postgresql

Rafia Sabih: Using parallel sequential scan in PostgreSQL

planet postgresql - 2018-10-31(水) 22:29:00
Parallel sequential scan is the first parallel access method in PostgreSQL and is introduced in version 9.6.  The committer of this feature and my colleague at EnterpriseDB Robert Haas wrote an awesome blog on it, there is another great blog by another PostgreSQL committer and my colleague Amit Kapila. Both of these blogs explain this access method, its design, usage, and related parameters. 
Still, I could not help but notice that there are curiosities around the usage of this access method. Every now and then I could see a complaint saying parallel sequential scan is not getting selected or it is degrading the performance of a query.  So, I decided to write this blog to cater more practical scenarios and specifically focus on its less talked about aspect  -- where parallel sequential scan would (should) not improve the performance.
Before diving into the details of parallel SeqScan, let's first understand the basic infrastructure and terminology related to it in PostgreSQL. The processes that run in parallel and scan the tuples of a relation are called parallel workers or workers in short. There is one special worker namely leader which co-ordinates and collects the output of the scan from each  of the worker. This worker may or may not participate in scanning the relation depending on it's load in dividing and combining processes. End users can also control the involvement of leader in relation scan by GUC parameter parallel_leader_participation, it is a boolean parameter. 
Now, let's understand the concept of parallel scan in PostgreSQL by a simple example.
  • Let there be a table T (a int, b int) containing 100 tuples
  • Let's say we have two workers and one leader,
  • Cost of scanning one tuple is 10
  • Cost of communicating a tuple from worker to leader is 20
  • Cost of dividing the tuples among workers is 30
  • For simplicity, let's assume that leader gives 50 tuples to each of the worker
Now, let's analyse if parallel scan will be faster than non parallel scan,
Cost of SeqScan = 10*100 = 1000
Cost of Parallel SeqSc[...]
カテゴリー: postgresql

Liaqat Andrabi: Webinar: PostgreSQL is NOT your traditional SQL database [Follow Up]

planet postgresql - 2018-10-31(水) 16:00:58

PostgreSQL is referred to as “The world’s most advanced open source database” – but what does PostgreSQL have that other open source relational databases don’t?  

2ndQuadrant recently hosted a webinar on this very topic: PostgreSQL is NOT your traditional SQL database, presented by Gülçin Yıldırım Jelínek, Cloud Services Manager at 2ndQuadrant.

The recording of the webinar is now available here.

Questions that Gülçin couldn’t respond to during the live webinar have been answered below.

Q1: What exactly is the role of postgresql for a marketplace like ebay or rakuten?

A1: This question is not very clear. If the question is about whether Postgres can be used in an e-commerce website, the answer is yes.

 

Q2: I’m in process of switching from MS SQL Server to Postgres and I have an issue:
Simple search in text columns with diacritics chart.

Ex: table Person
Name
——-
Ștefan
ștefan
Stefan

When I search:

SELECT * FROM pers WHERE Name LIKE 'ste%';

I want to retrieve all records from above.
In SQL Server there’s a simple way to accomplish this – I use: COLLATE Latin1_General_100_CI_AI when I define column, and that it’s.
Do you have recommendations to accomplish the same task in Postgres?

A2: The unaccenting collations are not supported in PostgreSQL. You can query like this to get the same result:

SELECT * FROM pers WHERE unaccent(Name) ILIKE 'ste%';


For any questions, comments, or feedback, please visit our website or send an email to webinar@2ndquadrant.com.

カテゴリー: postgresql

Quinn Weaver: Remember your history

planet postgresql - 2018-10-31(水) 14:56:00
PostgreSQL keeps track of which WAL files go with which timelines in small history files. Each time you make a base backup, a history file is born. The file is written once and never updated. It's a simple system, and it works well and silently.

In fact, sometimes it works a little too silently.

At PostgreSQL Experts we've run into the problem where a client's history files disappear because they are stored in S3, and there's a lifecycle configuration in place that says to move everything over a certain age to Glacier. That's a good policy for WAL files!

Unfortunately, it's not a good policy for history files: without the latest history file you can't restore the latest backup, and without past history files, you are unable to do PITR to certain points in time.

The solution we used was to move the whole WAL archive to S3 Standard-Infrequent Access storage, dissolving the problem with lifecycle configurations while controlling costs. But you could also fix this by editing the lifecycle configuration.

