+ class="PARAMETER">name IN SHARE MODE
+ statement will wait until any concurrent holders of ROW
+ EXCLUSIVE mode locks commit or roll back. Thus, once you
+ obtain the lock, there are no uncommitted writes outstanding;
+ furthermore none can begin until you release the lock.
-
+
- If a transaction of this sort is going to
- change the data in the table, then it should use SHARE ROW EXCLUSIVE lock
- mode instead of SHARE mode. This ensures that only one transaction of
- this type runs at a time. Without this, a deadlock is possible: two
- transactions might both acquire SHARE mode, and then be unable to also
- acquire ROW EXCLUSIVE mode to actually perform their updates. (Note that
- a transaction's own locks never conflict, so a transaction can acquire
- ROW EXCLUSIVE mode when it holds SHARE mode --- but not if anyone else
- holds SHARE mode.)
+ To achieve a similar effect when running a transaction at the
+ isolation level serializable, you have to execute the LOCK
+ TABLE statement before executing any data modification
+ statement. A serializable transaction's view of data will be
+ frozen when its first data modification statement begins. A later
+ LOCK TABLE will still prevent concurrent writes --- but it
+ won't ensure that what the transaction reads corresponds to the
+ latest committed values.
- Two general rules may be followed to prevent deadlock conditions:
+ If a transaction of this sort is going to change the data in the
+ table, then it should use SHARE ROW EXCLUSIVE lock mode
+ instead of SHARE mode. This ensures that only one
+ transaction of this type runs at a time. Without this, a deadlock
+ is possible: two transactions might both acquire SHARE
+ mode, and then be unable to also acquire ROW EXCLUSIVE
+ mode to actually perform their updates. (Note that a transaction's
+ own locks never conflict, so a transaction can acquire ROW
+ EXCLUSIVE mode when it holds SHARE mode --- but not
+ if anyone else holds SHARE mode.) To avoid deadlocks,
+ make sure all transactions acquire locks on the same objects in the
+ same order, and if multiple lock modes are involved for a single
+ object, then transactions should always acquire the most
+ restrictive mode first.
-
-
- Transactions have to acquire locks on the same objects in the same order.
-
-
- For example, if one application updates row R1 and than updates
- row R2 (in the same transaction) then the second application shouldn't
- update row R2 if it's going to update row R1 later (in a single transaction).
- Instead, it should update rows R1 and R2 in the same order as the first
- application.
-
-
-
-
- If multiple lock modes are involved for a single object,
- then transactions should always acquire the most restrictive mode first.
-
-
- An example for this rule was given previously when discussing the
- use of SHARE ROW EXCLUSIVE mode rather than SHARE mode.
-
-
-
-
-
-
PostgreSQL does detect deadlocks and will
- rollback at least one waiting transaction to resolve the deadlock.
- If it is not practical to code an application to follow the above rules
- strictly, an alternative solution is to be prepared to retry transactions
- when they are aborted by deadlocks.
+ More information about the lock modes and locking strategies can be
+ found in .
+
- When locking multiple tables, the command LOCK a, b; is
- equivalent to LOCK a; LOCK b;. The tables are locked one-by-one
- in the order specified in the
- LOCK command.
-
+
+
Parameters
+
+
+
+ name
+
+ The name (optionally schema-qualified) of an existing table to
+ lock.
+
+
+ The command LOCK a, b; is equivalent to
+ LOCK a; LOCK b;. The tables are locked one-by-one in
+ the order specified in the LOCK command.
+
+
+
+
+
+ lockmode
+
+ The lock mode specifies which locks this lock conflicts with.
+ Lock modes are described in .
+
+
+ If no lock mode is specified, then ACCESS
+ EXCLUSIVE, the most restrictive mode, is used.
+
+
+
+
+
-
-
- 1999-06-08
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
+
+
Diagnostics
+
+
+
+ LOCK TABLE
+
+ Message returned if the lock was successfully acquired.
+
+
+
+
+
+
+
+
Notes
LOCK ... IN ACCESS SHARE MODE requires SELECT
LOCK is useful only inside a transaction block
- (BEGIN...COMMIT), since the lock is dropped
+ (BEGIN/COMMIT pair), since the lock is dropped
as soon as the transaction ends. A LOCK command appearing
outside any transaction block forms a self-contained transaction, so the
lock will be dropped as soon as it is obtained.
-
RDBMS locking uses the following standard terminology:
-
-
-
- EXCLUSIVE
-
- An exclusive lock prevents other locks of the same type from being
- granted.
-
-
-
-
-
- SHARE
-
- A shared lock allows others to also hold the same type of lock,
- but prevents the corresponding EXCLUSIVE lock from being granted.
-
-
-
-
-
- ACCESS
-
- Locks table schema.
-
-
-
-
-
- ROW
-
- Locks individual rows.
-
-
-
-
+ LOCK TABLE only deals with table-level locks, and so
+ the mode names involving ROW are all misnomers. These
+ mode names should generally be read as indicating the intention of
+ the user to acquire row-level locks within the locked table. Also,
+ ROW EXCLUSIVE mode is a sharable table lock. Keep in
+ mind that all the lock modes have identical semantics so far as
+ LOCK TABLE is concerned, differing only in the rules
+ about which modes conflict with which.
-
-
PostgreSQL does not follow this terminology
- exactly. LOCK TABLE only deals with table-level locks, and
- so the mode names involving ROW are all misnomers. These mode names
- should generally be read as indicating the intention of the user to
- acquire row-level locks within the locked table. Also,
- ROW EXCLUSIVE mode does not follow this naming convention accurately,
- since it is a sharable table lock. Keep in mind that all the lock modes
- have identical semantics so far as LOCK TABLE is concerned,
- differing only in the rules about which modes conflict with which.
