public inbox for [email protected]
help / color / mirror / Atom feedRe: Synchronizing slots from primary to standby
3+ messages / 3 participants
[nested] [flat]
* Re: Synchronizing slots from primary to standby
@ 2023-10-27 15:30 Drouvot, Bertrand <[email protected]>
2023-10-28 04:28 ` Re: Synchronizing slots from primary to standby Amit Kapila <[email protected]>
0 siblings, 1 reply; 3+ messages in thread
From: Drouvot, Bertrand @ 2023-10-27 15:30 UTC (permalink / raw)
To: Amit Kapila <[email protected]>; +Cc: shveta malik <[email protected]>; Peter Smith <[email protected]>; Hayato Kuroda (Fujitsu) <[email protected]>; Bharath Rupireddy <[email protected]>; Peter Eisentraut <[email protected]>; Bruce Momjian <[email protected]>; Ashutosh Sharma <[email protected]>; Andres Freund <[email protected]>; pgsql-hackers; Ajin Cherian <[email protected]>; Alvaro Herrera <[email protected]>
Hi,
On 10/27/23 10:35 AM, Amit Kapila wrote:
> On Wed, Oct 25, 2023 at 3:15 PM Drouvot, Bertrand
>
> I think even if we provide such an API, we need to have logic to get
> the slots from the primary and create them.
Yeah, my idea was to add an API (in addition to what is already in place).
> Say, even if the user used
> the APIs, there may still be some new slots that the sync worker needs
> to create.
Right.
> I think it might be better to provide a view for users to
> view the current state of sync. For example, in the above case, we can
> say "waiting for the primary to advance remote LSN" or something like
> that.
We are already displaying the wait event "ReplSlotsyncPrimaryCatchup" in pg_stat_activity
so that might already be enough?
My main idea was to be able to manually create/sync logical_slot2 in the test case described in [1]
without waiting for activity on logical_slot1.
But another (better?) option might be to change our current algorithm during slot creation on the
standby? (to avoid an "active" slot having to wait on a "inactive" one, like described in [1]).
[1]: https://www.postgresql.org/message-id/afe4ab6c-dde3-48ea-acd8-6f6052c7b8fd%40gmail.com
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Synchronizing slots from primary to standby
2023-10-27 15:30 Re: Synchronizing slots from primary to standby Drouvot, Bertrand <[email protected]>
@ 2023-10-28 04:28 ` Amit Kapila <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Amit Kapila @ 2023-10-28 04:28 UTC (permalink / raw)
To: Drouvot, Bertrand <[email protected]>; +Cc: shveta malik <[email protected]>; Peter Smith <[email protected]>; Hayato Kuroda (Fujitsu) <[email protected]>; Bharath Rupireddy <[email protected]>; Peter Eisentraut <[email protected]>; Bruce Momjian <[email protected]>; Ashutosh Sharma <[email protected]>; Andres Freund <[email protected]>; pgsql-hackers; Ajin Cherian <[email protected]>; Alvaro Herrera <[email protected]>
On Fri, Oct 27, 2023 at 9:00 PM Drouvot, Bertrand
<[email protected]> wrote:
>
> On 10/27/23 10:35 AM, Amit Kapila wrote:
> > On Wed, Oct 25, 2023 at 3:15 PM Drouvot, Bertrand
> >
> > I think even if we provide such an API, we need to have logic to get
> > the slots from the primary and create them.
>
> Yeah, my idea was to add an API (in addition to what is already in place).
>
> > Say, even if the user used
> > the APIs, there may still be some new slots that the sync worker needs
> > to create.
>
> Right.
>
> > I think it might be better to provide a view for users to
> > view the current state of sync. For example, in the above case, we can
> > say "waiting for the primary to advance remote LSN" or something like
> > that.
>
> We are already displaying the wait event "ReplSlotsyncPrimaryCatchup" in pg_stat_activity
> so that might already be enough?
>
I am fine if the wait is already displayed in some form.
> My main idea was to be able to manually create/sync logical_slot2 in the test case described in [1]
> without waiting for activity on logical_slot1.
>
> But another (better?) option might be to change our current algorithm during slot creation on the
> standby? (to avoid an "active" slot having to wait on a "inactive" one, like described in [1]).
>
Yeah, I guess it would be better to tweak the algorithm in this case
such that the slots can't be created immediately but can be noted in a
separate list and we can continue with other remaining slots. Once, we
are finished with all the slots, this special list can be traversed
and then we can attempt to create all the remaining slots. OTOH, the
scenario you described doesn't sound to be a frequent case to be
worried for it but if we can deal with it without adding much
complexity then it would be good.
--
With Regards,
Amit Kapila.
^ permalink raw reply [nested|flat] 3+ messages in thread
* [PATCH v18 6/8] Row pattern recognition patch (docs).
