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docs: my third pass over the 9.6 release notes 

Backpatch-through: 9.6
This commit is contained in:
Bruce Momjian 2016-08-16 23:04:50 -04:00
parent 0bb51aa967
commit d125d25790
1 changed files with 331 additions and 295 deletions
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doc/src/sgml/release-9.6.sgml
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@ -401,7 +401,7 @@ This commit is also listed under libpq and psql
<para>
Allow <link linkend="GIN"><acronym>GIN</></> index builds to
make effective use of <xref linkend="guc-maintenance-work-mem">
settings larger than 1GB (Robert Abraham, Teodor Sigaev)
settings larger than 1 GB (Robert Abraham, Teodor Sigaev)
</para>
</listitem>
@ -467,7 +467,217 @@ This commit is also listed under libpq and psql
</sect4>
<sect4>
<title>General Performance</title>
<title>Sorting</title>
<itemizedlist>
<listitem>
<!--
2016-04-08 [071180377] Use quicksort, not replacement selection, for external s
2016-03-17 [0011c0091] Improve memory management for external sorts.
-->
<para>
Improve sorting performance by using quicksort, not replacement
selection sort, when performing external sort steps (Peter
Geoghegan)
</para>
<para>
The new approach makes better use of the <acronym>CPU</> cache
for typical cache sizes and data volumes. Where necessary,
the behavior can be adjusted via the new configuration parameter
<xref linkend="guc-replacement-sort-tuples">.
</para>
</listitem>
<listitem>
<!--
2015-10-09 [0e57b4d8b] Speed up text sorts where the same strings occur multipl
2015-10-20 [5be94a9eb] Be a bit more rigorous about how we cache strcoll and st
-->
<para>
Speed up text sorts where the same string occurs multiple times
(Peter Geoghegan)
</para>
</listitem>
<listitem>
<!--
2015-11-06 [a76ef15d9] Add sort support routine for the UUID data type.
2016-02-03 [b47b4dbf6] Extend sortsupport for text to more opclasses.
2016-02-17 [f1f5ec1ef] Reuse abbreviated keys in ordered [set] aggregates.
-->
<para>
Speed up sorting of <type>uuid</>, <type>bytea</>, and
<type>char(n)</> fields by using <quote>abbreviated</> keys
(Peter Geoghegan)
</para>
<para>
Support for abbreviated keys has also been
added to the non-default operator classes <link
linkend="indexes-opclass"><literal>text_pattern_ops</></>,
<literal>varchar_pattern_ops</>, and
<literal>bpchar_pattern_ops</>. Processing of ordered-set
aggregates can also now exploit abbreviated keys.
</para>
</listitem>
<listitem>
<!--
2015-12-16 [b648b7034] Speed up CREATE INDEX CONCURRENTLY's TID sort.
-->
<para>
Speed up <command>CREATE INDEX CONCURRENTLY</> by treating
<acronym>TID</>s as 64-bit integers during sorting (Peter
Geoghegan)
</para>
</listitem>
</itemizedlist>
</sect4>
<sect4>
<title>Locking</title>
<itemizedlist>
<listitem>
<!--
2015-08-06 [0e141c0fb] Reduce ProcArrayLock contention by removing backends in
2015-09-03 [4aec49899] Assorted code review for recent ProcArrayLock patch.
-->
<para>
Reduce contention for the <literal>ProcArrayLock</> (Amit Kapila,
Robert Haas)
</para>
</listitem>
<listitem>
<!--
2015-12-15 [6150a1b08] Move buffer I/O and content LWLocks out of the main tran
-->
<para>
Improve performance by moving buffer content locks into the buffer
descriptors (Andres Freund, Simon Riggs)
</para>
</listitem>
<listitem>
<!--
2016-04-10 [48354581a] Allow Pin/UnpinBuffer to operate in a lockfree manner.