-
-
-
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Examples
- Obtain a SHARE lock on a primary key table when going to perform
+ Obtain a SHARE lock on a primary key table when going to perform
inserts into a foreign key table:
BEGIN WORK;
LOCK TABLE films IN SHARE MODE;
SELECT id FROM films
INSERT INTO films_user_comments VALUES
(_id_, 'GREAT! I was waiting for it for so long!');
COMMIT WORK;
-
+
- Take a SHARE ROW EXCLUSIVE lock on a primary key table when going to perform
+ Take a SHARE ROW EXCLUSIVE lock on a primary key table when going to perform
a delete operation:
BEGIN WORK;
LOCK TABLE films IN SHARE ROW EXCLUSIVE MODE;
DELETE FROM films_user_comments WHERE id IN
(SELECT id FROM films WHERE rating < 5);
DELETE FROM films WHERE rating < 5;
COMMIT WORK;
-
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
+
+
Compatibility
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no
LOCK TABLE in
SQL92,
- which instead uses SET TRANSACTION to specify
- concurrency levels on transactions. We support that too; see
- for details.
-
+ There is no LOCK TABLE in the SQL standard,
+ which instead uses SET TRANSACTION to specify
+ concurrency levels on transactions. PostgreSQL supports that too;
+ see
+ endterm="SQL-SET-TRANSACTION-TITLE"> for details.
+
- Except for ACCESS SHARE, ACCESS EXCLUSIVE, and SHARE UPDATE EXCLUSIVE lock
-
modes, the PostgreSQL lock modes and the
- LOCK TABLE syntax are compatible with those
-
- refsect2>
+ Except for ACCESS SHARE, ACCESS EXCLUSIVE,
+ and SHARE UPDATE EXCLUSIVE lock modes, the
+
PostgreSQL lock modes and the
+ LOCK TABLE syntax are compatible with those
+ para>
NOTIFY
SQL - Language Statements
+
-
- NOTIFY
-
-
- generate a notification
-
+ NOTIFY
+ generate a notification
+
-
- 1999-07-20
-
-
+
NOTIFY name
-
-
-
-
- 1998-10-07
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- notifyname
-
- Notify condition to be signaled.
-
-
-
-
-
-
-
-
-
- 1998-10-07
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-NOTIFY
-
-
- Acknowledgement that notify command has executed.
-
-
-
-
- Notify events
-
- Events are delivered to listening frontends; whether and how each frontend
- application reacts depends on its programming.
-
-
-
-
-
-
+
-
-
- 1998-10-07
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
+
- The NOTIFY command sends a notify event to each
- frontend application that has previously executed
- LISTEN notifyname
- for the specified notify condition in the current database.
+ The NOTIFY command sends a notification event to each
+ client application that has previously executed
+ LISTEN name
+ for the specified notification name in the current database.
+
- The information passed to the frontend for a notify event includes the notify
-
condition name and the notifying backend process's
PID. It is up to the- database designer to define the condition names that will be used in a given
+ The information passed to the client for a notifiation event includes the notification
+
name and the notifying session's server process
PID. It is up to the+ database designer to define the notification names that will be used in a given
database and what each one means.
+
- Commonly, the notify condition name is the same as the name of some table in
- the database, and the notify event essentially means I changed this table,
+ Commonly, the notification name is the same as the name of some table in
+ the database, and the notify event essentially means, I changed this table,
take a look at it to see what's new. But no such association is enforced by
the NOTIFY and LISTEN commands. For
- example, a database designer could use several different condition names
+ example, a database designer could use several different notification names
to signal different sorts of changes to a single table.
+
NOTIFY provides a simple form of signal or
-
IPC (interprocess communication) mechanism for a collection of processes
+ interprocess communication mechanism for a collection of processes
accessing the same
PostgreSQL database.
Higher-level mechanisms can be built by using tables in the database to
- pass additional data (beyond a mere condition name) from notifier to
+ pass additional data (beyond a mere notification name) from notifier to
listener(s).
+
When NOTIFY is used to signal the occurrence of changes
to a particular table, a useful programming technique is to put the
In this way, notification happens automatically when the table is changed,
and the application programmer can't accidentally forget to do it.
+
NOTIFY interacts with SQL transactions in some important
ways. Firstly, if a NOTIFY is executed inside a
transaction, the notify events are not delivered until and unless the
transaction is committed. This is appropriate, since if the transaction
- is aborted we would like all the commands within it to have had no
+ is aborted, all the commands within it have had no
effect, including NOTIFY. But it can be disconcerting if one
- is expecting the notify events to be delivered immediately. Secondly, if
- a listening backend receives a notify signal while it is within a transaction,
- the notify event will not be delivered to its connected frontend until just
+ is expecting the notification events to be delivered immediately. Secondly, if
+ a listening session receives a notification signal while it is within a transaction,
+ the notification event will not be delivered to its connected client until just
after the transaction is completed (either committed or aborted). Again, the
- reasoning is that if a notify were delivered within a transaction that was
+ reasoning is that if a notification were delivered within a transaction that was
later aborted, one would want the notification to be undone somehow---but
- the backend cannot take back
a notify once it has sent it to the frontend.
- So notify events are only delivered between transactions. The upshot of this
+ the server cannot take back
a notification once it has sent it to the client.
+ So notification events are only delivered between transactions. The upshot of this
is that applications using NOTIFY for real-time signaling
should try to keep their transactions short.
+
NOTIFY behaves like Unix signals in one important
- respect: if the same condition name is signaled multiple times in quick
- succession, recipients may get only one notify event for several executions
+ respect: if the same notification name is signaled multiple times in quick
+ succession, recipients may get only one notification event for several executions
of NOTIFY. So it is a bad idea to depend on the number
- of notifies received. Instead, use NOTIFY to wake up
+ of notifications received. Instead, use NOTIFY to wake up
applications that need to pay attention to something, and use a database
object (such as a sequence) to keep track of what happened or how many times
it happened.