@ 2024-05-11 07:11 Tatsuo Ishii <[email protected]>
0 siblings, 0 replies; 3+ messages in thread
From: Tatsuo Ishii @ 2024-05-11 07:11 UTC (permalink / raw)
---
doc/src/sgml/advanced.sgml | 82 ++++++++++++++++++++++++++++++++++++
doc/src/sgml/func.sgml | 54 ++++++++++++++++++++++++
doc/src/sgml/ref/select.sgml | 38 ++++++++++++++++-
3 files changed, 172 insertions(+), 2 deletions(-)
diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml
index 755c9f1485..b0b1d1c51e 100644
--- a/doc/src/sgml/advanced.sgml
+++ b/doc/src/sgml/advanced.sgml
@@ -537,6 +537,88 @@ WHERE pos < 3;
<literal>rank</literal> less than 3.
</para>
+ <para>
+ Row pattern common syntax can be used to perform row pattern recognition
+ in a query. The row pattern common syntax includes two sub
+ clauses: <literal>DEFINE</literal>
+ and <literal>PATTERN</literal>. <literal>DEFINE</literal> defines
+ definition variables along with an expression. The expression must be a
+ logical expression, which means it must
+ return <literal>TRUE</literal>, <literal>FALSE</literal>
+ or <literal>NULL</literal>. The expression may comprise column references
+ and functions. Window functions, aggregate functions and subqueries are
+ not allowed. An example of <literal>DEFINE</literal> is as follows.
+
+<programlisting>
+DEFINE
+ LOWPRICE AS price <= 100,
+ UP AS price > PREV(price),
+ DOWN AS price < PREV(price)
+</programlisting>
+
+ Note that <function>PREV</function> returns the price column in the
+ previous row if it's called in a context of row pattern recognition. Thus in
+ the second line the definition variable "UP" is <literal>TRUE</literal>
+ when the price column in the current row is greater than the price column
+ in the previous row. Likewise, "DOWN" is <literal>TRUE</literal> when when
+ the price column in the current row is lower than the price column in the
+ previous row.
+ </para>
+ <para>
+ Once <literal>DEFINE</literal> exists, <literal>PATTERN</literal> can be
+ used. <literal>PATTERN</literal> defines a sequence of rows that satisfies
+ certain conditions. For example following <literal>PATTERN</literal>
+ defines that a row starts with the condition "LOWPRICE", then one or more
+ rows satisfy "UP" and finally one or more rows satisfy "DOWN". Note that
+ "+" means one or more matches. Also you can use "*", which means zero or
+ more matches. If a sequence of rows which satisfies the PATTERN is found,
+ in the starting row of the sequence of rows all window functions and
+ aggregates are shown in the target list. Note that aggregations only look
+ into the matched rows, rather than whole frame. On the second or
+ subsequent rows all window functions are NULL. Aggregates are NULL or 0
+ (count case) depending on its aggregation definition. For rows that do not
+ match on the PATTERN, all window functions and aggregates are shown AS
+ NULL too, except count showing 0. This is because the rows do not match,
+ thus they are in an empty frame. Example of a <literal>SELECT</literal>
+ using the <literal>DEFINE</literal> and <literal>PATTERN</literal> clause
+ is as follows.
+
+<programlisting>
+SELECT company, tdate, price,
+ first_value(price) OVER w,
+ max(price) OVER w,
+ count(price) OVER w
+FROM stock
+ WINDOW w AS (
+ PARTITION BY company
+ ORDER BY tdate
+ ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING
+ AFTER MATCH SKIP PAST LAST ROW
+ INITIAL
+ PATTERN (LOWPRICE UP+ DOWN+)
+ DEFINE
+ LOWPRICE AS price <= 100,
+ UP AS price > PREV(price),
+ DOWN AS price < PREV(price)
+);
+</programlisting>
+<screen>
+ company | tdate | price | first_value | max | count
+----------+------------+-------+-------------+-----+-------
+ company1 | 2023-07-01 | 100 | 100 | 200 | 4
+ company1 | 2023-07-02 | 200 | | | 0
+ company1 | 2023-07-03 | 150 | | | 0
+ company1 | 2023-07-04 | 140 | | | 0
+ company1 | 2023-07-05 | 150 | | | 0
+ company1 | 2023-07-06 | 90 | 90 | 130 | 4
+ company1 | 2023-07-07 | 110 | | | 0
+ company1 | 2023-07-08 | 130 | | | 0
+ company1 | 2023-07-09 | 120 | | | 0
+ company1 | 2023-07-10 | 130 | | | 0
+(10 rows)
+</screen>
+ </para>
+
<para>
When a query involves multiple window functions, it is possible to write
out each one with a separate <literal>OVER</literal> clause, but this is
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 17c44bc338..8dbab31300 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -23124,6 +23124,7 @@ SELECT count(*) FROM sometable;
returns <literal>NULL</literal> if there is no such row.
