79
Appendix E. Release Notes
E.206.4.1. Performance Improvements
•
Support cross-data-type index usage (Tom)
Before this change, many queries would not use an index if the data types did not match exactly.
This improvement makes index usage more intuitive and consistent.
•
New buffer replacement strategy that improves caching (Jan)
Prior releases useda least-recently-used(LRU) cache to keep recentlyreferencedpages inmemory.
The LRU algorithm did not consider the number of times a specific cache entry was accessed, so
large table scans could force out useful cache pages. The new cache algorithm uses four separate
lists to track most recently used and most frequently used cache pages and dynamically optimize
their replacement based on the workload. This should lead tomuch more efficient useof theshared
buffer cache. Administrators who have tested shared buffer sizes in the past should retest with this
new cache replacement policy.
•
Add subprocess to write dirty buffers periodically to reduce checkpoint writes (Jan)
In previous releases, the checkpoint process, which runs every few minutes, would write all dirty
buffers to the operating system’s buffer cache then flush all dirty operating system buffers to disk.
This resulted in a periodic spike in disk usage that often hurt performance. The new code uses a
background writer to trickle disk writes at a steady pace so checkpoints have far fewer dirty pages
to write to disk. Also, the new code does not issue a global
sync()
call, but instead
fsync()
s
just the files written since the last checkpoint. This should improve performance and minimize
degradation during checkpoints.
•
Add ability to prolong vacuum to reduce performance impact (Jan)
On busy systems,
VACUUM
performs manyI/O requests which canhurt performance for other users.
This release allows you to slow down
VACUUM
to reduce its impact on other users, though this
increases the total duration of
VACUUM
.
•
Improve B-tree index performance for duplicate keys (DmitryTkach, Tom)
This improves the way indexes are scanned when many duplicate values exist in the index.
•
Use dynamically-generated table size estimates while planning (Tom)
Formerly the planner estimated table sizes using the values seen by the last
VACUUM
or
ANALYZE
,
both as to physical table size (number of pages) and number of rows. Now, the current physical
table size is obtained from the kernel, and the number of rows is estimated by multiplying the
table size by the row density (rows per page) seen by the last
VACUUM
or
ANALYZE
.This should
produce more reliable estimates in cases where the table size has changed significantly since the
last housekeeping command.
•
Improved index usage with
OR
clauses (Tom)
This allows the optimizer to use indexes in statements with many OR clauses that would not have
been indexed in the past. It can also use multi-column indexes where the first column is specified
and the second column is part of an
OR
clause.
•
Improve matching of partial index clauses (Tom)
The server is now smarter about using partial indexes in queries involving complex
WHERE
clauses.
•
Improve performance of the GEQO optimizer (Tom)
The GEQO optimizer is used to plan queries involving many tables (by default, twelve or more).
This release speeds up the way queries are analyzed to decrease time spent in optimization.
•
Miscellaneous optimizer improvements
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102
Appendix E. Release Notes
There is not room here to list all the minor improvements made, but numerous special cases work
better than in prior releases.
•
Improve lookup speed for C functions (Tom)
This release uses a hash table to lookup information for dynamically loaded C functions. This
improves their speed so they perform nearly as quickly as functions that are built into the server
executable.
•
Add type-specific
ANALYZE
statistics capability (Mark Cave-Ayland)
This feature allows more flexibility in generating statistics for nonstandard data types.
•
ANALYZE
now collects statistics for expression indexes (Tom)
Expression indexes (also called functional indexes) allow users to index not just columns but the
results of expressions and function calls. With this release, the optimizer can gather and use statis-
tics about the contents of expression indexes. This will greatly improve the quality of planning for
queries in which an expression index is relevant.
•
New two-stage sampling method for
ANALYZE
(Manfred Koizar)
This gives better statistics when the density of valid rows is very different in different regions of a
table.
•
Speedup
TRUNCATE
(Tom)
This buys back some of the performance loss observed in 7.4, while still keeping
TRUNCATE
transaction-safe.
E.206.4.2. Server Changes
•
Add WAL file archiving and point-in-time recovery (Simon Riggs)
•
Add tablespaces so admins can control disk layout (Gavin)
•
Add a built-in log rotation program (Andreas Pflug)
It is now possible to log server messages conveniently without relying on either syslogor an exter-
nal log rotation program.