The important thing is this: hold on to all history files. They're tiny text files, and when you need them, you really need them. This is also a good reason to test restores, not just of the latest backup, but of database states at arbitrary points in time.

*    *    *
Addendum: another very common problem we see is WAL archives that become corrupted because a client accidentally pointed a two primaries at the same WAL archive (for instance, they might have copied a postgresql.conf file by hand, or via a DevOps tool like Puppet). In this case, the whole archive is corrupted, and you're best off starting with a fresh S3 bucket or an empty directory and doing a new base backup immediately.

One of the many nice features of pgBackRest is that it will notice this and prevent you from doing it. Fewer footguns → better backups.
カテゴリー: postgresql

Hubert 'depesz' Lubaczewski: Foreign Key to partitioned table – part 2

planet postgresql - 2018-10-31(水) 10:45:14
Previously I wrote about how to create foreign key pointing to partitioned table. Final solution in there required four separate functions and four triggers for each key between two tables. Let's see how fast it is, and if it's possible to make it simpler. First bit – performance test (for making it simpler you will … Continue reading "Foreign Key to partitioned table – part 2"
カテゴリー: postgresql

Luca Ferrari: pgenv gets patching support

planet postgresql - 2018-10-31(水) 09:00:00

pgenv does now support a customizable patching feature that allows the user to define which patches to apply when an instance is built.

pgenv gets patching support

pgenv, the useful tool for managing several PostgreSQL installations, gets support for customizable patching.

What is all about? Well, it happens that you could need to patch PostgreSQL source tree before you build, and it could be because something on your operating system is different than the majority of the systems PostgreSQL is built against. Nevermind, you need to patch it!

pgenv did support a very simple patching mechanism hardcoded within the program itself, but during the last days I worked on a different and more customizable approach. The idea is simple: the program will apply every patch file listed in an index for the particular version. So, if you want to build the outshining 11.0 and need to patch it, build an index text file and list there all the patches, and the pgenv build process will apply them before compiling.

Of course, what if you need to apply the same patches over and over to different versions? You will end up with several indexes, one for each version you need to patch. Uhm…not so smart! To avoid this, I designed the patching index selection in a way that allows you to group patches for operating system and brand.

Allow me to explain more in detail with an example. Suppose you are on a Linux machine and need to patch version 11.0: the program will search for a file that matches any of the following:

$PGENV_ROOT/patch/index/patch.11.0.Linux $PGENV_ROOT/patch/index/patch.11.0 $PGENV_ROOT/patch/index/patch.11.Linux $PGENV_ROOT/patch/index/patch.11

This desperate searching for works selecting the first file that matches the operating system and PostgreSQL version or a combination of the two...

カテゴリー: postgresql

Hubert 'depesz' Lubaczewski: Waiting for PostgreSQL 12 – Add pg_partition_tree to display information about partitions

planet postgresql - 2018-10-31(水) 05:33:03
On 30th of October 2018, Michael Paquier committed patch: Add pg_partition_tree to display information about partitions     This new function is useful to display a full tree of partitions with a partitioned table given in output, and avoids the need of any complex WITH RECURSIVE query when looking at partition trees which are deep … Continue reading "Waiting for PostgreSQL 12 – Add pg_partition_tree to display information about partitions"
カテゴリー: postgresql

Nickolay Ihalainen: PostgreSQL locking, part 3: lightweight locks

planet postgresql - 2018-10-30(火) 22:31:40

PostgreSQL lightweight locks, or LWLocks, control memory access. PostgreSQL uses multi-process architecture and should allow only consistent reads and writes to shared memory structures. LWLocks have two levels of locking: shared and exclusive. It’s also possible to release all acquired LWLocks to simplify clean up. Other databases often call primitives similar to LWLocks “latches”. Because LWLocks is an implementation detail, application developers shouldn’t pay much attention to this kind of locking.

This is the third and final part of a series on PostgreSQL locking, related to latches protecting internal database structures. Here are the previous parts: Row-level locks and table-level locks.

Instrumentation

Starting from PostgreSQL 9.6, LWLocks activity can be investigated with the pg_stat_activity system view. It could be useful under high CPU utilization. There are system settings to help with contention on specific lightweight locks.

Before PostgreSQL 9.5, the LWLocks implementation used spin-locks.  It was a bottleneck. This was fixed in 9.5 with atomic state variable.

