Reduce Count(*) time in Postgres for Many Records


EXPLAIN ANALYZE select count(*) from product; 

ROWS: 534965


Finalize Aggregate  (cost=53840.85..53840.86 rows=1 width=8) (actual time=5014.774..5014.774 rows=1 loops=1)   ->  Gather  (cost=53840.64..53840.85 rows=2 width=8) (actual time=5011.623..5015.480 rows=3 loops=1)         Workers Planned: 2         Workers Launched: 2         ->  Partial Aggregate  (cost=52840.64..52840.65 rows=1 width=8) (actual time=4951.366..4951.367 rows=1 loops=3)               ->  Parallel Seq Scan on product prod  (cost=0.00..52296.71 rows=217571 width=0) (actual time=0.511..4906.569 rows=178088 loops=3) Planning Time: 34.814 ms Execution Time: 5015.580 ms 

How can we optimize the above query to get the counts very quickly?

This is a simple query, however, its variations can include different conditions and join with other tables.

I want to use the output of Solve and/or Reduce in next steps. But the output comes in the form of a rule [duplicate]

In a program I want to use the output of Solve and/or Reduce in next steps. But the output comes in the form of a rule, where what I want is the numerical solution. Here is an example. Say I write s=Solve[x+2==5,x]. In the next step I want to use this solution, so I write: y=2 s +3. This returns {{3+2(x->3)}}. This is a very basic need, but hours combing through the documentation leads nowhere.

Using output from Solve or Reduce as a value in subsequent equation

I’m trying to run a simulation. I will number sentences to make response easier. (1) Here is my first equation:

๐‘—[LBar_, y_, x1_, ฯƒ_, X2M_, w_, X1M_]:=(LBar(๐œŽโˆ’1)โ„๐œŽ + ๐‘ฆ(๐œŽโˆ’1)โ„๐œŽโˆ’x1(๐œŽโˆ’1)โ„๐œŽ)๐œŽโ„(๐œŽโˆ’1)โˆ’(๐‘ฆโˆ’X2M+๐‘ค(LBar+X1M)โˆ’๐‘คx1) 

(2) I insert some parameter values and Reduce:

Reduce[๐œ•x1(๐‘—[100,๐‘ฆ,x1,13โ„,42,.23,80])==0 && x1>0, x1, Reals] 

(3) This produces output:

x1 == 119.575 

(4) When I try to call the output value (119.575) I run into problems. (5) For instance

2 % 

results in:

2 (x1 == 119.575) 

(6) and

j[100, 80, %[[2]], 1/3, 42, .23, 80] 

produces this output:

-79.4 + 1/Sqrt[41/160000 - 1/239.149[[2]]^2] + 0.23 239.149[[2]] 

a way to reduce amount of times it checks emails ?

is there a way to a way to reduce the amount of times it checks emails ?

i have changed the “login intervals” from 900 seconds to 1800 seconds,

under “email verification”  “time to wait between 2 logins”

and ticked “per account (else pop3 server)”

i wanted to reduce the amount of times it was logging in to check the emails to increase performance,
as well i was getting loads of errors such as –

“pop3 login failed sock error connection timed out”
“pop3 login failed sock error host not found”

but its still bringing loads of messages “skipped email checking”
how to take these off as well to improve performance ?

MySQL Transform multiple rows into a single row in same table (reduce by merge group by)

Hy, i want reduce my table and updating himself (group and sum some columns, and delete rows)

Source table "table_test" :

+----+-----+-------+----------------+ | id | qty | user  | isNeedGrouping | +----+-----+-------+----------------+ |  1 |   2 | userA |              1 | <- row to group + user A |  2 |   3 | userB |              0 | |  3 |   5 | userA |              0 | |  4 |  30 | userA |              1 | <- row to group + user A |  5 |   8 | userA |              1 | <- row to group + user A |  6 |   6 | userA |              0 | +----+-----+-------+----------------+ 

Wanted table : (Obtained by)