•
Add new read-only server configuration parameters to show server compile-time settings:
block_size
,
integer_datetimes
,
max_function_args
,
max_identifier_length
,
max_index_keys
(Joe)
•
Make quoting of
sameuser
,
samegroup
,and
all
remove special meaning of these terms in
pg_hba.conf
(Andrew)
•
Use clearer IPv6 name
::1/128
for
localhost
indefault
pg_hba.conf
(Andrew)
•
Use CIDR format in
pg_hba.conf
examples (Andrew)
•
Rename server configuration parameters
SortMem
and
VacuumMem
to
work_mem
and
maintenance_work_mem
(Old names still supported) (Tom)
This change was made to clarify that bulk operations such as index and foreign key creation use
maintenance_work_mem
,while
work_mem
is for workspaces used during query execution.
•
Allow logging of session disconnections using server configuration
log_disconnections
(An-
drew)
•
Add new server configuration parameter
log_line_prefix
to allow control of information emit-
ted in each log line (Andrew)
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113
Appendix E. Release Notes
Available information includes user name, database name, remote IP address, and session start
time.
•
Remove server configuration parameters
log_pid
,
log_timestamp
,
log_source_port
;func-
tionality superseded by
log_line_prefix
(Andrew)
•
Replace the
virtual_host
and
tcpip_socket
parameters with a unified
listen_addresses
parameter (Andrew, Tom)
virtual_host
could only specify a single IP address to listen on.
listen_addresses
allows
multiple addresses to be specified.
•
Listen on localhost by default, which eliminates the need for the
-i
postmaster switch in many
scenarios (Andrew)
Listening on localhost (
127.0.0.1
)opens no new security holes but allows configurations like
Windows and JDBC, whichdo not support local sockets, to work without special adjustments.
•
Remove
syslog
server configuration parameter, and add more logical
log_destination
vari-
able to control log output location (Magnus)
•
Change server configuration parameter
log_statement
to take values
all
,
mod
,
ddl
,or
none
to
select which queries are logged (Bruce)
This allows administrators to log onlydata definitionchanges or only data modification statements.
•
Some logging-related configuration parameters could formerly be adjusted by ordinary users, but
only in the “more verbose” direction. They are now treated more strictly: only superusers can set
them. However, a superuser can use
ALTER USER
to provide per-user settings of these values for
non-superusers. Also, it is now possiblefor superusers to setvalues of superuser-onlyconfiguration
parameters via
PGOPTIONS
.
•
Allow configuration files to be placed outside the data directory (mlw)
By default, configuration files are kept in the cluster’s top directory. With this addition, configura-
tion files can be placed outside the data directory, easing administration.
•
Planpreparedqueries onlywhen firstexecuted soconstants canbeusedfor statistics (Oliver Jowett)
Prepared statements plan queries once and execute them many times. While prepared queries avoid
the overhead of re-planningon eachuse, the quality of the plan suffers from notknowing the exact
parameters to be used in the query. In this release, planning of unnamed prepared statements is
delayed until the first execution, and the actual parameter values of that execution are used as op-
timization hints. This allows use of out-of-line parameter passing without incurring a performance
penalty.
•
Allow
DECLARE CURSOR
to take parameters (Oliver Jowett)
It is now useful to issue
DECLARE CURSOR
in a
Parse
message with parameters. The parameter
values sent at
Bind
time will be substituted into the execution of the cursor’s query.
•
Fix hash joins and aggregates of
inet
and
cidr
data types (Tom)
Release 7.4 handled hashingof mixed
inet
and
cidr
values incorrectly. (This bug did not exist in
prior releases because they wouldn’t try to hash either data type.)
•
Make
log_duration
print only when
log_statement
prints the query (Ed L.)
E.206.4.3. Query Changes
•
Add savepoints (nested transactions) (Alvaro)
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87
Appendix E. Release Notes
•
Unsupported isolation levels are now accepted and promoted to the nearest supported level (Peter)
The SQL specification states that if a database doesn’t support a specific isolation level, it should
use the next more restrictive level. This change complies with that recommendation.
•
Allow
BEGIN WORK
tospecifytransactionisolation levels like
START TRANSACTION
does (Bruce)
•
Fix table permission checking for cases in which rules generate a query type different from the
originally submitted query (Tom)
•
Implement dollar quoting to simplify single-quote usage (Andrew, Tom, David Fetter)
In previous releases, because single quotes had to be used to quote a function’s body, the use
of single quotes inside the function text required use of two single quotes or other error-prone
notations. With this release we add the ability to use "dollar quoting" to quote a block of text. The
ability to use different quoting delimiters at different nesting levels greatly simplifies the task of
quoting correctly, especially in complex functions. Dollar quoting can be used anywhere quoted
text is needed.