+
- It is common for a frontend that sends NOTIFY to be
- listening on the same notify name itself. In that case it will get back a
- notify event, just like all the other listening frontends. Depending on the
- application logic, this could result in useless work---for example,
- re-reading a database table to find the same updates that that frontend just
- wrote out. In
PostgreSQL 6.4 and later, it is
- possible to avoid such extra work by noticing whether the notifying backend
- process's
PID (supplied in the notify event message) is the same as one's own- backend's
PID (available from libpq). When they are the same, the notify- event is one's own work bouncing back, and can be ignored. (Despite what was
- said in the preceding paragraph, this is a safe technique.
-
PostgreSQL keeps self-notifies separate from notifies
- arriving from other backends, so you cannot miss an outside notify by ignoring
- your own notifies.)
+ It is common for a client that executes NOTIFY
+ to be listening on the same notification name itself. In that case
+ it will get back a notification event, just like all the other
+ listening sessions. Depending on the application logic, this could
+ result in useless work, for example, reading a database table to
+ find the same updates that that session just wrote out. It is
+ possible to avoid such extra work by noticing whether the notifying
+ session's server process
PID (supplied in the+ notification event message) is the same as one's own session's
+
PID (available from libpq). When they+ are the same, the notification event is one's own work bouncing
+ back, and can be ignored. (Despite what was said in the preceding
+ paragraph, this is a safe technique.
+
PostgreSQL keeps self-notifiications
+ separate from notifications arriving from other sessions, so you
+ cannot miss an outside notification by ignoring your own
+ notifications.)
+
+
+
+
Parameters
+
+
+
+ name
+
+ Name of the notification to be signaled (any identifier).
+
+
+
+
+
+
+
+
Diagnostics
-
-
- 1998-10-07
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
- name
- can be any string valid as a name;
- it need not correspond to the name of any actual table. If
- name
- is enclosed in double-quotes, it need not even be a syntactically
- valid name, but can be any string up to 63 characters long.
-
- In some previous releases of
- name
- had to be enclosed in double-quotes when it did not correspond to any existing
- table name, even if syntactically valid as a name. That is no longer required.
-
- In
PostgreSQL releases prior to 6.4, the backend
-
PID delivered in a notify message was always the PID of the frontend's own- backend. So it was not possible to distinguish one's own notifies from other
- clients' notifies in those earlier releases.
-
-
+
+
+ NOTIFY
+
+ Message returned when the commmand has executed.
+
+
+
+
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Examples
+
Configure and execute a listen/notify sequence from
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no NOTIFY statement in
-
-
+
+
Compatibility
+
+ There is no NOTIFY statement in the SQL
+ standard.
+
PREPARE
SQL - Language Statements
+
-
- PREPARE
-
-
- create a prepared query
-
+ PREPARE
+ prepare a statement for execution
+
-
- 2002-08-12
-
-
- PREPARE plan_name [ (datatype [, ...] ) ] AS query
-
-
-
-
- 2002-08-12
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- plan_name
-
- An arbitrary name given to this particular prepared query. It
- must be unique within a single session, and is used to execute
- or remove a previously prepared query.
-
-
-
-
- datatype
-
- The data-type of a parameter to the prepared query.
- To refer to the parameters in the prepared query itself,
- use $1, $2, etc.
-
-
-
-
- query
-
- Any SELECT, INSERT, UPDATE,
- or DELETE query.
-
-
-
-
-
-
-
-
-
- 2002-08-12
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
- PREPARE
-
-
- The query has been prepared successfully.
-
-
-
-
-
-
-
+
+PREPARE plan_name [ (datatype [, ...] ) ] AS statement
+
-
-
- 2002-08-12
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
+
- PREPARE creates a prepared query. A prepared
- query is a server-side object that can be used to optimize
+ PREPARE creates a prepared statement. A prepared
+ statement is a server-side object that can be used to optimize
performance. When the PREPARE statement is
- executed, the specified query is parsed, rewritten, and
- planned. When a subsequent EXECUTE statement is
- issued, the prepared query need only be executed. Thus, the
+ executed, the specified statement is parsed, rewritten, and
+ planned. When an EXECUTE command is subsequently
+ issued, the prepared statement need only be executed. Thus, the
parsing, rewriting, and planning stages are only performed once,
- instead of every time the query is executed.
+ instead of every time the statement is executed.
- Prepared queries can take parameters: values that are
- substituted into the query when it is executed. To specify the
- parameters to a prepared query, include a list of data-types with
- the PREPARE statement. In the query itself, you
- can refer to the parameters by position using
+ Prepared statements can take parameters: values that are
+ substituted into the statement when it is executed. To include
+ parameters in a prepared statement, supply a list of data types in
+ the PREPARE statement, and, in the statement to
+ be prepared itself, refer to the parameters by position using
$1, $2, etc. When executing
- the query, specify the actual values for these parameters in the
-
EXECUTE statement -- refer to
- linkend="sql-execute" endterm="sql-execute-title">
- for more information.
+ the statement, specify the actual values for these parameters in
+
the EXECUTE statement. Refer to
+ linkend="sql-execute" endterm="sql-execute-title"> for more
+ information about that.
- Prepared queries are stored locally (in the current backend), and
- only exist for the duration of the current database session. When
- the client exits, the prepared query is forgotten, and so it must be
- re-created before being used again. This also means that a single
- prepared query cannot be used by multiple simultaneous database
- clients; however, each client can create their own prepared query
+ Prepared statements are only stored in and for the duration of
+ the current database session. When
+ the session ends, the prepared statement is forgotten, and so it must be
+ recreated before being used again. This also means that a single
+ prepared statement cannot be used by multiple simultaneous database
+ clients; however, each client can create their own prepared statement
to use.