Potential heavy contention places
  • WALInsertLock: protects WAL buffers. You can increase the number of wal buffers to get a slight improvement. Incidentally, synchronous_commit=off increases pressure on the lock even more, but it’s not a bad thing. full_page_writes=off reduces contention, but it’s generally not recommended.
  • WALWriteLock: accrued by PostgreSQL processes while WAL records are flushed to disk or during a WAL segments switch. synchronous_commit=off removes the wait for disk flush, full_page_writes=off reduces the amount of data to flush.
  • LockMgrLock: appears in top waits during a read-only workload. It latches relations regardless of its size. It’s not a single lock, but at least 16 partitions. Thus it’s important to use multiple tables during benchmarks and avoid single table anti-pattern in production.
  • ProcArrayLock: Protects the ProcArray structure. Before PostgreSQL 9.0, every transaction acquired this lock exclusively befo
[...]
カテゴリー: postgresql

Craig Kerstiens: The biggest mistake Postgres ever made

planet postgresql - 2018-10-30(火) 22:30:34

Postgres has experienced a long and great run. It’s over 20 years old and has a track record of being safe and reliable (which is the top thing I care about in a database). In recent years it’s become more cool with things like JSONB, JIT support, and a powerful extension ecosystem. But, Postgres has made some mistakes along the way, the most notable being it’s name.

Postgres gets its name from Ingress. Ingress was one of the first databases and was lead by Michael Stonebreaker who won a Turing award for Postgres and other works. Ingress began in the early 70s at UC Berkeley, which is still to this day known as a top university when it comes to databases. Out of Ingress came a number of databases you’ll still know today such as SQL Server and Sybase. It also as you may have guessed by now spawned Postgres which means Post-Ingress.

In the early days of Postgres there was no SQL. No not NoSQL, there was not SQL. Postgres had it’s own query language. It wasn’t until 1995 that Postgres received SQL support, and with its addition of SQL support it updated it’s name to PostgreSQL.

You see, with Postgres becoming PostgreSQL we began a journey of Postgres being mispronounced for it’s forseeable future and it is still currently the case. Is it really that big of an issue? Well it’s big enough that the PostgreSQL website has a FAQ including “How to pronounce PostgreSQL”. As it stands today there are two generally accepted names:

