Stack Overflow
Stack Overflow

Questions tagged [postgresql-parallel-query]

Parallel Query in PostgreSQL enables multiple threads working on the same table for the same query in parallel.

Parallel Query is a feature of PostgreSQL 9.6 or later. It uses query plans leveraging multiple CPUs in order to answer queries faster. Only applicable for certain types of queries. Queries that touch a large amount of data but return only a few rows to the user will typically benefit most. Like SELECT COUNT(*) FROM tbl.
There are some important limitations.

Resources
14 questions
5
votes
1 answer

Postgres 9.6 parallel XPath

I've set up Postgres 9.6 and checked on a large table of random integers that parallel queries are working. However, a simple XPath query on an XML column of another table is always sequential. Both XPath functions are marked as parallel safe in…
Eugene Pakhomov
  • 9,309
  • 3
  • 27
  • 53
5
votes
0 answers

Parallel queries on CTE for writing operations in PostgreSQL

From PostgreSQL 9.6 Release Notes: Only strictly read-only queries where the driving table is accessed via a sequential scan can be parallelized. My question is: If a CTE (WITH clause) contains only read operations, but its results is used to feed…
bitifet
  • 3,514
  • 15
  • 37
3
votes
2 answers

To what degree does PostgreSQL support parallel DDL?

Looking here, it is clear that Oracle supports execution of DDL commands in parallel with scenarios clearly listed. I was wondering whether Postgres does indeed offer such functionality? I can find a lot of material on "parallel queries" for…
Zeruno
  • 1,391
  • 2
  • 20
  • 39
3
votes
1 answer

Does PostgreSQL query partitions in parallel?

Postgres now has parallel queries. Are parallel queries used when the table is partitioned, the query is on the master table, and more than one partitions (child tables) are involved. For example, I partition by the hour of the day. Then I want to…
rwfbc
  • 900
  • 1
  • 10
  • 22
2
votes
2 answers

Understanding how many parallel workers remain from a worker pool across sessions for PostgreSQL parallel queries?

Let's say I have a pool of 4 parallel workers in my PostgreSQL database configuration. I also have 2 sessions. In session#1, the SQL is currently executing, with my planner randomly choosing to launch 2 workers for this query. So, in session#2, how…
baceda9220
  • 41
  • 1
  • 4
2
votes
1 answer

Concurrent queries in PostgreSQL - what is actually happening?

Let us say we have two users running a query against the same table in PostgreSQL. So, User 1: SELECT * FROM table WHERE year = '2020' and User 2: SELECT * FROM table WHERE year = '2019' Are they going to be executed at the same time as opposed to…
Zeruno
  • 1,391
  • 2
  • 20
  • 39
1
vote
1 answer

Query stops parallelizing when adding LIMIT or ROW_NUMBER

I have 20 tables with identical structure, and I need to aggregate the results. I'm using UNION ALL to collect the results, in the following structure: SELECT something, SUM(total) AS overall_total FROM ( SELECT something, SUM(something_else) AS…
WhatMeWorry
  • 11
  • 1
1
vote
1 answer

Optimizing SELECT count(*) on large table

Basic count on a large table on PostgreSQL 14 with 64GB Ram & 20 threads. Storage is an NVME disk. Questions: How do I improve the query for this select count query? What kind of optimizations should I look into on Postgres configuration? The…
CodeGuru
  • 3,645
  • 14
  • 55
  • 99
1
vote
1 answer

Materialized view refresh in parallel

Created materialized view in parallel by setting max_parallel_workers_per_gather to 4. I could see parallel sessions kicking off and creating the mview much faster than serial execution (10mins - parallel vs over an hour - serial). Now I want the…
nmakb
  • 1,069
  • 1
  • 17
  • 35
1
vote
2 answers

Postgres, is query performance depending on front-end tool?

I was trying the same query select column_1, count(1) from table group by 1 order by 1 desc with several front-end tools, and I was getting very different results.(I ran query several time to avoid anomalies or cashing issues) I always thought…
Baker
  • 425
  • 1
  • 7
  • 20
0
votes
1 answer

Postgresql 15 query optimizer refuses to parallelize a query on a partitioned table

I have a table "weather" that stores weather parameters for 45 years of entire Europe area with 400 million of record partitioned by range in an Oracle database managed through 19c instance and the table has been duplicated using oracle_fdw foreign…
Tony Zucchini
  • 11
  • 3
0
votes
1 answer

Is it possible to execute parallel query in Postgres which queries partitioned table by using union all?

Hello I'm playing around with postgres as a search engine by using GIN indexes with trigram module and partitioned table and I'm trying to parallelize the query but no matter what I set the query is always sequential any ideas are welcome. Check out…
Kamil Szulc
  • 33
  • 4
0
votes
1 answer

PostgreSQL parallel queries using SPI possible?

I am using PostgreSQL's Server Programming Interface (SPI) to build my postgres extension and execute my query. Please see this detailed example, or the following simple code sample: int ret = SPI_exec("SELECT * FROM ....", 0); We know that…
Zeruno
  • 1,391
  • 2
  • 20
  • 39
0
votes
0 answers

Postgres does not apply parallel query

I am using "PostgreSQL 11.4, compiled by Visual C++ build 1914, 64-bit" I want to run parallel query for testing purpose, below is my pg_settings parameter values: "checkpoint_completion_target" >> "0.5" "default_statistics_target" >>…
Abdullah-Al Roman
  • 11
  • 1