- Prepared queries have the largest performance advantage when a
- single backend is being used to execute a large number of similar
- queries. The performance difference will be particularly
- significant if the queries are complex to plan or rewrite. For
+ Prepared statements have the largest performance advantage when a
+ single session is being used to execute a large number of similar
+ statements. The performance difference will be particularly
+ significant if the statements are complex to plan or rewrite, for
example, if the query involves a join of many tables or requires
- the application of several rules. If the query is relatively simple
+ the application of several rules. If the statement is relatively simple
to plan and rewrite but relatively expensive to execute, the
- performance advantage of prepared queries will be less noticeable.
+ performance advantage of prepared statements will be less noticeable.
+
-
-
- 2002-08-12
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
-
- In some situations, the query plan produced by
-
PostgreSQL for a prepared query may be
- inferior to the plan produced if the query were submitted and
- executed normally. This is because when the query is planned (and
- the optimizer attempts to determine the optimal query plan), the
- actual values of any parameters specified in the query are
- unavailable.
PostgreSQL collects
- statistics on the distribution of data in the table, and can use
- constant values in a query to make guesses about the likely
- result of executing the query. Since this data is unavailable when
- planning prepared queries with parameters, the chosen plan may be
- sub-optimal. To examine the query plan
-
PostgreSQL has chosen for a prepared
- query, use EXPLAIN EXECUTE.
-
-
- For more information on query planning and the statistics
- collected by
PostgreSQL for query
- optimization purposes, see the
- endterm="sql-analyze-title"> documentation.
-
-
+
+
Parameters
+
+
+
+ plan_name
+
+ An arbitrary name given to this particular prepared
+ statement. It must be unique within a single session and is
+ subsequently used to execute or deallocate a previously prepared
+ statement.
+
+
+
+
+
+ datatype
+
+ The data type of a parameter to the prepared statement. To
+ refer to the parameters in the prepared statement itself, use
+ $1, $2, etc.
+
+
+
+
+
+ statement
+
+ Any SELECT, INSERT, UPDATE,
+ or DELETE statement.
+
+
+
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 2002-08-12
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- SQL92 includes a PREPARE statement, but it is
- only for use in embedded SQL clients. The
- PREPARE statement implemented by
-
PostgreSQL also uses a somewhat
- different syntax.
-
-
+
+
Diagnostics
+
+
+
+ PREPARE
+
+ Message returned if the statement has been prepared successfully.
+
+
+
+
+
+
+
+
Notes
+
+ In some situations, the query plan produced by for a prepared
+ statement may be inferior to the plan produced if the statement
+ were submitted and executed normally. This is because when the
+ statement is planned and the planer attempts to determine the
+ optimal query plan, the actual values of any parameters specified
+ in the statement are
+ unavailable.
PostgreSQL collects
+ statistics on the distribution of data in the table, and can use
+ constant values in a statement to make guesses about the likely
+ result of executing the statement. Since this data is unavailable
+ when planning prepared statements with parameters, the chosen plan
+ may be suboptimal. To examine the query plan
+
PostgreSQL has chosen for a prepared
+ statement, use EXPLAIN EXECUTE.
+
+
+ For more information on query planning and the statistics collected
+ by
PostgreSQL for that purpose, see
+ the
+ documentation.
+
+
+
+
+
Compatibility
+
+ The SQL standard includes a PREPARE statement,
+ but it is only for use in embedded SQL. This version of the
+ PREPARE statement also uses a somewhat different
+ syntax.
+
REINDEX
SQL - Language Statements
+
-
- REINDEX
-
-
- rebuild corrupted indexes
-
+ REINDEX
+ rebuild indexes
+
-
- 2000-03-30
-
-
+
REINDEX { DATABASE | TABLE | INDEX } name [ FORCE ]
-
-
-
-
- 2000-03-30
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- DATABASE
-
- Recreate all system indexes of a specified database. Indexes on
- user tables are not included. This form of REINDEX can
- only be used in standalone mode (see below).
-
-
-
-
- TABLE
-
- Recreate all indexes of a specified table.
-
-
-
-
- INDEX
-
- Recreate a specified index.
-
-
-
-
- name
-
- The name of the specific database/table/index to be reindexed.
- Table and index names may be schema-qualified.
-
-
-
-
- FORCE
-
- Force rebuild of system indexes. Without this keyword
- REINDEX skips system indexes that are not marked invalid.
- FORCE is irrelevant for REINDEX INDEX, or when reindexing
- user indexes.
-
-
-
-
-
-
-
-
-
- 2000-03-30
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-REINDEX
-
-
- Message returned if the table is successfully reindexed.
-
-
-
-
-
-
+
-
-
- 2000-03-30
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
+
REINDEX rebuilds an index based on the data
stored in the table, replacing the old copy of the index. There are
two main reasons to use REINDEX:
- <orderedlist>
+ <itemizedlist>
An index has become corrupted, and no longer contains valid
- data. Although in theory this should never be necessary, in
+ data. Although in theory this should never happen, in
practice indexes may become corrupted due to software bugs or
hardware failures. REINDEX provides a
recovery method.
The index in question contains a lot of dead index pages that
- are not being reclaimed. This can occur with B+-tree indexes
+ are not being reclaimed. This can occur with B-tree indexes in PostgreSQL
under certain access patterns. REINDEX
provides a way to reduce the space consumption of the index by
writing a new version of the index without the dead pages. See
- for more information. The rest of this reference page
- mostly discusses how to use REINDEX to
- recover from index corruption.
+ for more information.
- orderedlist>
+ itemizedlist>
- If you suspect corruption of an index on a user table, you can
- simply rebuild that index, or all indexes on the table, using
- REINDEX INDEX or REINDEX TABLE.
+ If you suspect corruption of an index on a user table, you can
+ simply rebuild that index, or all indexes on the table, using
+ REINDEX INDEX or REINDEX
+ TABLE. Another approach to dealing with a corrupted
+ user-table index is just to drop and recreate it. This may in fact
+ be preferable if you would like to maintain some semblance of
+ normal operation on the table meanwhile. REINDEX
+ acquires exclusive lock on the table, while CREATE
+ INDEX only locks out writes not reads of the table.