  • post-GRES-que-ell
  • Postgres

With one of the above there is far less confusion. And in fact I’m not the only one to share this opinion. Tom Lane is a major contributor to every Postgres release for more than the last decade. He’s one of the top 10 contributors to open source in general having worked on the JPEG/PNG/TIFF image formats before coming over to database land. Tom has this classic email in the PostgreSQL mailing list:

```

[>> Can i get data in postgre from non-postgre db? > The name is PostgreSQL or Postgres, not postgre. It might help to explain that the pronunciation is "post-g[...]
カテゴリー: postgresql

Hubert 'depesz' Lubaczewski: Waiting for PostgreSQL 12 – Add pg_promote function

planet postgresql - 2018-10-30(火) 22:08:49
On 25th of October 2018, Michael Paquier committed patch: Add pg_promote function     This function is able to promote a standby with this new SQL-callable function. Execution access can be granted to non-superusers so that failover tools can observe the principle of least privilege.   Catalog version is bumped.   Author: Laurenz Albe   … Continue reading "Waiting for PostgreSQL 12 – Add pg_promote function"
カテゴリー: postgresql

Kaarel Moppel: Peeking at query performance of the upcoming version 11 of PostgreSQL

planet postgresql - 2018-10-30(火) 18:00:25

Last weeks the first release candidate of the upcoming Postgres version 11 was released, stating that everything is going more or less as planned – great news! The 11 release is promising a lot of very cool stuff as usual, including – better partitioning, more parallization and JIT capabilities (which are not activated by default though). Besides those headline features there of course hundreds or rather thousands (`git diff –shortstat REL_10_5..REL_11_RC1` says “3192 files changed, 324206 insertions, 178499 deletions”) of smaller changes with some of them for sure boosting performance also on some typical queries. Release notes didn’t state any numerical performance indicators though as usually, so people have to find it out on their own – so that’s what this blog post is about. I’m basically running 4 quite simple analytical/aggregate type of queries and laying out the numbers for you to evaluate – so jump to the summarizing table end of the post or get into the details by reading on.

Test Queries

3 out of 4 test queries I actually just carried over from the last year’s similar test for 9.6 vs 10 (check it out here if you’re into archeology) and added one query to test index traversing performance. Queries are all tied to the schema generated by our good old friend pgbench, with one minor adjustment – creating a copy of the pgbench_accounts table be able to simulate a join on two 1 million rows tables. This time I also didn’t disable the parallel features as they’re “on” by default for both versions and thus won’t be probably touched for most setups.

/* Sum up 50mio rows */ SELECT sum(abalance) FROM pgbench_accounts CROSS JOIN generate_series(1, 5) /* Unique columns joining */ SELECT count(*) FROM pgbench_accounts JOIN pgbench_accounts_copy using (aid) /* Using Grouping Sets analytical feature */ SELECT count(*) FROM (SELECT aid, bid, count(*) FROM pgbench_accounts GROUP BY CUBE (aid, bid)) a; /* B-tree index traversing */ SELECT COUNT(DISTINCT aid) FROM pgbench_accounts where aid % 2 = 0;

For pbench “sc

[...]
カテゴリー: postgresql

Quinn Weaver: It's just an expression

planet postgresql - 2018-10-30(火) 15:23:00
PostgreSQL has lots of great features for text search.

In particular, there are a bunch of ways to do case-insensitive searches for text:
  • There's standard SQL ILIKE… but than can be expensive — especially if you put %'s at both start and end — and it's overkill if you want an exact string match.
  • The same goes for case-insensitive regexp matching: overkill for simple case-insensitive matches. It does work with indexes, though!
  • Then there's the citext extension, which is pretty much the perfect answer. It lets you use indexes and still get case-insensitive matching, which is really cool. It Just Works.
OK, but what if you didn't have the foresight to use citext? And what if you don't want to go through the pain of changing the data type of that column? In a case like this, an expression index can be really handy.

Without an index, a case-insensitive match like this can be quite expensive indeed:
sandbox# select addy from email_addresses where lower(addy) = 'quinn@example.com';

                                               QUERY PLAN
----------------------------------------------------------------------------------------------------------
 Seq Scan on email_addresses  (cost=0.00..1.04 rows=1 width=32) (actual time=0.031..0.032 rows=1 loops=1)
   Filter: (lower(addy) = 'quinn@example.com'::text)
   Rows Removed by Filter: 3
 Planning time: 0.087 ms
 Execution time: 0.051 ms
(5 rows)

(That's a sequential scan of the entire table, lowercasing the addy column of each row before comparing it to the desired address.)

And a regular index on email_addresses(addy) won't help, because the lower() operation forces a sequential scan.
But an expression index will do the trick:

sandbox# create index email_addresses__lower__addy on email_addresses (lower(addy));
CREATE INDEX
sandbox# explain analyze select addy from email_addresses where lower(addy) = 'quinn@example.com';
                                                                  QUERY PLAN
------------------------------------------------------------------------[...]
