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Teach pageinspect about nbtree deduplication.
Add a new bt_metap() column to display the metapage's allequalimage
field. Also add three new columns to contrib/pageinspect's
bt_page_items() function:
* Add a boolean column ("dead") that displays the LP_DEAD bit value for
each non-pivot tuple.
* Add a TID column ("htid") that displays a single heap TID value for
each tuple. This is the TID that is returned by BTreeTupleGetHeapTID(),
so comparable values are shown for pivot tuples, plain non-pivot tuples,
and posting list tuples.
* Add a TID array column ("tids") that displays TIDs from each tuple's
posting list, if any. This works just like the "tids" column from
pageinspect's gin_leafpage_items() function.
No version bump for the pageinspect extension, since there hasn't been a
stable Postgres release since the last version bump (the last bump was
part of commit 58b4cb30).
Author: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-WzmSMmU2eNvY9+a4MNP+z02h6sa-uxZvN3un6jY02ZVBSw@mail.gmail.com
This commit is contained in:
Peter Geoghegan
@ -300,13 +300,14 @@ test=# SELECT t_ctid, raw_flags, combined_flags
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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 | 3
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version | 4
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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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oldest_xact | 582
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last_cleanup_num_tuples | 1000
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allequalimage | f
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</screen>
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</para>
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</listitem>
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@ -329,11 +330,11 @@ 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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live_items | 224
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dead_items | 0
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avg_item_size | 12
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avg_item_size | 16
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page_size | 8192
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free_size | 4056
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free_size | 3668
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btpo_prev | 0
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btpo_next | 0
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btpo | 0
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@ -356,33 +357,75 @@ btpo_flags | 3
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<function>bt_page_items</function> returns detailed information about
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all of the items on a B-tree index page. For example:
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<screen>
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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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test=# SELECT itemoffset, ctid, itemlen, nulls, vars, data, dead, htid, tids[0:2] AS some_tids
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FROM bt_page_items(get_raw_page('tenk2_hundred', 5));
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itemoffset | ctid | itemlen | nulls | vars | data | dead | htid | some_tids
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------------+-----------+---------+-------+------+-------------------------+------+--------+---------------------
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1 | (16,1) | 16 | f | f | 30 00 00 00 00 00 00 00 | | |
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2 | (16,8292) | 616 | f | f | 24 00 00 00 00 00 00 00 | f | (1,6) | {"(1,6)","(10,22)"}
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3 | (16,8292) | 616 | f | f | 25 00 00 00 00 00 00 00 | f | (1,18) | {"(1,18)","(4,22)"}
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4 | (16,8292) | 616 | f | f | 26 00 00 00 00 00 00 00 | f | (4,18) | {"(4,18)","(6,17)"}
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5 | (16,8292) | 616 | f | f | 27 00 00 00 00 00 00 00 | f | (1,2) | {"(1,2)","(1,19)"}
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6 | (16,8292) | 616 | f | f | 28 00 00 00 00 00 00 00 | f | (2,24) | {"(2,24)","(4,11)"}
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7 | (16,8292) | 616 | f | f | 29 00 00 00 00 00 00 00 | f | (2,17) | {"(2,17)","(11,2)"}
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8 | (16,8292) | 616 | f | f | 2a 00 00 00 00 00 00 00 | f | (0,25) | {"(0,25)","(3,20)"}
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9 | (16,8292) | 616 | f | f | 2b 00 00 00 00 00 00 00 | f | (0,10) | {"(0,10)","(0,14)"}
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10 | (16,8292) | 616 | f | f | 2c 00 00 00 00 00 00 00 | f | (1,3) | {"(1,3)","(3,9)"}
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11 | (16,8292) | 616 | f | f | 2d 00 00 00 00 00 00 00 | f | (6,28) | {"(6,28)","(11,1)"}
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12 | (16,8292) | 616 | f | f | 2e 00 00 00 00 00 00 00 | f | (0,27) | {"(0,27)","(1,13)"}
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13 | (16,8292) | 616 | f | f | 2f 00 00 00 00 00 00 00 | f | (4,17) | {"(4,17)","(4,21)"}
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(13 rows)
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</screen>
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In a B-tree leaf page, <structfield>ctid</structfield> points to a heap tuple.
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In an internal page, the block number part of <structfield>ctid</structfield>
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points to another page in the index itself, while the offset part
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(the second number) is ignored and is usually 1.
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This is a B-tree leaf page. All tuples that point to the table
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happen to be posting list tuples (all of which store a total of
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100 6 byte TIDs). There is also a <quote>high key</quote> tuple
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at <literal>itemoffset</literal> number 1.
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<structfield>ctid</structfield> is used to store encoded
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information about each tuple in this example, though leaf page
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tuples often store a heap TID directly in the
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<structfield>ctid</structfield> field instead.
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<structfield>tids</structfield> is the list of TIDs stored as a
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posting list.
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</para>
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<para>
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In an internal page (not shown), the block number part of
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<structfield>ctid</structfield> is a <quote>downlink</quote>,
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which is a block number of another page in the index itself.
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The offset part (the second number) of
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<structfield>ctid</structfield> stores encoded information about
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the tuple, such as the number of columns present (suffix
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truncation may have removed unneeded suffix columns). Truncated
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columns are treated as having the value <quote>minus
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infinity</quote>.
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</para>
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<para>
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<structfield>htid</structfield> shows a heap TID for the tuple,
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regardless of the underlying tuple representation. This value
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may match <structfield>ctid</structfield>, or may be decoded
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from the alternative representations used by posting list tuples
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and tuples from internal pages. Tuples in internal pages
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usually have the implementation level heap TID column truncated
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away, which is represented as a NULL
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<structfield>htid</structfield> value.
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</para>
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<para>
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Note that the first item on any non-rightmost page (any page with
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a non-zero value in the <structfield>btpo_next</structfield> field) is the
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page's <quote>high key</quote>, meaning its <structfield>data</structfield>
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serves as an upper bound on all items appearing on the page, while
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its <structfield>ctid</structfield> field is meaningless. Also, on non-leaf
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pages, the first real data item (the first item that is not a high
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key) is a <quote>minus infinity</quote> item, with no actual value
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in its <structfield>data</structfield> field. Such an item does have a valid
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downlink in its <structfield>ctid</structfield> field, however.
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its <structfield>ctid</structfield> field does not point to
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another block. Also, on internal pages, the first real data
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item (the first item that is not a high key) reliably has every
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column truncated away, leaving no actual value in its
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<structfield>data</structfield> field. Such an item does have a
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valid downlink in its <structfield>ctid</structfield> field,
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however.
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</para>
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<para>
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For more details about the structure of B-tree indexes, see
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<xref linkend="btree-structure"/>. For more details about
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deduplication and posting lists, see <xref
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linkend="btree-deduplication"/>.
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</para>
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</listitem>
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</varlistentry>
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@ -402,17 +445,24 @@ test=# SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
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with <function>get_raw_page</function> should be passed as argument. So
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the last example could also be rewritten like this:
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<screen>
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test=# SELECT * FROM bt_page_items(get_raw_page('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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test=# SELECT itemoffset, ctid, itemlen, nulls, vars, data, dead, htid, tids[0:2] AS some_tids
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FROM bt_page_items(get_raw_page('tenk2_hundred', 5));
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itemoffset | ctid | itemlen | nulls | vars | data | dead | htid | some_tids
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------------+-----------+---------+-------+------+-------------------------+------+--------+---------------------
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1 | (16,1) | 16 | f | f | 30 00 00 00 00 00 00 00 | | |
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2 | (16,8292) | 616 | f | f | 24 00 00 00 00 00 00 00 | f | (1,6) | {"(1,6)","(10,22)"}
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3 | (16,8292) | 616 | f | f | 25 00 00 00 00 00 00 00 | f | (1,18) | {"(1,18)","(4,22)"}
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4 | (16,8292) | 616 | f | f | 26 00 00 00 00 00 00 00 | f | (4,18) | {"(4,18)","(6,17)"}
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5 | (16,8292) | 616 | f | f | 27 00 00 00 00 00 00 00 | f | (1,2) | {"(1,2)","(1,19)"}
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6 | (16,8292) | 616 | f | f | 28 00 00 00 00 00 00 00 | f | (2,24) | {"(2,24)","(4,11)"}
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7 | (16,8292) | 616 | f | f | 29 00 00 00 00 00 00 00 | f | (2,17) | {"(2,17)","(11,2)"}
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8 | (16,8292) | 616 | f | f | 2a 00 00 00 00 00 00 00 | f | (0,25) | {"(0,25)","(3,20)"}
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9 | (16,8292) | 616 | f | f | 2b 00 00 00 00 00 00 00 | f | (0,10) | {"(0,10)","(0,14)"}
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10 | (16,8292) | 616 | f | f | 2c 00 00 00 00 00 00 00 | f | (1,3) | {"(1,3)","(3,9)"}
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11 | (16,8292) | 616 | f | f | 2d 00 00 00 00 00 00 00 | f | (6,28) | {"(6,28)","(11,1)"}
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12 | (16,8292) | 616 | f | f | 2e 00 00 00 00 00 00 00 | f | (0,27) | {"(0,27)","(1,13)"}
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13 | (16,8292) | 616 | f | f | 2f 00 00 00 00 00 00 00 | f | (4,17) | {"(4,17)","(4,21)"}
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(13 rows)
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</screen>
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All the other details are the same as explained in the previous item.
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</para>
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