-
- Another approach to dealing with a corrupted user-table index is
- just to drop and recreate it. This may in fact be preferable if
- you would like to maintain some semblance of normal operation on
- the table meanwhile. REINDEX acquires exclusive lock
- on the table, while CREATE INDEX only locks out writes
- not reads of the table.
-
-
-
- Things are more difficult if you need to recover from corruption of an
- index on a system table. In this case it's important for the backend
- doing the recovery to not have used any of the suspect indexes itself.
- (Indeed, in this sort of scenario you may find that backends are
- crashing immediately at start-up, due to reliance on the corrupted
- indexes.) To recover safely, the postmaster must be shut down and a
- stand-alone
PostgreSQL backend must be
- started instead, giving it
- the command-line options -O and -P (these options allow system table
- modifications and prevent use of system indexes, respectively). Then
- issue REINDEX DATABASE, REINDEX TABLE,
- REINDEX INDEX, or depending on how much you want to reconstruct.
- If in doubt, use REINDEX DATABASE FORCE to force reconstruction
- of all system indexes in the database. Then quit the standalone backend
- and restart the postmaster.
+ Things are more difficult if you need to recover from corruption of
+ an index on a system table. In this case it's important for the
+ system to not have used any of the suspect indexes itself.
+ (Indeed, in this sort of scenario you may find that server
+ processes are crashing immediately at start-up, due to reliance on
+ the corrupted indexes.) To recover safely, the server must be shut
+ down and a stand-alone
PostgreSQL server
+ must be started instead with the command-line options
+ and . (These options allow
+ system table modifications and prevent use of system indexes,
+ respectively.) Then, REINDEX DATABASE,
+ REINDEX TABLE, or REINDEX INDEX can be
+ issued, depending on how much you want to reconstruct. If in
+ doubt, use REINDEX DATABASE FORCE to force
+ reconstruction of all system indexes in the database. Then quit
+ the standalone server session and restart the real server.
- Since this is likely the only situation when most people will ever use
- a standalone backend, some usage notes might be in order:
+ See the reference page for more
+ information about how to interact with the stand-alone server
+ interface.
+
+
+
+
+
Parameters
-
+
+
+ DATABASE
- Start the backend with a command like
-
-postgres -D $PGDATA -O -P my_database
-
- Provide the correct path to the database area with
- make sure that the environment variable PGDATA is set.
- Also specify the name of the particular database you want to work in.
+ Recreate all system indexes of a specified database. Indexes on
+ user tables are not included. This form of REINDEX
+ can only be used in stand-alone mode (see above).
+
+
+ TABLE
- You can issue any SQL command, not only REINDEX.
+ Recreate all indexes of a specified table.
+
+
+ INDEX
- Be aware that the standalone backend treats newline as the command
- entry terminator; there is no intelligence about semicolons,
- as there is in
psql. To continue a command- across multiple lines, you must type backslash just before each
- newline except the last one.
- Also, you won't have any of the conveniences of command-line editing
- (no command history, for example).
+ Recreate a specified index.
+
+
+ name
- T
o quit the backend, type EOF (- action="simul">ControlD, usually).
+ The name of the specific database, table, or index to be
+ reindexed. Table and index names may be schema-qualified.
+
-
+
+ FORCE
+
+ Force rebuild of system indexes. Without this key word,
+ REINDEX skips system indexes that are not marked
+ invalid. FORCE is irrelevant for REINDEX
+ INDEX or when reindexing user indexes.
+
+
+
+
+
+
+
+
Diagnostics
- See the reference page for more information.
-
+
+
+ REINDEX
+
+ Message returned if the indexes were successfully recreated.
+
+
+
+
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Examples
+
- Recreate the indexes on the table mytable:
+ Recreate the indexes on the table my_table:
- REINDEX TABLE mytable;
-
+REINDEX TABLE my_table;
+
Rebuild a single index:
- REINDEX INDEX my_index;
-
+REINDEX INDEX my_index;
+
- Rebuild all system indexes (this will only work in a standalone backend):
+ Rebuild all system indexes (this will only work in a stand-alone
+ server session):
- REINDEX DATABASE my_database FORCE;
-
+REINDEX DATABASE my_database FORCE;
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 2000-03-30
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no
REINDEX in
SQL92.
-
-
+
+
Compatibility
+
+ There is no REINDEX command in the SQL standard.
+
Description
- REVOKE allows the creator of an object to revoke
- previously granted permissions from one or more users or groups of users.
- The key word PUBLIC refers to the implicitly defined
- group of all users.
+ The REVOKE command revokes previously granted
+ privileges from one or more users or groups of users. The key word
+ PUBLIC refers to the implicitly defined group of
+ all users.
Note that any particular user will have the sum
of privileges granted directly to him, privileges granted to any group he
is presently a member of, and privileges granted to
- PUBLIC. Thus, for example, revoking SELECT privilege
+ PUBLIC. Thus, for example, revoking SELECT privilege
from PUBLIC does not necessarily mean that all users
- have lost SELECT privilege on the object: those who have it granted
+ have lost SELECT privilege on the object: those who have it granted
directly or via a group will still have it.
Compatibility
-
-
SQL92
-
The compatibility notes of the command
apply analogously to REVOKE. The syntax summary is:
-REVOKE [ GRANT OPTION FOR ] { SELECT | INSERT | UPDATE | DELETE | REFERENCES }
+REVOKE [ GRANT OPTION FOR ] privileges
ON object [ ( column [, ...] ) ]
FROM { PUBLIC | username [, ...] }
{ RESTRICT | CASCADE }
One of RESTRICT or CASCADE
is required.