カテゴリー: postgresql

damien clochard: Introducing PostgreSQL Anonymizer

planet postgresql - 2018-10-29(月) 19:17:36

I’ve just released today an extension called PostgreSQL Anonymizer that will mask or replace personally identifiable information (PII) or commercially sensitive data from a PostgreSQL database.

The project is open source and available here :

https://gitlab.com/daamien/postgresql_anonymizer

I strongly believe in a declarative approach of anonymization : the location of sensitive information inside database and the rules to hide this information should be declared directly using the Data Definition Language (DDL). In the age of GDPR, developpers should specify an anonymization strategy inside the table definitions, just like they specify data types, foreign keys and constraints.

This project is a prototype designed to show the power of implementing data masking directly inside PostgreSQL. Currently it is based on the COMMENT statement (probably the most unused PostgreSQL syntax) and an event trigger. In the near future, I’d like to propose a new syntax for dynamic data masking (MS SQL Server already has it)

The extension can be used to put dynamic masks on certain users or permanently modify sensitive data. Various masking techniques are available : randomization, partial scrambling, custom rules, etc.

Here’s a basic example :

Imagine a people table

=# SELECT * FROM people; id | name | phone ------+----------------+------------ T800 | Schwarzenegger | 0609110911
  1. Activate the masking engine
=# CREATE EXTENSION IF NOT EXISTS anon CASCADE; =# SELECT anon.mask_init();
  1. Declare a masked user
=# CREATE ROLE skynet; =# COMMENT ON ROLE skynet IS 'MASKED';
  1. Declare the masking rules
=# COMMENT ON COLUMN people.name IS 'MASKED WITH FUNCTION anon.random_last_name()'; =# COMMENT ON COLUMN people.phone IS 'MASKED WITH FUNCTION anon.partial(phone,2,$$******$$,2)';
  1. Connect with the masked user
=# \! psql test -U skynet -c 'SELECT * FROM people;' id | name | phone ------+----------+------------ T800 | Nunziata | 06******11

Of course this project is a work in progress. I need yo

[...]
カテゴリー: postgresql

brian davis: A Poor Man's Column Oriented Database in PostgreSQL

planet postgresql - 2018-10-29(月) 10:16:00

Let's get this out of the way. If you need a real column oriented database, use one. Don't even think about using the insanity below in production.

Having said that, I've been wondering for a while if it would be possible to demonstrate the properties of a column oriented db by simulating one using only native functionality found in good old, row oriented, PostgreSQL.

Two properties of a column oriented database that make it beneficial in OLAP environments are

  1. For queries that involve only a subset of a table's columns, it only needs to read the data for those columns off disk, and no others, saving on IO
  2. Storing each column separately means it can compress that data better since it's all of the same type, further reducing IO

The reduction in IO saves time for queries aggregating data over a large fraction of the table, improving performance.

PostgreSQL, of course, is row oriented. It stores and reads data a whole row at a time, and this is great when you want to access a majority of a table's columns for a small percentage of the table. i.e. OLTP type queries.

The challenge will be, can we structure things so PostgreSQL behaves more like a column oriented db?

Strategy

The strategy will be to use multiple tables behind the scenes to store the data for each column individually, and throw a view on top to tie them all together and make it look like a single table. If PostgreSQL's query planner is smart enough, it should be able to see that queries involving only a subset of columns only need to access those particular underlying tables, save on IO, and beat out a traditional PostgreSQL table of the same shape. We can even allow for modifying this pseudo-table by creating INSTEAD OF triggers on the view to take INSERT, UPDATE, DELETE statements, chop them up, and perform the necessary operations on the underlying tables.

Here's how the underlying tables will look. We'll have a single 'primary table' that contains only the primary key...

Table "public.primary_table" Column | Type |[...]
カテゴリー: postgresql

第 154 回理事会議事録 (2018-10)

www.postgresql.jp news - 2018-10-25(木) 19:14:43
第 154 回理事会議事録 (2018-10) anzai 2018/10/25 (木) - 19:14
カテゴリー: postgresql

Tim Colles: string_to_array behaviour with an empty string

planet postgresql - 2018-10-25(木) 17:49:23

So this caught me out the other day. We had a query which broke out multiple delimited strings each with one or more elements (but always the same number of elements in each) into multiple records using string_to_array and unnest. In each string any element could potentially have an empty value, but at least one string would always have values for all the elements. This meant there should always be at least one output row. So below worked as expected:

SELECT UNNEST(STRING_TO_ARRAY(test.s1, '|')) AS col1, UNNEST(STRING_TO_ARRAY(test.s2, '|')) AS col2 FROM ( VALUES (('a|b'),('1|2')) ) AS test(s1, s2);

with the following result:

col1 | col2 ------+------ a | 1 b | 2 (2 rows)

Below worked entirely as expected as well:

SELECT UNNEST(STRING_TO_ARRAY(test.s1, '|')) AS col1, UNNEST(STRING_TO_ARRAY(test.s2, '|')) AS col2 FROM ( VALUES (('a|b'),('|')) ) AS test(s1, s2);

with the following result:

col1 | col2 ------+------ a | b | (2 rows)