</para></entry>
</row>
+
</tbody>
</tgroup>
</table>
@@ -23163,6 +23164,59 @@ SELECT count(*) FROM sometable;
Other frame specifications can be used to obtain other effects.
</para>
+ <para>
+ Row pattern recognition navigation functions are listed in
+ <xref linkend="functions-rpr-navigation-table"/>. These functions
+ can be used to describe DEFINE clause of Row pattern recognition.
+ </para>
+
+ <table id="functions-rpr-navigation-table">
+ <title>Row Pattern Navigation Functions</title>
+ <tgroup cols="1">
+ <thead>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ Function
+ </para>
+ <para>
+ Description
+ </para></entry>
+ </row>
+ </thead>
+
+ <tbody>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>prev</primary>
+ </indexterm>
+ <function>prev</function> ( <parameter>value</parameter> <type>anyelement</type> )
+ <returnvalue>anyelement</returnvalue>
+ </para>
+ <para>
+ Returns the column value at the previous row;
+ returns NULL if there is no previous row in the window frame.
+ </para></entry>
+ </row>
+
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>next</primary>
+ </indexterm>
+ <function>next</function> ( <parameter>value</parameter> <type>anyelement</type> )
+ <returnvalue>anyelement</returnvalue>
+ </para>
+ <para>
+ Returns the column value at the next row;
+ returns NULL if there is no next row in the window frame.
+ </para></entry>
+ </row>
+
+ </tbody>
+ </tgroup>
+ </table>
+
<note>
<para>
The SQL standard defines a <literal>RESPECT NULLS</literal> or
diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml
index 066aed44e6..8f18718d58 100644
--- a/doc/src/sgml/ref/select.sgml
+++ b/doc/src/sgml/ref/select.sgml
@@ -969,8 +969,8 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl
The <replaceable class="parameter">frame_clause</replaceable> can be one of
<synopsis>
-{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
-{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ]
+{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax]
+{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax]
</synopsis>
where <replaceable>frame_start</replaceable>
@@ -1077,6 +1077,40 @@ EXCLUDE NO OTHERS
a given peer group will be in the frame or excluded from it.
</para>
+ <para>
+ The
+ optional <replaceable class="parameter">row_pattern_common_syntax</replaceable>
+ defines the <firstterm>row pattern recognition condition</firstterm> for
+ this
+ window. <replaceable class="parameter">row_pattern_common_syntax</replaceable>
+ includes following subclauses. <literal>AFTER MATCH SKIP PAST LAST
+ ROW</literal> or <literal>AFTER MATCH SKIP TO NEXT ROW</literal> controls
+ how to proceed to next row position after a match
+ found. With <literal>AFTER MATCH SKIP PAST LAST ROW</literal> (the
+ default) next row position is next to the last row of previous match. On
+ the other hand, with <literal>AFTER MATCH SKIP TO NEXT ROW</literal> next
+ row position is always next to the last row of previous
+ match. <literal>DEFINE</literal> defines definition variables along with a
+ boolean expression. <literal>PATTERN</literal> defines a sequence of rows
+ that satisfies certain conditions using variables defined
+ in <literal>DEFINE</literal> clause. If the variable is not defined in
+ the <literal>DEFINE</literal> clause, it is implicitly assumed
+ following is defined in the <literal>DEFINE</literal> clause.
+
+<synopsis>
+<literal>variable_name</literal> AS TRUE
+</synopsis>
+
+ Note that the maximu number of variables defined
+ in <literal>DEFINE</literal> clause is 26.
+
+<synopsis>
+[ AFTER MATCH SKIP PAST LAST ROW | AFTER MATCH SKIP TO NEXT ROW ]
+PATTERN <replaceable class="parameter">pattern_variable_name</replaceable>[+] [, ...]
+DEFINE <replaceable class="parameter">definition_varible_name</replaceable> AS <replaceable class="parameter">expression</replaceable> [, ...]
+</synopsis>
+ </para>
+
<para>
The purpose of a <literal>WINDOW</literal> clause is to specify the
behavior of <firstterm>window functions</firstterm> appearing in the query's
--
2.25.1
----Next_Part(Sat_May_11_16_23_07_2024_789)--
Content-Type: Text/X-Patch; charset=us-ascii
Content-Transfer-Encoding: 7bit
Content-Disposition: inline;
filename="v18-0007-Row-pattern-recognition-patch-tests.patch"
^ permalink raw reply [nested|flat] 3+ messages in thread
end of thread, other threads:[~2024-05-11 07:11 UTC | newest]
Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed)
-- links below jump to the message on this page --
2023-10-27 15:30 Re: Synchronizing slots from primary to standby Drouvot, Bertrand <[email protected]>
2023-10-28 04:28 ` Amit Kapila <[email protected]>
2024-05-11 07:11 [PATCH v18 6/8] Row pattern recognition patch (docs). Tatsuo Ishii <[email protected]>
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox