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187 lines
6.4 KiB
Plaintext
187 lines
6.4 KiB
Plaintext
This utility allows administrators to examine the file structure used by
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PostgreSQL.
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Databases are placed in directories named after their OIDs in pg_database,
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and the table files within a database's directory are named by "filenode"
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numbers, which are stored in pg_class.relfilenode.
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Note that while a table's filenode often matches its OID, this is *not*
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necessarily the case; some operations, like TRUNCATE, REINDEX, CLUSTER
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and some forms of ALTER TABLE, can change the filenode while preserving
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the OID. Avoid assuming that filenode and table OID are the same.
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When a table exceeds 1Gb, it is divided into gigabyte-sized "segments".
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The first segment's file name is the same as the filenode; subsequent
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segments are named filenode.1, filenode.2, etc.
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Tablespaces make the scenario more complicated. Each non-default
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tablespace has a symlink inside the pg_tblspc directory, which points to
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the physical tablespace directory (as specified in its CREATE TABLESPACE
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command). The symlink is named after the tablespace's OID. Inside the
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physical tablespace directory there is another directory for each database
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that has elements in the tablespace, named after the database's OID.
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Tables within that directory follow the filenode naming scheme. The
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"pg_default" tablespace is not addressed via pg_tblspc, but corresponds to
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$PGDATA/base.
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Oid2name connects to the database and extracts OID, filenode, and table
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name information. You can also have it show database OIDs and tablespace
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OIDs.
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When displaying specific tables, you can select which tables to show by
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using -o, -f and -t. The first switch takes an OID, the second takes
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a filenode, and the third takes a tablename (actually, it's a LIKE
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pattern, so you can use things like "foo%"). Note that you can use as many
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of these switches as you like, and the listing will include all objects
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matched by any of the switches. Also note that these switches can only
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show objects in the database given in -d.
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If you don't give any of -o, -f or -t it will dump all the tables in the
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database given in -d. If you don't give -d, it will show a database
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listing. Alternatively you can give -s to get a tablespace listing.
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Additional switches:
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-i include indexes and sequences in the database listing.
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-x display more information about each object shown:
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tablespace name, schema name, OID.
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-S also show system objects
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(those in information_schema, pg_toast and pg_catalog schemas)
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-q don't display headers
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(useful for scripting)
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---------------------------------------------------------------------------
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Sample session:
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$ oid2name
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All databases:
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Oid Database Name Tablespace
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----------------------------------
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17228 alvherre pg_default
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17255 regression pg_default
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17227 template0 pg_default
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1 template1 pg_default
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$ oid2name -s
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All tablespaces:
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Oid Tablespace Name
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-------------------------
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1663 pg_default
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1664 pg_global
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155151 fastdisk
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155152 bigdisk
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$ cd $PGDATA/17228
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$ # get top 10 db objects in the default tablespace, ordered by size
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$ ls -lS * | head -10
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-rw------- 1 alvherre alvherre 136536064 sep 14 09:51 155173
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-rw------- 1 alvherre alvherre 17965056 sep 14 09:51 1155291
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-rw------- 1 alvherre alvherre 1204224 sep 14 09:51 16717
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-rw------- 1 alvherre alvherre 581632 sep 6 17:51 1255
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-rw------- 1 alvherre alvherre 237568 sep 14 09:50 16674
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-rw------- 1 alvherre alvherre 212992 sep 14 09:51 1249
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-rw------- 1 alvherre alvherre 204800 sep 14 09:51 16684
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-rw------- 1 alvherre alvherre 196608 sep 14 09:50 16700
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-rw------- 1 alvherre alvherre 163840 sep 14 09:50 16699
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-rw------- 1 alvherre alvherre 122880 sep 6 17:51 16751
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$ oid2name -d alvherre -f 155173
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From database "alvherre":
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Filenode Table Name
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----------------------
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155173 accounts
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$ # you can ask for more than one object
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$ oid2name -d alvherre -f 155173 -f 1155291
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From database "alvherre":
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Filenode Table Name
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-------------------------
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155173 accounts
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1155291 accounts_pkey
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$ # you can also mix the options, and have more details
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$ oid2name -d alvherre -t accounts -f 1155291 -x
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From database "alvherre":
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Filenode Table Name Oid Schema Tablespace
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------------------------------------------------------
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155173 accounts 155173 public pg_default
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1155291 accounts_pkey 1155291 public pg_default
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$ # show disk space for every db object
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$ du [0-9]* |
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> while read SIZE FILENODE
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> do
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> echo "$SIZE `oid2name -q -d alvherre -i -f $FILENODE`"
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> done
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16 1155287 branches_pkey
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16 1155289 tellers_pkey
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17561 1155291 accounts_pkey
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...
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$ # same, but sort by size
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$ du [0-9]* | sort -rn | while read SIZE FN
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> do
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> echo "$SIZE `oid2name -q -d alvherre -f $FN`"
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> done
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133466 155173 accounts
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17561 1155291 accounts_pkey
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1177 16717 pg_proc_proname_args_nsp_index
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...
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$ # If you want to see what's in tablespaces, use the pg_tblspc directory
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$ cd $PGDATA/pg_tblspc
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$ oid2name -s
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All tablespaces:
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Oid Tablespace Name
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-------------------------
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1663 pg_default
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1664 pg_global
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155151 fastdisk
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155152 bigdisk
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$ # what databases have objects in tablespace "fastdisk"?
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$ ls -d 155151/*
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155151/17228/ 155151/PG_VERSION
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$ # Oh, what was database 17228 again?
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$ oid2name
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All databases:
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Oid Database Name Tablespace
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----------------------------------
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17228 alvherre pg_default
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17255 regression pg_default
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17227 template0 pg_default
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1 template1 pg_default
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$ # Let's see what objects does this database have in the tablespace.
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$ cd 155151/17228
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$ ls -l
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total 0
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-rw------- 1 postgres postgres 0 sep 13 23:20 155156
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$ # OK, this is a pretty small table ... but which one is it?
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$ oid2name -d alvherre -f 155156
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From database "alvherre":
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Filenode Table Name
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----------------------
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155156 foo
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$ # end of sample session.
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---------------------------------------------------------------------------
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You can also get approximate size data for each object using psql. For
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example,
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SELECT relpages, relfilenode, relname FROM pg_class ORDER BY relpages DESC;
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Each page is typically 8k. Relpages is updated by VACUUM.
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---------------------------------------------------------------------------
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Mail me with any problems or additions you would like to see. Clearing
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house for the code will be at: http://www.crimelabs.net
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b. palmer, bpalmer@crimelabs.net
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