-->
<para>
Replace shared-buffer header spinlocks with atomic operations to
improve scalability (Alexander Korotkov, Andres Freund)
</para>
</listitem>
<listitem>
<!--
2016-04-10 [008608b9d] Avoid the use of a separate spinlock to protect a LWLock
-->
<para>
Use atomic operations, rather than a spinlock, to protect an
<literal>LWLock</>'s wait queue (Andres Freund)
</para>
</listitem>
<listitem>
<!--
2016-03-23 [44ca4022f] Partition the freelist for shared dynahash tables.
-->
<para>
Partition the shared hash table freelist to reduce contention on
multi-<acronym>CPU</>-socket servers (Aleksander Alekseev)
</para>
</listitem>
<listitem>
<!--
2016-01-09 [687f2cd7a] Avoid pin scan for replay of XLOG_BTREE_VACUUM
2016-04-03 [3e4b7d879] Avoid pin scan for replay of XLOG_BTREE_VACUUM in all ca
-->
<para>
Reduce interlocking on standby servers during the replay of btree
index vacuuming operations (Simon Riggs)
</para>
<para>
This change avoids substantial replication delays that sometimes
occurred while replaying such operations.
</para>
</listitem>
</itemizedlist>
</sect4>
<sect4>
<title>Optimizer Statistics</title>
<itemizedlist>
<listitem>
<!--
2016-04-01 [be4b4dc75] Omit null rows when applying the Haas-Stokes estimator f
2016-04-01 [3d3bf62f3] Omit null rows when setting the threshold for what's a m
2016-04-04 [391159e03] Partially revert commit 3d3bf62f30200500637b24fdb7b992a9
-->
<para>
Improve <command>ANALYZE</>'s estimates for columns with many nulls
(Tomas Vondra, Alex Shulgin)
</para>
<para>
Previously <command>ANALYZE</> tended to underestimate the number
of non-<literal>NULL</> distinct values in a column with many
<literal>NULL</>s, and was also inaccurate in computing the
most-common values.
</para>
</listitem>
<listitem>
<!--
2016-04-04 [84f9a35e3] Improve estimate of distinct values in estimate_num_grou
-->
<para>
Improve planner's estimate of the number of distinct values in
a query result (Tomas Vondra)
</para>
</listitem>
<listitem>
<!--
2016-04-08 [137805f89] Use Foreign Key relationships to infer multi-column join
2016-06-07 [77ba61080] Revert "Use Foreign Key relationships to infer multi-col
2016-06-18 [100340e2d] Restore foreign-key-aware estimation of join relation si
-->
<para>
Use foreign key relationships to infer selectivity for join
predicates (Tomas Vondra, David Rowley)
</para>
<para>
If a table <literal>t</> has a foreign key restriction, say
<literal>(a,b) REFERENCES r (x,y)</>, then a <literal>WHERE</>
condition such as <literal>t.a = r.x AND t.b = r.y</> cannot
select more than one <literal>r</> row per <literal>t</> row.
The planner formerly considered <literal>AND</> conditions
to be independent and would often drastically misestimate
selectivity as a result. Now it compares the <literal>WHERE</>
conditions to applicable foreign key constraints and produces
better estimates.
</para>
</listitem>
</itemizedlist>
</sect4>
<sect4>
<title><command>VACUUM</></title>
<itemizedlist>
@ -519,19 +729,40 @@ This commit is also listed under libpq and psql
</para>
</listitem>
</itemizedlist>
</sect4>
<sect4>
<title>General Performance</title>
<itemizedlist>
<listitem>
<!--
2016-01-09 [687f2cd7a] Avoid pin scan for replay of XLOG_BTREE_VACUUM
2016-04-03 [3e4b7d879] Avoid pin scan for replay of XLOG_BTREE_VACUUM in all ca
2016-04-08 [848ef42bb] Add the "snapshot too old" feature
2016-05-06 [2cc41acd8] Fix hash index vs "snapshot too old" problemms
2016-05-06 [7e3da1c47] Mitigate "snapshot too old" performance regression on NU
2016-08-03 [3e2f3c2e4] Prevent "snapshot too old" from trying to return pruned
2016-08-07 [9ee1cf04a] Fix TOAST access failure in RETURNING queries.