-
ROLLBACK
SQL - Language Statements
+
-
- ROLLBACK
-
-
- abort the current transaction
-
+ ROLLBACK
+ abort the current transaction
+
-
- 1999-07-20
-
-
+
ROLLBACK [ WORK | TRANSACTION ]
-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
- None.
-
-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-ROLLBACK
-
-
- Message returned if successful.
-
-
-
-
-
-
-WARNING: ROLLBACK: no transaction in progress
-
-
- If there is not any transaction currently in progress.
-
-
-
-
-
-
+
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
ROLLBACK rolls back the current transaction and causes
all the updates made by the transaction to be discarded.
+
+
+
+
Parameters
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
- Use
- to successfully terminate a transaction.
- is a
- synonym for ROLLBACK.
-
-
+
+
+ WORK
+ TRANSACTION
+
+ Optional key words. They have no effect.
+
+
+
+
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Diagnostics
+
+
+
+ ROLLBACK
+
+ Message returned if successful.
+
+
+
+
+
+ WARNING: ROLLBACK: no transaction in progress
+
+ If there is not any transaction currently in progress.
+
+
+
+
+
+
+
+
Notes
+
- To abort all changes:
+ Use to
+ successfully terminate a transaction.
+
+
-ROLLBACK WORK;
-
+
+
Examples
+
+ To abort all changes:
+ROLLBACK;
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
+
+
Compatibility
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
-
SQL92 only specifies the two forms
ROLLBACK- and ROLLBACK WORK. Otherwise full compatibility.
-
-
+ The SQL standard only specifies the two forms
+ ROLLBACK and ROLLBACK
+ WORK. Otherwise, this command is fully conforming.
+
-
- 2002-07-26
-
-
START TRANSACTION
SQL - Language Statements
-
+
START TRANSACTION [ ISOLATION LEVEL { READ COMMITTED | SERIALIZABLE } ] [ READ WRITE | READ ONLY ]
-
-
-
-
- 1998-09-27
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
- None.
-
-
-
-
-
- 1998-09-27
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-
-START TRANSACTION
-
-
- Message returned if successful.
-
-
-
-
-
-WARNING: BEGIN: already a transaction in progress
-
-
- If there is already a transaction in progress when the
- command is issued.
-
-
-
-
-
-
+
respects, the behavior of this command is identical to the
linkend="sql-begin" endterm="sql-begin-title"> command.
+
+
+
+
Parameters
+ See under
+ endterm="sql-set-transaction-title"> about the meaning of the
+ parameters.
+
+
+
+
+
Diagnostics
+
+
+
+ START TRANSACTION
+
+ Message returned if successful.
+
+
+
+
+
+ WARNING: BEGIN: already a transaction in progress
+
+ Message returned if there was already a transaction in progress
+ when the command was issued.
+
+
+
+
- id="R1-SQL-START-TRANSACTION-3">
+
Compatibility
- SQL99; but see also the compatibility section of
- linkend="sql-set-transaction" endterm="sql-set-transaction-title">.
+ This command conforms to the SQL standard; but see also the
+ compatibility section of
+ endterm="sql-set-transaction-title">.
TRUNCATE
SQL - Language Statements
+
-
- TRUNCATE
-
-
- empty a table
-
+ TRUNCATE
+ empty a table
+
-
- 1999-07-20
-
-
+
TRUNCATE [ TABLE ] name
-
-
-
-
- 1998-09-08
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- name
-
- The name (optionally schema-qualified) of the table to be truncated.
-
-
-
-
-
-
-
-
-
- 1998-09-08
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-TRUNCATE TABLE
-
-
- Message returned if the table is successfully truncated.
-
-
-
-
-
-
+
-
-
- 1998-09-08
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
+
TRUNCATE quickly removes all rows from a
table. It has the same effect as an unqualified
table it is faster. This is most useful on large tables.
+
+
+
Parameter
+
+
+
+ name
+
+ The name (optionally schema-qualified) of the table to be truncated.
+
+
+
+
+
+
+
+
Diagnostics
+
+
+
+ TRUNCATE TABLE
+
+ Message returned if the table was successfully truncated.
+
+
+
+
+
+
+
+
Examples
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
Truncate the table bigtable:
TRUNCATE TABLE bigtable;
-
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 1998-09-08
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no
TRUNCATE in
SQL92.
-
-
+
+
Compatibility
+
+ There is no TRUNCATE command in the SQL standard.
+
UNLISTEN
SQL - Language Statements
+
-
- UNLISTEN
-
-
- stop listening for a notification
-
+ UNLISTEN
+ stop listening for a notification
+
-
- 1998-10-19
-
-
-UNLISTEN { notifyname | * }
-
-
-
-
- 1998-10-19
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- notifyname
-
- Name of previously registered notify condition.
-
-
-
-
- *
-
- All current listen registrations for this backend are cleared.
-
-
-
-
-
-
-
-
-
- 1998-10-19
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-UNLISTEN
-
-
- Acknowledgment that statement has executed.
-
-
-
-
-
-
+
+UNLISTEN { name | * }
+
-
-
- 1998-10-19
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
- UNLISTEN
- is used to remove an existing NOTIFY registration.
- UNLISTEN cancels any existing registration of the current
-
PostgreSQL session as a listener on the notify
- condition notifyname.
- The special condition wildcard * cancels all listener registrations
- for the current session.
+ UNLISTEN is used to remove an existing
+ registration for NOTIFY events.
+ UNLISTEN cancels any existing registration of
+ the current
PostgreSQL session as a
+ listener on the notification
+ class="PARAMETER">name. The special wildcard
+ * cancels all listener registrations for the
+ current session.
discussion of the use of LISTEN and
NOTIFY.
+
+
+
+
Parameters
+
+
+
+ name
+
+ Name of a notification (any identifier).
+
+
+
+
+
+ *
+
+ All current listen registrations for this session are cleared.
+
+
+
+
+
+
+
+
Diagnostics
+
+
+
+ UNLISTEN
+
+ Message returned when the command has executed.