DROP TABLE table_test_grouped; SET @increment = 2; CREATE TABLE table_test_grouped SELECT id, SUM(qty) AS qty, user, isNeedGrouping FROM table_test GROUP BY user, IF(isNeedGrouping = 1, isNeedGrouping, @increment := @increment + 1); SELECT * FROM table_test_grouped;  +----+------+-------+----------------+ | id | qty  | user  | isNeedGrouping | +----+------+-------+----------------+ |  1 |   40 | userA |              1 | <- rows grouped + user A |  3 |    5 | userA |              0 | |  6 |    6 | userA |              0 | |  2 |    3 | userB |              0 | +----+------+-------+----------------+ 

Problem : i can use another (temporary) table, but i want update initial table, for :

  • grouping by user and sum qty
  • replace/merge rows into only one by group

The result must be a reduce of initial table, group by user, and qty summed.

And it’s a minimal exemple, and i don’t want full replace inital from table_test_grouped, beacause in my case, i have another colum (isNeedGrouping) for decide if y group or not.

For flagged rows "isNeedGrouping", i need grouping. For this exemple, a way to do is sequentialy to :

CREATE TABLE table_test_grouped SELECT id, SUM(qty) AS qty, user, isNeedGrouping FROM table_test WHERE isNeedGrouping = 1 GROUP BY user ; DELETE FROM table_test WHERE isNeedGrouping = 1 ; INSERT INTO table_test SELECT * FROM table_test_grouped ; 

Any suggestion for a simpler way?

Are there any attacks or effects that reduce max HP to 0 without stating what happens?

Inspired by PJRZ’s comment on this answer to this question:

What attacks actually exist that reduce someone’s max HP, but do not specifically state what happens at max HP of 0?

As far as I am aware, all monster abilities that can reduce max HP to 0 state that the creature dies (and optionally may be brought back as some undead creature, depending on the exact creature/attack used to reduce the max HP to 0).

As an example of an attack that does state what happens, consider a Wraith’s Life Drain attack (MM, pg. 302):

Life Drain. Melee Weapon Attack: +6 to hit, reach 5 ft., one creature. Hit: 21 (4d8 + 3) necrotic damage. The target must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Are there any attacks or effect that reduce a creature’s max HP to 0, but do not address whether or not the target dies?

How can a low level rouge reduce a targets constitution bonus

I want to play a rogue that relies heavily on poisons and other utility flasks (ie: alchemists fire). We’re starting out at level 1 and the story arc should take us to roughly level 11. To make poisons more reliable, how would you go about reducing a targets constitution so that there is a better chance that the target has a better chance at failing their saving roll?

In Battle? Out of Battle?

Identified Folder does not reduce in size over time

Hi @Sven

I am trying to figure out how to exhaust my identified folder to make it all verified (how to find more verified faster).

When I monitored over last 2 days, with a project that only uses Identified links, these are my folder sizes:

Day 0 
Identified 494mb
Submitted 549mb
Verified 829mb

Day 2
Identified 511mb
Submitted 572mb
Verified 857mb

My expectation would be the Identified folder reduces in size as  links are deleted from this folder when they are submitted/verified, however the Identified folder is increasing in size instead??

Am I missing something?

Can Magical Lineage reduce a spell’s level multiple times?

Oh wise brains of the internet, I implore thee

Magical Lineage states "Pick one spell when you choose this trait. When you apply metamagic feats to this spell that add at least 1 level to the spell, treat its actual level as 1 lower for determining the spellโ€™s final adjusted level."

If applying multiple metamagic feats to a spell, such as Maximized + Empowered, would Magical Lineage reduce the total adjusted level by 2 (once for each application of a metamagic feat) or only once regardless of the number of metamagic feats?

My initial take is that it only applies once, regardless of the number of metamagic feats applied, but might as well double check and make sure it’s right.

I just want to know whether I should be preparing Maximized Empowered Battering Blast into a 7th level slot or a 6th level slot.

Thank you.