•
Make
CASE val WHEN compval1 THEN ...
evaluate
val
only once (Tom)
CASE
no longer evaluates the tested expression multiple times. This has benefits when the expres-
sion is complex or is volatile.
•
Test
HAVING
before computing target list of an aggregate query (Tom)
Fixes improper failure of cases such as
SELECT SUM(win)/SUM(lose) ... GROUP BY ...
HAVING SUM(lose) > 0
.This should work but formerly could fail with divide-by-zero.
•
Replace
max_expr_depth
parameter with
max_stack_depth
parameter, measured in kilobytes
of stack size (Tom)
This gives us a fairly bulletproof defense against crashing due to runaway recursive functions.
Instead of measuring the depth of expression nesting, we now directly measure the size of the
execution stack.
•
Allow arbitrary row expressions (Tom)
This release allows SQL expressions to contain arbitrary composite types, that is, row values. It
also allows functions tomore easily take rows as arguments and return row values.
•
Allow
LIKE
/
ILIKE
to be used as the operator in rowand subselect comparisons (Fabien Coelho)
•
Avoid locale-specific case conversion of basic ASCII letters in identifiers andkeywords (Tom)
This solves the “Turkish problem” with mangling of words containing
I
and
i
.Folding of charac-
ters outside the 7-bit-ASCII set is still locale-aware.
•
Improve syntax error reporting (Fabien, Tom)
Syntax error reports are more useful than before.
•
Change
EXECUTE
to return a completion tag matching the executed statement (Kris Jurka)
Previous releases return an
EXECUTE
tag for any
EXECUTE
call. In this release, the tag returnedwill
reflect the commandexecuted.
•
Avoid emitting
NATURAL CROSS JOIN
in rule listings (Tom)
Sucha clause makes no logical sense, but in some cases the rule decompiler formerly produced this
syntax.
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Appendix E. Release Notes
E.206.4.4. Object Manipulation Changes
•
Add
COMMENT ON
for casts, conversions, languages, operator classes, and large objects (Christo-
pher)
•
Add new server configuration parameter
default_with_oids
to control whether tables are cre-
ated with
OID
sby default (Neil)
This allows administrators to control whether
CREATE TABLE
commands create tables
with or without
OID
columns by default. (Note: the current factory default setting for
default_with_oids
is
TRUE
,but the default will become
FALSE
in future releases.)
•
Add
WITH
/
WITHOUT OIDS
clause to
CREATE TABLE AS
(Neil)
•
Allow
ALTER TABLE DROP COLUMN
to drop an
OID
column (
ALTER TABLE SET WITHOUT
OIDS
still works) (Tom)
•
Allow composite types as table columns (Tom)
•
Allow
ALTER ... ADD COLUMN
with defaults and
NOT NULL
constraints; works per SQL spec
(Rod)
It is now possible for
ADD COLUMN
to create a column that is not initially filled with NULLs, but
with a specified default value.
•
Add
ALTER COLUMN TYPE
to change column’s type (Rod)
It is now possible to alter a column’s data type without dropping and re-adding the column.
•
Allow multiple
ALTER
actions in a single
ALTER TABLE
command(Rod)
This is particularly useful for
ALTER
commands that rewrite the table (which include
ALTER
COLUMN TYPE
and
ADD COLUMN
with a default). By grouping
ALTER
commands together, the
table need be rewritten only once.
•
Allow
ALTER TABLE
to add
SERIAL
columns (Tom)
This falls out from the new capability of specifying defaults for new columns.
•
Allow changing the owners of aggregates, conversions, databases, functions, operators, operator
classes, schemas, types, and tablespaces (Christopher, Euler Taveira de Oliveira)
Previously this required modifying the system tables directly.
•
Allowtemporary objectcreation tobe limitedto
SECURITY DEFINER
functions (SeanChittenden)
•
Add
ALTER TABLE ... SET WITHOUT CLUSTER
(Christopher)
Prior to this release, there was no way to clear an auto-cluster specification except to modify the
system tables.
•
Constraint/Index/
SERIAL
names are now
table_column_type
with numbers appended to guar-
antee uniqueness within the schema (Tom)
The SQL specification states that such names should be unique within a schema.
•
Add
pg_get_serial_sequence()
to return a
SERIAL
column’s sequence name (Christopher)
This allows automated scripts to reliably find the
SERIAL
sequence name.
•
Warn when primary/foreign key data type mismatch requires costly lookup
•
New
ALTER INDEX
command to allow moving of indexes between tablespaces (Gavin)
•
Make
ALTER TABLE OWNER
change dependent sequence ownership too (Alvaro)
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Appendix E. Release Notes
E.206.4.5. Utility Command Changes
•
Allow
CREATE SCHEMA
to create triggers, indexes, and sequences (Neil)
•
Add
ALSO
keyword to
CREATE RULE
(Fabien Coelho)
This allows
ALSO
to be added to rule creation to contrast it with
INSTEAD
rules.
•
Add
NOWAIT
option to
LOCK
(Tatsuo)
This allows the
LOCK
command to fail if it would have to wait for the requested lock.
•
Allow
COPY
to read and write comma-separated-value (CSV) files (Andrew, Bruce)
•
Generate error if the
COPY
delimiter and NULL string conflict (Bruce)
•
GRANT
/
REVOKE
behavior follows the SQL spec more closely
•
Avoid locking conflict between
CREATE INDEX
and
CHECKPOINT
(Tom)
In 7.3 and 7.4, a long-running B-tree index build could block concurrent
CHECKPOINT
sfrom com-
pleting, thereby causing WAL bloat because the WAL log could not be recycled.
•
Database-wide
ANALYZE
does not hold locks across tables (Tom)
This reduces the potential for deadlocks against other backends thatwant exclusivelocks on tables.
To get the benefitof this change, donot execute database-wide
ANALYZE
inside a transaction block
(
BEGIN
block); it must be able to commit andstart a new transaction for each table.
•
REINDEX
does not exclusively lockthe index’s parent table anymore
The index itself is still exclusively locked, but readers of thetable can continueif theyare notusing
the particular index being rebuilt.
•
Erase MD5 user passwords when a user is renamed (Bruce)
PostgreSQL uses the user name as salt when encrypting passwords via MD5. When a user’s name
is changed, the salt willnolonger matchthe storedMD5password, so the stored password becomes
useless. In this releasea notice is generated and the password is cleared. A new passwordmustthen
be assigned if the user is to be able to log in with a password.
•
New pg_ctl
kill
option for Windows (Andrew)
Windows does not have a
kill
command to send signals to backends so this capability was added
to pg_ctl.
•
Information schema improvements
•
Add
--pwfile
option to initdb so the initial password can be set by GUI tools (Magnus)
•
Detect locale/encoding mismatch in initdb (Peter)
•
Add
register
command to pg_ctl to register Windows operating system service (Dave Page)
E.206.4.6. Data Type and Function Changes
•
More complete support for composite types (row types) (Tom)
Composite values can be used in many places where only scalar values worked before.
•
Reject nonrectangular array values as erroneous (Joe)
Formerly,
array_in
would silently build a surprising result.
•
Overflow in integer arithmetic operations is now detected (Tom)
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155
Appendix E. Release Notes
•
The arithmetic operators associated with the single-byte
"char"
data type have been removed.
Formerly, the parser would select these operators in many situations where an “unable to select
an operator” error would be more appropriate, such as
null
*
null
.If you actually want to do
arithmetic ona
"char"
column, you can cast it to integer explicitly.
•
Syntax checking of array input values considerably tightened up (Joe)
Junk thatwas previouslyallowed in odd places withodd results now causes an
ERROR
,for example,
non-whitespace after the closing right brace.
•
Empty-string array element values must now be written as
""
,rather than writing nothing (Joe)
Formerly, both ways of writing an empty-string element value were allowed, but now a quoted
empty string is required. The case where nothing at all appears will probably be considered to be a
NULL element value in some future release.
•
Array element trailing whitespace is nowignored (Joe)
Formerly leading whitespace was ignored, but trailing whitespace between an element value and
the delimiter or right brace was significant. Now trailing whitespace is also ignored.
•
Emit array values with explicit array bounds when lower bound is not one (Joe)
•
Accept
YYYY-monthname-DD
as a date string (Tom)
•
Make
netmask
and
hostmask
functions return maximum-lengthmask length (Tom)
•
Change factorial function to return
numeric
(Gavin)
Returning
numeric
allows the factorial function to work for a wider range of input values.