+
+
+
+
+
+
+
+
Notes
+
+ You unlisten something you were not listening for; no warning or error will appear.
+
-
-
- 1998-10-19
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
- notifyname
- need not be a valid class name but can be any string valid
- as a name up to 64 characters long.
-
- The backend does not complain if you unlisten something you were not
- listening for.
- Each backend will automatically execute UNLISTEN * when
- exiting.
-
-
+ At the end of each session, UNLISTEN * ist
+ automatically executed.
+
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Examples
- To subscribe to an existing registration:
+ To make a registration:
LISTEN virtual;
-LISTEN
NOTIFY virtual;
-NOTIFY
Asynchronous NOTIFY 'virtual' from backend with pid '8448' received
UNLISTEN virtual;
-UNLISTEN
NOTIFY virtual;
-NOTIFY
--- notice no NOTIFY event is received
+-- no NOTIFY event is received
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 1998-10-19
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no
UNLISTEN in
SQL92.
-
-
+
+
Compatibility
+
+ There is no UNLISTEN command in the SQL standard.
+
UPDATE
SQL - Language Statements
+
-
- UPDATE
-
-
- update rows of a table
-
+ UPDATE
+ update rows of a table
+
-
- 1999-07-20
-
-
-UPDATE [ ONLY ] table SET col = expression [, ...]
+
+UPDATE [ ONLY ] table SET column = expression [, ...]
[ FROM fromlist ]
[ WHERE condition ]
-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- table
-
- The name (optionally schema-qualified) of an existing table. If
- ONLY is specified, only that table is updated. If
- ONLY is not specified, the table and all its
- descendant tables (if any) are updated. * can be
- appended to the table name to indicate that descendant tables are
- to be scanned, but in the current version, this is the default
- behavior. (In releases before 7.1, ONLY was the
- default behavior.) The default can be altered by changing the
- configuration option.
-
-
-
-
- column
-
- The name of a column in table.
-
-
-
-
- expression
-
- A valid expression or value to assign to column.
-
-
-
-
- fromlist
-
- non-standard extension to allow columns
- from other tables to appear in the WHERE condition.
-
-
-
-
- condition
-
- Refer to the SELECT statement for a further description
- of the WHERE clause.
-
-
-
-
-
-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-UPDATE #
-
-
- Message returned if successful.
- The #
- means the number of rows updated.
- If #
- is 0 no rows are updated.
-
-
-
-
-
-
+
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
- UPDATE changes the values of the columns specified for
- all rows which satisfy condition. Only the columns
- to be modified need appear as columns in the statement.
-
+
+
Description
- Array references use the same syntax found in
- .
- That is, either single array elements, a range of array
- elements or the entire array may be replaced with a single
- query.
+ UPDATE changes the values of the specified
+ columns in all rows that satisfy the condition. Only the columns to
+ be modified need appear as columns in the statement.
- You must have write access to the table in order to modify
- it, as well as read access to any table whose values are
- mentioned in the WHERE condition.
+ By default, UPDATE will update rows in the
+ specified table and all its subtables. If you wish to only update
+ the specific table mentioned, you must use the ONLY
+ clause.
- By default UPDATE will update tuples in the table specified
- and all its sub-tables. If you wish to only update the
- specific table mentioned, you should use the ONLY clause.
+ You must have the UPDATE privilege on the table
+ to update it, as well as the SELECT
+ privilege to any table whose values are read in the
+ class="parameter">condition.
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Parameters
+
+
+
+ table
+
+ The name (optionally schema-qualified) of the table to update.
+
+
+
+
+
+ column
+
+ The name of a column in table.
+
+
+
+
+
+ expression
+
+ An expression or value to assign to the column.
+
+
+
+
+
+ fromlist
+
+ A list of table expressions, allowing columns from other tables
+ to appear in the WHERE condition.
+
+
+
+
+
+ condition
+
+ A value expression that returns a value of type
+ boolean that determines the rows which are to be
+ updated.
+
+
+
+
+
+
+
+
Diagnostics
+
+
+
+ UPDATE count
+
+ Message returned if successful. The value
+ class="parameter">count is the number of rows
+ updated. If count
+ is 0, no rows were updated.
+
+
+
+
+
+
+
+
Examples
- Change word Drama with Dramatic on column kind:
+ Change the word Drama to Dramatic in the
+ column kind of the table films:
-UPDATE films
-SET kind = 'Dramatic'
-WHERE kind = 'Drama';
-SELECT *
-FROM films
-WHERE kind = 'Dramatic' OR kind = 'Drama';
-
- code | title | did | date_prod | kind | len
--------+---------------+-----+------------+----------+-------
- BL101 | The Third Man | 101 | 1949-12-23 | Dramatic | 01:44
- P_302 | Becket | 103 | 1964-02-03 | Dramatic | 02:28
- M_401 | War and Peace | 104 | 1967-02-12 | Dramatic | 05:57
- T_601 | Yojimbo | 106 | 1961-06-16 | Dramatic | 01:50
- DA101 | Das Boot | 110 | 1981-11-11 | Dramatic | 02:29
+UPDATE filme SET kind = 'Dramatic' WHERE kind = 'Drama';
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 1998-09-24
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
-
SQL92 defines a different syntax for
- the positioned UPDATE statement:
-
-
-UPDATE table SET column = expression [, ...]
- WHERE CURRENT OF cursor
-
-
- where cursor
- identifies an open cursor.
-
-
+
+
Compatibility
+
+ This command conforms to the SQL standard. The
+ FROM clause is a PostgreSQL extension.
+
VACUUM
SQL - Language Statements
+
-
- VACUUM
-
-
- garbage-collect and optionally analyze a database
-
+ VACUUM
+ garbage-collect and optionally analyze a database
+
-
- 2001-08-26
-
-
+
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ table ]
VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] ANALYZE [ table [ (column [, ...] ) ] ]
-
-
-
-
- 2001-07-10
-
-
</div>
<div class="diff rem">- Inputs</div>
<div class="diff rem">-
-
-
-
- FULL
-
- Selects full
vacuum, which may reclaim more space,
- but takes much longer and exclusively locks the table.