-->
<para>
Reduce interlocking on standby servers during the replay of btree
index vacuuming operations (Simon Riggs)
Allow old <acronym>MVCC</> snapshots to be invalidated after a
configurable timeout (Kevin Grittner)
</para>
<para>
This change avoids substantial replication delays that sometimes
occurre while replaying such operations.
Normally, deleted tuples cannot be physically removed by
vacuuming until the last transaction that could <quote>see</>
them is gone. A transaction that stays open for a long
time can thus cause considerable table bloat because
space cannot be recycled. This feature allows setting
a time-based limit, via the new configuration parameter
<xref linkend="guc-old-snapshot-threshold">, on how long an
<acronym>MVCC</> snapshot is guaranteed to be valid. After that,
dead tuples are candidates for removal. A transaction using an
outdated snapshot will get an error if it attempts to read a page
that potentially could have contained such data.
</para>
</listitem>
@ -576,6 +807,45 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-03-31 [f9aefcb91] Support using index-only scans with partial indexes in m
-->
<para>
Allow use of an <link linkend="indexes-index-only-scans">index-only
scan</link> on a partial index when the index's <literal>WHERE</>
clause references columns which are not indexed (Tomas Vondra,
Kyotaro Horiguchi)
</para>
<para>
For example, <command>CREATE INDEX tidx_partial ON t(b) WHERE a
&gt; 0</> could not previously be used for an index-only scan by a
query that only referenced <literal>a</> in its <literal>WHERE</>
clause because <literal>a</> is not an indexed value like
<literal>b</> is.
</para>
</listitem>
<listitem>
<!--
2016-03-10 [9cd00c457] Checkpoint sorting and balancing.
-->
<para>
Perform checkpoint writes in sorted order (Fabien Coelho,
Andres Freund)
</para>
<para>
Previously, checkpoints wrote out dirty pages in whatever order
they happen to appear in shared buffers, which usually is nearly
random. That performs poorly, especially on rotating media.
This change causes checkpoint-driven writes to be done in order
by file and block number, and to be balanced across tablespaces.
</para>
</listitem>
<listitem>
<!--
2016-03-10 [428b1d6b2] Allow to trigger kernel writeback after a configurable n
2016-04-13 [fa11a09fe] Fix assorted portability issues with using msync() for d
2016-04-24 [8f91d87d4] Fix documentation & config inconsistencies around 428b1d
@ -620,97 +890,6 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-03-10 [9cd00c457] Checkpoint sorting and balancing.
-->
<para>
Perform checkpoint writes in sorted order (Fabien Coelho,
Andres Freund)
</para>
<para>
Previously, checkpoints wrote out dirty pages in whatever order
they happen to appear in shared buffers, which usually is nearly
random. That performs poorly, especially on rotating media.
This change causes checkpoint-driven writes to be done in order
by file and block number, and to be balanced across tablespaces.
</para>
</listitem>
<listitem>
<!--
2016-04-08 [848ef42bb] Add the "snapshot too old" feature
2016-05-06 [2cc41acd8] Fix hash index vs "snapshot too old" problemms
2016-05-06 [7e3da1c47] Mitigate "snapshot too old" performance regression on NU
2016-08-03 [3e2f3c2e4] Prevent "snapshot too old" from trying to return pruned
2016-08-07 [9ee1cf04a] Fix TOAST access failure in RETURNING queries.
-->
<para>
Allow old <acronym>MVCC</> snapshots to be invalidated after a
configurable timeout (Kevin Grittner)
</para>
<para>
Normally, deleted tuples cannot be physically removed by
vacuuming until the last transaction that could <quote>see</>
them is gone. A transaction that stays open for a long
time can thus cause considerable table bloat because
space cannot be recycled. This feature allows setting
a time-based limit, via the new configuration parameter
<xref linkend="guc-old-snapshot-threshold">, on how long an
<acronym>MVCC</> snapshot is guaranteed to be valid. After that,
dead tuples are candidates for removal. A transaction using an
outdated snapshot will get an error if it attempts to read a page
that potentially could have contained such data.
</para>
</listitem>
<listitem>
<!--
2016-03-31 [f9aefcb91] Support using index-only scans with partial indexes in m
-->
<para>
Allow use of an <link linkend="indexes-index-only-scans">index-only
scan</link> on a partial index when the index's <literal>WHERE</>
clause references columns which are not indexed (Tomas Vondra,
Kyotaro Horiguchi)
</para>
<para>
For example, <command>CREATE INDEX tidx_partial ON t(b) WHERE a
&gt; 0</> could not previously be used for an index-only scan by a
query that only referenced <literal>a</> in its <literal>WHERE</>
clause because <literal>a</> is not an indexed value like
<literal>b</> is.
</para>
</listitem>
<listitem>
<!--
2016-04-08 [137805f89] Use Foreign Key relationships to infer multi-column join
2016-06-07 [77ba61080] Revert "Use Foreign Key relationships to infer multi-col
2016-06-18 [100340e2d] Restore foreign-key-aware estimation of join relation si
-->
<para>
Use foreign key relationships to infer selectivity for join
predicates (Tomas Vondra, David Rowley)
</para>
<para>
If a table <literal>t</> has a foreign key restriction, say
<literal>(a,b) REFERENCES r (x,y)</>, then a <literal>WHERE</>
condition such as <literal>t.a = r.x AND t.b = r.y</> cannot
select more than one <literal>r</> row per <literal>t</> row.
The planner formerly considered <literal>AND</> conditions
to be independent and would often drastically misestimate
selectivity as a result. Now it compares the <literal>WHERE</>
conditions to applicable foreign key constraints and produces
better estimates.
</para>
</listitem>
<listitem>
<!--
2015-08-04 [804163bc2] Share transition state between different aggregates when
-->
<para>
@ -808,35 +987,6 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-04-01 [be4b4dc75] Omit null rows when applying the Haas-Stokes estimator f
2016-04-01 [3d3bf62f3] Omit null rows when setting the threshold for what's a m
2016-04-04 [391159e03] Partially revert commit 3d3bf62f30200500637b24fdb7b992a9
-->
<para>
Improve <command>ANALYZE</>'s estimates for columns with many nulls
(Tomas Vondra, Alex Shulgin)
</para>
<para>
Previously <command>ANALYZE</> tended to underestimate the number
of non-<literal>NULL</> distinct values in a column with many
<literal>NULL</>s, and was also inaccurate in computing the
most-common values.
</para>
</listitem>
<listitem>
<!--
2016-04-04 [84f9a35e3] Improve estimate of distinct values in estimate_num_grou
-->
<para>
Improve planner's estimate of the number of distinct values in
a query result (Tomas Vondra)
</para>
</listitem>
<listitem>
<!--
2016-04-08 [719c84c1b] Extend relations multiple blocks at a time to improve sc
-->
<para>
@ -851,69 +1001,6 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-04-08 [071180377] Use quicksort, not replacement selection, for external s
2016-03-17 [0011c0091] Improve memory management for external sorts.
-->
<para>
Improve sorting performance by using quicksort, not replacement
selection sort, when performing external sort steps (Peter
Geoghegan)
</para>
<para>
The new approach makes better use of the <acronym>CPU</> cache
for typical cache sizes and data volumes. Where necessary,
the behavior can be adjusted via the new configuration parameter
<xref linkend="guc-replacement-sort-tuples">.
</para>
</listitem>
<listitem>
<!--
2015-10-09 [0e57b4d8b] Speed up text sorts where the same strings occur multipl
2015-10-20 [5be94a9eb] Be a bit more rigorous about how we cache strcoll and st
-->
<para>
Speed up text sorts where the same string occurs multiple times
(Peter Geoghegan)
</para>
</listitem>
<listitem>
<!--
2015-11-06 [a76ef15d9] Add sort support routine for the UUID data type.
2016-02-03 [b47b4dbf6] Extend sortsupport for text to more opclasses.
