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Diffstat (limited to 'doc/src/sgml/amcheck.sgml')
| -rw-r--r-- | doc/src/sgml/amcheck.sgml | 66 |
1 files changed, 33 insertions, 33 deletions
diff --git a/doc/src/sgml/amcheck.sgml b/doc/src/sgml/amcheck.sgml index dd71dbd679..0dd68f0ba1 100644 --- a/doc/src/sgml/amcheck.sgml +++ b/doc/src/sgml/amcheck.sgml @@ -8,19 +8,19 @@ </indexterm> <para> - The <filename>amcheck</> module provides functions that allow you to + The <filename>amcheck</filename> module provides functions that allow you to verify the logical consistency of the structure of indexes. If the structure appears to be valid, no error is raised. </para> <para> - The functions verify various <emphasis>invariants</> in the + The functions verify various <emphasis>invariants</emphasis> in the structure of the representation of particular indexes. The correctness of the access method functions behind index scans and other important operations relies on these invariants always holding. For example, certain functions verify, among other things, - that all B-Tree pages have items in <quote>logical</> order (e.g., - for B-Tree indexes on <type>text</>, index tuples should be in + that all B-Tree pages have items in <quote>logical</quote> order (e.g., + for B-Tree indexes on <type>text</type>, index tuples should be in collated lexical order). If that particular invariant somehow fails to hold, we can expect binary searches on the affected page to incorrectly guide index scans, resulting in wrong answers to SQL @@ -35,7 +35,7 @@ functions. </para> <para> - <filename>amcheck</> functions may be used only by superusers. + <filename>amcheck</filename> functions may be used only by superusers. </para> <sect2> @@ -82,7 +82,7 @@ ORDER BY c.relpages DESC LIMIT 10; (10 rows) </screen> This example shows a session that performs verification of every - catalog index in the database <quote>test</>. Details of just + catalog index in the database <quote>test</quote>. Details of just the 10 largest indexes verified are displayed. Since no error is raised, all indexes tested appear to be logically consistent. Naturally, this query could easily be changed to call @@ -90,10 +90,10 @@ ORDER BY c.relpages DESC LIMIT 10; database where verification is supported. </para> <para> - <function>bt_index_check</function> acquires an <literal>AccessShareLock</> + <function>bt_index_check</function> acquires an <literal>AccessShareLock</literal> on the target index and the heap relation it belongs to. This lock mode is the same lock mode acquired on relations by simple - <literal>SELECT</> statements. + <literal>SELECT</literal> statements. <function>bt_index_check</function> does not verify invariants that span child/parent relationships, nor does it verify that the target index is consistent with its heap relation. When a @@ -132,13 +132,13 @@ ORDER BY c.relpages DESC LIMIT 10; logical inconsistency or other problem. </para> <para> - A <literal>ShareLock</> is required on the target index by + A <literal>ShareLock</literal> is required on the target index by <function>bt_index_parent_check</function> (a - <literal>ShareLock</> is also acquired on the heap relation). + <literal>ShareLock</literal> is also acquired on the heap relation). These locks prevent concurrent data modification from - <command>INSERT</>, <command>UPDATE</>, and <command>DELETE</> + <command>INSERT</command>, <command>UPDATE</command>, and <command>DELETE</command> commands. The locks also prevent the underlying relation from - being concurrently processed by <command>VACUUM</>, as well as + being concurrently processed by <command>VACUUM</command>, as well as all other utility commands. Note that the function holds locks only while running, not for the entire transaction. </para> @@ -159,13 +159,13 @@ ORDER BY c.relpages DESC LIMIT 10; </sect2> <sect2> - <title>Using <filename>amcheck</> effectively</title> + <title>Using <filename>amcheck</filename> effectively</title> <para> - <filename>amcheck</> can be effective at detecting various types of + <filename>amcheck</filename> can be effective at detecting various types of failure modes that <link linkend="app-initdb-data-checksums"><application>data page - checksums</></link> will always fail to catch. These include: + checksums</application></link> will always fail to catch. These include: <itemizedlist> <listitem> @@ -176,13 +176,13 @@ ORDER BY c.relpages DESC LIMIT 10; <para> This includes issues caused by the comparison rules of operating system collations changing. Comparisons of datums of a collatable - type like <type>text</> must be immutable (just as all + type like <type>text</type> must be immutable (just as all comparisons used for B-Tree index scans must be immutable), which implies that operating system collation rules must never change. Though rare, updates to operating system collation rules can cause these issues. More commonly, an inconsistency in the collation order between a master server and a standby server is - implicated, possibly because the <emphasis>major</> operating + implicated, possibly because the <emphasis>major</emphasis> operating system version in use is inconsistent. Such inconsistencies will generally only arise on standby servers, and so can generally only be detected on standby servers. @@ -190,25 +190,25 @@ ORDER BY c.relpages DESC LIMIT 10; <para> If a problem like this arises, it may not affect each individual index that is ordered using an affected collation, simply because - <emphasis>indexed</> values might happen to have the same + <emphasis>indexed</emphasis> values might happen to have the same absolute ordering regardless of the behavioral inconsistency. See <xref linkend="locale"> and <xref linkend="collation"> for - further details about how <productname>PostgreSQL</> uses + further details about how <productname>PostgreSQL</productname> uses operating system locales and collations. </para> </listitem> <listitem> <para> Corruption caused by hypothetical undiscovered bugs in the - underlying <productname>PostgreSQL</> access method code or sort + underlying <productname>PostgreSQL</productname> access method code or sort code. </para> <para> Automatic verification of the structural integrity of indexes plays a role in the general testing of new or proposed - <productname>PostgreSQL</> features that could plausibly allow a + <productname>PostgreSQL</productname> features that could plausibly allow a logical inconsistency to be introduced. One obvious testing - strategy is to call <filename>amcheck</> functions continuously + strategy is to call <filename>amcheck</filename> functions continuously when running the standard regression tests. See <xref linkend="regress-run"> for details on running the tests. </para> @@ -219,12 +219,12 @@ ORDER BY c.relpages DESC LIMIT 10; simply not be enabled. </para> <para> - Note that <filename>amcheck</> examines a page as represented in some + Note that <filename>amcheck</filename> examines a page as represented in some shared memory buffer at the time of verification if there is only a shared buffer hit when accessing the block. Consequently, - <filename>amcheck</> does not necessarily examine data read from the + <filename>amcheck</filename> does not necessarily examine data read from the file system at the time of verification. Note that when checksums are - enabled, <filename>amcheck</> may raise an error due to a checksum + enabled, <filename>amcheck</filename> may raise an error due to a checksum failure when a corrupt block is read into a buffer. </para> </listitem> @@ -234,7 +234,7 @@ ORDER BY c.relpages DESC LIMIT 10; and operating system. </para> <para> - <productname>PostgreSQL</> does not protect against correctable + <productname>PostgreSQL</productname> does not protect against correctable memory errors and it is assumed you will operate using RAM that uses industry standard Error Correcting Codes (ECC) or better protection. However, ECC memory is typically only immune to @@ -244,7 +244,7 @@ ORDER BY c.relpages DESC LIMIT 10; </para> </listitem> </itemizedlist> - In general, <filename>amcheck</> can only prove the presence of + In general, <filename>amcheck</filename> can only prove the presence of corruption; it cannot prove its absence. </para> @@ -252,19 +252,19 @@ ORDER BY c.relpages DESC LIMIT 10; <sect2> <title>Repairing corruption</title> <para> - No error concerning corruption raised by <filename>amcheck</> should - ever be a false positive. In practice, <filename>amcheck</> is more + No error concerning corruption raised by <filename>amcheck</filename> should + ever be a false positive. In practice, <filename>amcheck</filename> is more likely to find software bugs than problems with hardware. - <filename>amcheck</> raises errors in the event of conditions that, + <filename>amcheck</filename> raises errors in the event of conditions that, by definition, should never happen, and so careful analysis of - <filename>amcheck</> errors is often required. + <filename>amcheck</filename> errors is often required. </para> <para> There is no general method of repairing problems that - <filename>amcheck</> detects. An explanation for the root cause of + <filename>amcheck</filename> detects. An explanation for the root cause of an invariant violation should be sought. <xref linkend="pageinspect"> may play a useful role in diagnosing - corruption that <filename>amcheck</> detects. A <command>REINDEX</> + corruption that <filename>amcheck</filename> detects. A <command>REINDEX</command> may not be effective in repairing corruption. </para> |