•
to_char
/
to_date()
date conversion improvements (Kurt Roeckx, Fabien Coelho)
•
Make
length()
disregard trailing spaces in
CHAR(n)
(Gavin)
This change was made to improve consistency: trailing spaces are semantically insignificant in
CHAR(n)
data, so they should not be counted by
length()
.
•
Warn about empty string being passed to
OID
/
float4
/
float8
data types (Neil)
8.1 will throw an error instead.
•
Allow leading or trailing whitespace in
int2
/
int4
/
int8
/
float4
/
float8
input routines (Neil)
•
Better support for IEEE
Infinity
and
NaN
values in
float4
/
float8
(Neil)
These shouldnow work on all platforms that support IEEE-compliant floating point arithmetic.
•
Add
week
option to
date_trunc()
(Robert Creager)
•
Fix
to_char
for
1 BC
(previously it returned
1 AD
)(Bruce)
•
Fix
date_part(year)
for BC dates (previously it returnedoneless thanthecorrectyear) (Bruce)
•
Fix
date_part()
to return the proper millennium and century (Fabien Coelho)
In previous versions, the century and millennium results had a wrong number and started in the
wrong year, as compared to standard reckoning of such things.
•
Add
ceiling()
as an alias for
ceil()
,and
power()
as an alias for
pow()
for standards compli-
ance (Neil)
•
Change
ln()
,
log()
,
power()
,and
sqrt()
to emit the correct
SQLSTATE
error codes for certain
error conditions, as specified by SQL:2003 (Neil)
•
Add
width_bucket()
function as defined by SQL:2003 (Neil)
•
Add
generate_series()
functions to simplify working with numeric sets (Joe)
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91
Appendix E. Release Notes
•
Fix
upper/lower/initcap()
functions to work with multibyte encodings (Tom)
•
Add boolean and bitwise integer
AND
/
OR
aggregates (Fabien Coelho)
•
New session information functions to return network addresses for client and server (Sean Chitten-
den)
•
Add functionto determine the area of a closed path (Sean Chittenden)
•
Add functionto send cancel request to other backends (Magnus)
•
Add
interval
plus
datetime
operators (Tom)
The reverse ordering,
datetime
plus
interval
,was already supported, but both are required by
the SQL standard.
•
Casting an integer to
BIT(N)
selects the rightmost N bits of the integer (Tom)
In prior releases, the leftmost N bits were selected, but this was deemed unhelpful, not to mention
inconsistent with casting from bit to int.
•
Require
CIDR
values to have all nonmasked bits be zero (Kevin Brintnall)
E.206.4.7. Server-Side Language Changes
•
In
READ COMMITTED
serialization mode, volatile functions nowsee theresults of concurrent trans-
actions committed up to the beginning of each statement within the function, rather than up to the
beginning of the interactive command that called the function.
•
Functions declared
STABLE
or
IMMUTABLE
always use the snapshotof the calling query, and there-
fore do not see the effects of actions taken after the calling query starts, whether in their own
transaction or other transactions. Sucha functionmustbe read-only, too, meaning that it cannotuse
any SQL commands other than
SELECT
.There is a considerable performance gain from declaring
afunction
STABLE
or
IMMUTABLE
rather than
VOLATILE
.
•
Nondeferred
AFTER
triggers are now fired immediately after completion of the triggering query,
rather than upon finishing the current interactive command. This makes a difference when the
triggering query occurred within a function: the trigger is invoked before the function proceeds to
its next operation. For example, if a functioninserts a newrowinto a table, any nondeferred foreign
key checks occur before proceeding with the function.
•
Allow functionparameters to be declared with names (Dennis Björklund)
This allows better documentation of functions. Whether the names actually do anything depends
on the specific function language being used.
•
Allow PL/pgSQL parameter names to be referenced in the function (Dennis Björklund)
This basically creates an automatic alias for each named parameter.
•
Do minimal syntax checking of PL/pgSQL functions at creation time (Tom)
This allows us to catch simple syntax errors sooner.
•
More support for composite types (row and record variables) in PL/pgSQL
For example, it now works to pass a rowtype variable to another function as a single variable.
•
Default values for PL/pgSQL variables can now reference previously declared variables
•
Improve parsing of PL/pgSQL FOR loops (Tom)
2597
Documents you may be interested
Documents you may be interested