2016-02-17 [f1f5ec1ef] Reuse abbreviated keys in ordered [set] aggregates.
-->
<para>
Speed up sorting of <type>uuid</>, <type>bytea</>, and
<type>char(n)</> fields by using <quote>abbreviated</> keys
(Peter Geoghegan)
</para>
<para>
Support for abbreviated keys has also been
added to the non-default operator classes <link
linkend="indexes-opclass"><literal>text_pattern_ops</></>,
<literal>varchar_pattern_ops</>, and
<literal>bpchar_pattern_ops</>. Processing of ordered-set
aggregates can also now exploit abbreviated keys.
</para>
</listitem>
<listitem>
<!--
2015-12-16 [b648b7034] Speed up CREATE INDEX CONCURRENTLY's TID sort.
-->
<para>
Speed up <command>CREATE INDEX CONCURRENTLY</> by treating
<acronym>TID</>s as 64-bit integers during sorting (Peter
Geoghegan)
</para>
</listitem>
<listitem>
<!--
2016-04-08 [5364b357f] Increase maximum number of clog buffers.
-->
<para>
@ -924,57 +1011,6 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2015-08-06 [0e141c0fb] Reduce ProcArrayLock contention by removing backends in
2015-09-03 [4aec49899] Assorted code review for recent ProcArrayLock patch.
-->
<para>
Reduce contention for the <literal>ProcArrayLock</> (Amit Kapila,
Robert Haas)
</para>
</listitem>
<listitem>
<!--
2015-12-15 [6150a1b08] Move buffer I/O and content LWLocks out of the main tran
-->
<para>
Improve performance by moving buffer content locks into the buffer
descriptors (Andres Freund, Simon Riggs)
</para>
</listitem>
<listitem>
<!--
2016-04-10 [48354581a] Allow Pin/UnpinBuffer to operate in a lockfree manner.
-->
<para>
Replace shared-buffer header spinlocks with atomic operations to
improve scalability (Alexander Korotkov, Andres Freund)
</para>
</listitem>
<listitem>
<!--
2016-04-10 [008608b9d] Avoid the use of a separate spinlock to protect a LWLock
-->
<para>
Use atomic operations, rather than a spinlock, to protect an
<literal>LWLock</>'s wait queue (Andres Freund)
</para>
</listitem>
<listitem>
<!--
2016-03-23 [44ca4022f] Partition the freelist for shared dynahash tables.
-->
<para>
Partition the shared hash table freelist to reduce contention on
multi-<acronym>CPU</>-socket servers (Aleksander Alekseev)
</para>
</listitem>
<listitem>
<!--
2015-07-05 [6c82d8d1f] Further reduce overhead for passing plpgsql variables to
-->
<para>
@ -1017,6 +1053,21 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-03-05 [dc7d70ea0] Expose control file data via SQL accessible functions.
-->
<para>
Add <link
linkend="functions-controldata"><function>pg_control_system()</></>,
<function>pg_control_checkpoint()</>,
<function>pg_control_recovery()</>, and
<function>pg_control_init()</> functions to expose fields of
<filename>pg_control</> to <acronym>SQL</> (Joe Conway, Michael
Paquier)
</para>
</listitem>
<listitem>
<!--
2016-02-17 [a5c43b886] Add new system view, pg_config
-->
<para>
@ -1082,21 +1133,6 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-03-05 [dc7d70ea0] Expose control file data via SQL accessible functions.
-->
<para>
Add <link
linkend="functions-controldata"><function>pg_control_system()</></>,
<function>pg_control_checkpoint()</>,
<function>pg_control_recovery()</>, and
<function>pg_control_init()</> functions to expose fields of
<filename>pg_control</> to <acronym>SQL</> (Joe Conway, Michael
Paquier)
</para>
</listitem>
<listitem>
<!--
2016-01-12 [e63bb4549] Add new user fn pg_current_xlog_flush_location()
-->
<para>
@ -1219,18 +1255,18 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-02-02 [7d17e683f] Add support for systemd service notifications
2016-03-16 [c6dda1f48] Add idle_in_transaction_session_timeout.
-->
<para>
Add configure option <option>--with-systemd</> to enable
calling <function>sd_notify()</> at server start and stop (Peter
Eisentraut)
Allow sessions to be terminated automatically if they are in
idle-in-transaction state for too long (Vik Fearing)
</para>
<para>
This allows the use of <application>systemd</> service units of
type <literal>notify</>, which greatly simplifies the management
of <productname>PostgreSQL</> under <application>systemd</>.
This behavior is controlled by the new configuration parameter
<xref linkend="guc-idle-in-transaction-session-timeout">. It can
be useful to prevent forgotten transactions from holding locks
or preventing vacuum cleanup for too long.
</para>
</listitem>
@ -1247,18 +1283,18 @@ This commit is also listed under libpq and psql
<listitem>
<!--
2016-03-16 [c6dda1f48] Add idle_in_transaction_session_timeout.
2016-02-02 [7d17e683f] Add support for systemd service notifications
-->
<para>
Allow sessions to be terminated automatically if they are in
idle-in-transaction state for too long (Vik Fearing)
Add configure option <option>--with-systemd</> to enable
calling <function>sd_notify()</> at server start and stop (Peter
Eisentraut)
</para>
<para>
This behavior is controlled by the new configuration parameter
<xref linkend="guc-idle-in-transaction-session-timeout">. It can
be useful to prevent forgotten transactions from holding locks
or preventing vacuum cleanup for too long.
This allows the use of <application>systemd</> service units of
type <literal>notify</>, which greatly simplifies the management
of <productname>PostgreSQL</> under <application>systemd</>.
</para>
</listitem>
@ -1857,6 +1893,30 @@ XXX this is pending backpatch, may need to remove
<listitem>
<!--
2016-04-07 [bb140506d] Phrase full text search.
2016-06-27 [028350f61] Make exact distance match for FTS phrase operator
2016-06-27 [3dbbd0f02] Do not fallback to AND for FTS phrase operator.
2016-06-27 [6734a1cac] Change predecence of phrase operator.
-->
<para>
Improve full-text search to support searching for phrases, that
is, lexemes appearing adjacent to each other in a specific order,
or with a specified distance between them (Teodor Sigaev, Oleg
Bartunov, Dmitry Ivanov)
</para>
<para>
A phrase-search query can be specified in <type>tsquery</>
input using the new operators <literal>&lt;-&gt;</> and
<literal>&lt;<replaceable>N</>&gt;</literal>. The former means
that the lexemes before and after it must appear adjacent to
each other in that order. The latter means they must be exactly
<replaceable>N</> lexemes apart.
</para>
</listitem>
<listitem>
<!--
2015-12-22 [6efbded6e] Allow omitting one or both boundaries in an array slice
-->
<para>
@ -1917,30 +1977,6 @@ XXX this is pending backpatch, may need to remove
<listitem>
<!--
2016-04-07 [bb140506d] Phrase full text search.
2016-06-27 [028350f61] Make exact distance match for FTS phrase operator
2016-06-27 [3dbbd0f02] Do not fallback to AND for FTS phrase operator.
2016-06-27 [6734a1cac] Change predecence of phrase operator.
-->
<para>
Improve full-text search to support searching for phrases, that
is, lexemes appearing adjacent to each other in a specific order,
or with a specified distance between them (Teodor Sigaev, Oleg
Bartunov, Dmitry Ivanov)
</para>
<para>
A phrase-search query can be specified in <type>tsquery</>
input using the new operators <literal>&lt;-&gt;</> and
<literal>&lt;<replaceable>N</>&gt;</literal>. The former means
that the lexemes before and after it must appear adjacent to
each other in that order. The latter means they must be exactly
<replaceable>N</> lexemes apart.
</para>
</listitem>
<listitem>
<!--
2016-03-04 [d78a7d9c7] Improve support of Hunspell in ispell dictionary.
2016-03-11 [8829af47e] Fix merge affixes for numeric ones
2016-03-17 [f4ceed6ce] Improve support of Hunspell