]</function> + <indexterm> + <primary>tuple_data_split</primary> + </indexterm> + </term> + <listitem> + <para> + <function>tuple_data_split</function> splits tuple data into attributes + in the same way as backend internals. +<screen> +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)); +</screen> + This function should be called with the same arguments as the return + attributes of <function>heap_page_items</function>. + </para> + <para> + If <parameter>do_detoast</parameter> is <literal>true</literal>, + attributes will be detoasted as needed. Default value is + <literal>false</literal>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>heap_page_item_attrs(page bytea, rel_oid regclass [, do_detoast bool]) returns setof record</function> + <indexterm> + <primary>heap_page_item_attrs</primary> + </indexterm> + </term> + <listitem> + <para> + <function>heap_page_item_attrs</function> is equivalent to + <function>heap_page_items</function> except that it returns + tuple raw data as an array of attributes that can optionally + be detoasted by <parameter>do_detoast</parameter> which is + <literal>false</literal> by default. + </para> + <para> + A heap page image obtained with <function>get_raw_page</function> should + be passed as argument. For example: +<screen> +test=# SELECT * FROM heap_page_item_attrs(get_raw_page('pg_class', 0), 'pg_class'::regclass); +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>heap_tuple_infomask_flags(t_infomask integer, t_infomask2 integer) returns record</function> + <indexterm> + <primary>heap_tuple_infomask_flags</primary> + </indexterm> + </term> + <listitem> + <para> + <function>heap_tuple_infomask_flags</function> decodes the + <structfield>t_infomask</structfield> and + <structfield>t_infomask2</structfield> returned by + <function>heap_page_items</function> 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: +<screen> +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; +</screen> + This function should be called with the same arguments as the return + attributes of <function>heap_page_items</function>. + </para> + <para> + Combined flags are displayed for source-level macros that take into + account the value of more than one raw bit, such as + <literal>HEAP_XMIN_FROZEN</literal>. + </para> + <para> + See <filename>src/include/access/htup_details.h</filename> for + explanations of the flag names returned. + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2> + <title>B-Tree Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>bt_metap(relname text) returns record</function> + <indexterm> + <primary>bt_metap</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>bt_metap</function> returns information about a B-tree + index's metapage. For example: +<screen> +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 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>bt_page_stats(relname text, blkno int) returns record</function> + <indexterm> + <primary>bt_page_stats</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>bt_page_stats</function> returns summary information about + single pages of B-tree indexes. For example: +<screen> +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 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>bt_page_items(relname text, blkno int) returns setof record</function> + <indexterm> + <primary>bt_page_items</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>bt_page_items</function> returns detailed information about + all of the items on a B-tree index page. For example: +<screen> +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) +</screen> + 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 <quote>high key</quote> tuple + at <literal>itemoffset</literal> number 1. + <structfield>ctid</structfield> is used to store encoded + information about each tuple in this example, though leaf page + tuples often store a heap TID directly in the + <structfield>ctid</structfield> field instead. + <structfield>tids</structfield> is the list of TIDs stored as a + posting list. + </para> + <para> + In an internal page (not shown), the block number part of + <structfield>ctid</structfield> is a <quote>downlink</quote>, + which is a block number of another page in the index itself. + The offset part (the second number) of + <structfield>ctid</structfield> 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 <quote>minus + infinity</quote>. + </para> + <para> + <structfield>htid</structfield> shows a heap TID for the tuple, + regardless of the underlying tuple representation. This value + may match <structfield>ctid</structfield>, 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 + <structfield>htid</structfield> value. + </para> + <para> + Note that the first item on any non-rightmost page (any page with + a non-zero value in the <structfield>btpo_next</structfield> field) is the + page's <quote>high key</quote>, meaning its <structfield>data</structfield> + serves as an upper bound on all items appearing on the page, while + its <structfield>ctid</structfield> 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 + <structfield>data</structfield> field. Such an item does have a + valid downlink in its <structfield>ctid</structfield> field, + however. + </para> + <para> + For more details about the structure of B-tree indexes, see + <xref linkend="btree-structure"/>. For more details about + deduplication and posting lists, see <xref + linkend="btree-deduplication"/>. + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>bt_page_items(page bytea) returns setof record</function> + <indexterm> + <primary>bt_page_items</primary> + </indexterm> + </term> + + <listitem> + <para> + It is also possible to pass a page to <function>bt_page_items</function> + as a <type>bytea</type> value. A page image obtained + with <function>get_raw_page</function> should be passed as argument. So + the last example could also be rewritten like this: +<screen> +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) +</screen> + All the other details are the same as explained in the previous item. + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2> + <title>BRIN Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>brin_page_type(page bytea) returns text</function> + <indexterm> + <primary>brin_page_type</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>brin_page_type</function> returns the page type of the given + <acronym>BRIN</acronym> index page, or throws an error if the page is + not a valid <acronym>BRIN</acronym> page. For example: +<screen> +test=# SELECT brin_page_type(get_raw_page('brinidx', 0)); + brin_page_type +---------------- + meta +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>brin_metapage_info(page bytea) returns record</function> + <indexterm> + <primary>brin_metapage_info</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>brin_metapage_info</function> returns assorted information + about a <acronym>BRIN</acronym> index metapage. For example: +<screen> +test=# SELECT * FROM brin_metapage_info(get_raw_page('brinidx', 0)); + magic | version | pagesperrange | lastrevmappage +------------+---------+---------------+---------------- + 0xA8109CFA | 1 | 4 | 2 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>brin_revmap_data(page bytea) returns setof tid</function> + <indexterm> + <primary>brin_revmap_data</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>brin_revmap_data</function> returns the list of tuple + identifiers in a <acronym>BRIN</acronym> index range map page. + For example: +<screen> +test=# SELECT * FROM brin_revmap_data(get_raw_page('brinidx', 2)) LIMIT 5; + pages +--------- + (6,137) + (6,138) + (6,139) + (6,140) + (6,141) +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>brin_page_items(page bytea, index oid) returns setof record</function> + <indexterm> + <primary>brin_page_items</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>brin_page_items</function> returns the data stored in the + <acronym>BRIN</acronym> data page. For example: +<screen> +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} +</screen> + The returned columns correspond to the fields in the + <structname>BrinMemTuple</structname> and <structname>BrinValues</structname> structs. + See <filename>src/include/access/brin_tuple.h</filename> for details. + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2> + <title>GIN Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>gin_metapage_info(page bytea) returns record</function> + <indexterm> + <primary>gin_metapage_info</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>gin_metapage_info</function> returns information about + a <acronym>GIN</acronym> index metapage. For example: +<screen> +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 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>gin_page_opaque_info(page bytea) returns record</function> + <indexterm> + <primary>gin_page_opaque_info</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>gin_page_opaque_info</function> returns information about + a <acronym>GIN</acronym> index opaque area, like the page type. + For example: +<screen> +test=# SELECT * FROM gin_page_opaque_info(get_raw_page('gin_index', 2)); + rightlink | maxoff | flags +-----------+--------+------------------------ + 5 | 0 | {data,leaf,compressed} +(1 row) +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>gin_leafpage_items(page bytea) returns setof record</function> + <indexterm> + <primary>gin_leafpage_items</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>gin_leafpage_items</function> returns information about + the data stored in a <acronym>GIN</acronym> leaf page. For example: +<screen> +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) +</screen> + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + + <sect2> + <title>Hash Functions</title> + + <variablelist> + <varlistentry> + <term> + <function>hash_page_type(page bytea) returns text</function> + <indexterm> + <primary>hash_page_type</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>hash_page_type</function> returns page type of + the given <acronym>HASH</acronym> index page. For example: +<screen> +test=# SELECT hash_page_type(get_raw_page('con_hash_index', 0)); + hash_page_type +---------------- + metapage +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>hash_page_stats(page bytea) returns setof record</function> + <indexterm> + <primary>hash_page_stats</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>hash_page_stats</function> returns information about + a bucket or overflow page of a <acronym>HASH</acronym> index. + For example: +<screen> +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 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>hash_page_items(page bytea) returns setof record</function> + <indexterm> + <primary>hash_page_items</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>hash_page_items</function> returns information about + the data stored in a bucket or overflow page of a <acronym>HASH</acronym> + index page. For example: +<screen> +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 +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>hash_bitmap_info(index oid, blkno int) returns record</function> + <indexterm> + <primary>hash_bitmap_info</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>hash_bitmap_info</function> shows the status of a bit + in the bitmap page for a particular overflow page of <acronym>HASH</acronym> + index. For example: +<screen> +test=# SELECT * FROM hash_bitmap_info('con_hash_index', 2052); + bitmapblkno | bitmapbit | bitstatus +-------------+-----------+----------- + 65 | 3 | t +</screen> + </para> + </listitem> + </varlistentry> + + <varlistentry> + <term> + <function>hash_metapage_info(page bytea) returns record</function> + <indexterm> + <primary>hash_metapage_info</primary> + </indexterm> + </term> + + <listitem> + <para> + <function>hash_metapage_info</function> returns information stored + in the meta page of a <acronym>HASH</acronym> index. For example: +<screen> +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} +</screen> + </para> + </listitem> + </varlistentry> + </variablelist> + </sect2> + +</sect1> |