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pg_check

An extension that provides basic consistency checking functionality for tables and b-tree indexes. Currently this performs basic checks at the page and item level, for example:

  • page header features (lower <= upper <= special etc.)
  • items not overlapping
  • attributes not overflowing the tuple end
  • invalid varlena sizes (negative or over 1GB, ...)

Moreover it's possible to cross-check the table and indexes, i.e. to check if there are any missing / superfluous items in the index (compared to the heap).

This extension does not implement correcting any of the issues, nor it fully checks the index structure (except for the generic page checks mentioned above). The extension does not support index types other than b-tree (yet).

Installation

This is a regular extension (9.1) or a contrib module (9.0), so it may be installed rather easily - do either this

$ make install
$ psql dbname -c "CREATE EXTENSION pg_check"

or this (on 9.0)

$ make install
$ psql dbname < `pg_config --sharedir`/contrib/pg_check--0.1.0.sql

and the extension should be installed.

Functions

Currently there are four functions available

  • pg_check_table(name, blk_from, blk_to) - checks range of blocks of the heap table
  • pg_check_table(name, checkIndexes, crossCheck) - checks the table with the options to check all indexes on it, and even cross-checking the indexes with the table
  • pg_check_index(name, blk_from, blk_to) - checks range of blocks for the index
  • pg_check_index(name) - checks a single index

So if you want to check table "my_table" and all the indexes on it, do this:

db=# SELECT pg_check_table('my_table', true, true);

and it will print out info about the checks (and return number of issues).

Be very careful about running the pg_check_table with crossCheck=true because that means a more restrictive lock mode (SHARE ROW EXCLUSIVE) is needed instead of the ACCESS SHARE lock used with crossCheck=false.

So use cross-checking wisely, as it prevents any modification of the data (table or indexes). This may even cause deadlocks, if another process acquires the locks in different order (index before table). The lock on the table is held the whole time, the locks on the indexes are acquired only when checking the indexes (so there's always at most one index locked).

GUC options

The extension (once loaded) uses these two options:

  • pg_check.debug = {true | false}
  • pg_check.bitmap_format = {binary, base64, hex, none}

The first one allows you to enable debug output when cross-checking the table and indexes - by default it's set to false and by setting it to true the extension will print details about the bitmaps.

The bimap may be printed in several formats - "binary" (as a sequence of 0s and 1s), "hex" (hexa-decimal) or "base64" (the usual base64 encoding). Or it may be disabled by "none" (thus only basic info about the bitmap will be printed). By default the format is "binary".

This is intended for debugging purposes only, the amount of information printed may be significant (even megabytes).

Messages

The functions may print various info about the blocks/tuples, depending on the client_min_messages level.

  • WARNING - only info about actual issues
  • DEBUG1 - info about pages
  • DEBUG2 - info about tuples on a page
  • DEBUG3 - info about attributes of a tuple

License

This software is provided under the BSD license. See LICENSE for details.