-
-
-
-
- FREEZE
-
- Selects aggressive freezing
of tuples.
-
-
-
-
- VERBOSE
-
- Prints a detailed vacuum activity report for each table.
-
-
-
-
- ANALYZE
-
- Updates statistics used by the optimizer to
- determine the most efficient way to execute a query.
-
-
-
-
- table
-
- The name (optionally schema-qualified) of a specific table to
- vacuum. Defaults to all tables in the current database.
-
-
-
-
- column
-
- The name of a specific column to analyze. Defaults to all columns.
-
-
-
-
-
-
-
-
-
- 1998-10-04
-
-
</div>
<div class="diff rem">- Outputs</div>
<div class="diff rem">-
-
-
-
-
-VACUUM
-
-
- The command is complete.
-
-
-
-
-
-
-INFO: --Relation table--
-
-
- The report header for table.
-
-
-
-
-
-
-INFO: Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
- Tup 1000: Vac 3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188;
- Re-using: Free/Avail. Space 586952/586952; EndEmpty/Avail. Pages 0/74.
- Elapsed 0/0 sec.
-
-
- The analysis for table itself.
-
-
-
-
-
-
-INFO: Index index: Pages 28;
- Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
-
-
- The analysis for an index on the target table.
-
-
-
-
-
-
+
-
-
- 2001-07-10
-
-
</div>
<div class="diff rem">- Description</div>
<div class="diff rem">-
+
+
Description
+
VACUUM reclaims storage occupied by deleted tuples.
In normal
PostgreSQL operation, tuples that
- are deleted or obsoleted by UPDATE are not physically removed from
+ are deleted or obsoleted by an update are not physically removed from
their table; they remain present until a VACUUM is
done. Therefore it's necessary to do VACUUM
periodically, especially on frequently-updated tables.
are no other open transactions in the same database, then it is guaranteed
that all tuples in the database are frozen and will not be
subject to transaction ID wraparound problems, no matter how long the
- database is left un-vacuumed.
+ database is left unvacuumed.
FREEZE is not recommended for routine use. Its only
intended usage is in connection with preparation of user-defined template
databases, or other databases that are completely read-only and will not
receive routine maintenance VACUUM operations.
See for details.
+
+
+
+
Parameters
+
+
+
+ FULL
+
+ Selects full
vacuum, which may reclaim more
+ space, but takes much longer and exclusively locks the table.
+
+
+
+
+
+ FREEZE
+
+ Selects aggressive freezing
of tuples.
+
+
+
+
+
+ VERBOSE
+
+ Prints a detailed vacuum activity report for each table.
+
+
+
+
+
+ ANALYZE
+
+ Updates statistics used by the planner to determine the most
+ efficient way to execute a query.
+
+
+
+
+
+ table
+
+ The name (optionally schema-qualified) of a specific table to
+ vacuum. Defaults to all tables in the current database.
+
+
+
-
-
- 2001-07-10
-
-
</div>
<div class="diff rem">- Notes</div>
<div class="diff rem">-
+
+ column
+
+ The name of a specific column to analyze. Defaults to all columns.
+
+
+
+
+
+
+
+
Diagnostics
+
+
+
+ VACUUM
+
+ The command is complete.
+
+
+
+
+
+ INFO: --Relation table--
+
+ The report header for table.
+
+
+
+
+
+ INFO: Pages 98: Changed 25, Reapped 74, Empty 0, New 0;
+ Tup 1000: Vac 3000, Crash 0, UnUsed 0, MinLen 188, MaxLen 188;
+ Re-using: Free/Avail. Space 586952/586952; EndEmpty/Avail. Pages 0/74.
+ Elapsed 0/0 sec.
+
+ The analysis for table itself.
+
+
+
+
+
+ INFO: Index index: Pages 28;
+ Tuples 1000: Deleted 3000. Elapsed 0/0 sec.
+
+ The analysis for an index on the target table.
+
+
+
+
+
+
+
+
Notes
We recommend that active production databases be
- VACUUM-ed frequently (at least nightly), in order to
+ vacuumed frequently (at least nightly), in order to
remove expired rows. After adding or deleting a large number
- of records, it may be a good idea to issue a VACUUM
+ of rows, it may be a good idea to issue a VACUUM
ANALYZE command for the affected table. This will update the
system catalogs with
the results of all recent changes, and allow the
-
PostgreSQL query
optimizer to make better
- choices in planning user queries.
+
PostgreSQL query
planner to make better
+ choices in planning queries.
to occupy less disk space. VACUUM FULL will usually
shrink the table more than a plain VACUUM would.
-
-
-
-
</div>
<div class="diff rem">- Usage</div>
<div class="diff rem">-
+
+
Examples
+
The following is an example from running VACUUM on a table
in the regression database:
-regression=> VACUUM VERBOSE ANALYZE onek;
+=> VACUUM VERBOSE ANALYZE onek;
INFO: --Relation onek--
INFO: Index onek_unique1: Pages 14; Tuples 1000: Deleted 3000.
CPU 0.00s/0.11u sec elapsed 0.12 sec.
Total CPU 0.05s/0.45u sec elapsed 0.59 sec.
INFO: Analyzing onek
VACUUM
-
+
-
-
</div>
<div class="diff rem">- Compatibility</div>
<div class="diff rem">-
-
-
-
- 1998-10-04
-
-
</div>
<div class="diff rem">- SQL92</div>
<div class="diff rem">-
- There is no
VACUUM statement in
SQL92.
-
-
+
+
Compatibility
+
+ There is no VACUUM statement in the SQL standard.
+
projects / postgresql.git / commitdiff