So did this when we had some data with just the minimum one element in the input:

SELECT UNNEST(STRING_TO_ARRAY(test.s1, '|')) AS col1, UNNEST(STRING_TO_ARRAY(test.s2, '|')) AS col2 FROM ( VALUES (('a'),('1')) ) AS test(s1, s2);

with the following result:

col1 | col2 ------+------ a | 1 (1 row)

But then we discovered that there was some data that was being completely lost in the query output. Turns out that this occurred when, like above there was just one element in the input, but one value was empty:

SELECT UNNEST(STRING_TO_ARRAY(test.s1, '|')) AS col1, UNNEST(STRING_TO_ARRAY(test.s2, '|')) AS col2 FROM ( VALUES (('a'),('')) ) AS test(s1, s2);

with the following result:

col1 | col2 ------+------ (0 rows)

So after some investigation it turns out that this happens because string_to_array on an empty string returns an array with no elements rather than an array with one element which is an empty string. This does actually make sense because without any application specific context it is indeterminate whether an empty string should be treated a

[...]
カテゴリー: postgresql

Ozgun Erdogan: Why Citus Data is donating 1% equity to PostgreSQL organizations

planet postgresql - 2018-10-24(水) 21:15:00

Today, we’re excited to announce that we have donated 1% of Citus Data’s stock to the non-profit PostgreSQL organizations in the US and Europe. The United States PostgreSQL Association (PgUS) has received this stock grant. PgUS will work with PostgreSQL Europe to support the growth, education, and future innovation of Postgres both in the US and Europe.

To our knowledge, this is the first time a company has donated 1% of its equity to support the mission of an open source foundation.

To coincide with this donation, we’re also joining the Pledge 1% movement, alongside well-known technology organizations such as Atlassian, Twilio, Box, and more.

Why make this donation? Because it’s the right thing to do

At Citus Data, we have a special relationship with PostgreSQL. Our flagship product Citus builds on and transforms Postgres into a distributed database. Our team attends and presents at Postgres conferences. We sponsor PostgreSQL events and meetups. We learn from and contribute back to the community. Our customers use many drivers, tools, and connectors in the Postgres ecosystem.

In short, our team and our company have hugely benefited from Postgres over the years. We owe a lot of our success to the PostgreSQL project and the many talented people involved.

Today, we’re giving back to the community that who made this project so successful.

Why is this important? Because PostgreSQL is the world’s only independent database

PostgreSQL is unique.

Postgres is not only the world’s most advanced open source relational database. It is also the world’s only independent database. No single company backs or represents the Postgres project.

In one sense, the PostgreSQL community came to be, rather than being put together by one company. And the Postgres open source community has been steadily building new features for more than 20 years.

Signage for the first PostgreSQL Conference (PGCon) celebrating 10 years of development, in 2006. Photograph by Oleg Bartunov.

Today, Postgres offers a capable, robust, and popular alternativ

[...]
カテゴリー: postgresql

Nickolay Ihalainen: PostgreSQL locking, part 2: heavyweight locks

planet postgresql - 2018-10-24(水) 20:39:16

PostgreSQL locking visibility for application developers and DBAs is in most cases related to heavyweight locks. Complex database locking operations require full instrumentation using views from the system catalog. It should be clear which object is locked by a specific database “backend” process. An alternative name for any lock is “bottleneck”. In order to make database operations parallel we should split a single bottleneck into multiple operation specific tasks.

This is the second part of three blog posts related to table level locks. The previous post was about row-level locks, and a subsequent post reviews the latches protecting internal database structures.

Example environment

A simple table with several rows:

CREATE TABLE locktest (c INT); INSERT INTO locktest VALUES (1), (2); Helper view

In order to check different types of these locks, let’s create a helper view as suggested by Bruce Momjian in his presentation:

CREATE VIEW lockview AS SELECT pid, virtualtransaction AS vxid, locktype AS lock_type, mode AS lock_mode, granted, CASE WHEN virtualxid IS NOT NULL AND transactionid IS NOT NULL THEN virtualxid || ' ' || transactionid WHEN virtualxid::text IS NOT NULL THEN virtualxid ELSE transactionid::text END AS xid_lock, relname, page, tuple, classid, objid, objsubid FROM pg_locks LEFT OUTER JOIN pg_class ON (pg_locks.relation = pg_class.oid) WHERE -- do not show our view’s locks pid != pg_backend_pid() AND -- no need to show self-vxid locks virtualtransaction IS DISTINCT FROM virtualxid -- granted is ordered earlier ORDER BY 1, 2, 5 DESC, 6, 3, 4, 7; RowShareLock (ROW SHARE)

Many applications use the read-modify-write paradigm. For instance, the appl

[...]
カテゴリー: postgresql

David Rowley: PostgreSQL 11: Partitioning Evolution from Postgres 9.6 to 11

planet postgresql - 2018-10-24(水) 18:17:41

During the PostgreSQL 11 development cycle an impressive amount of work was done to improve table partitioning.  Table partitioning is a feature that has existed in PostgreSQL for quite a long time, but it really wasn’t until version 10 that it started to become a highly useful feature. We’d previously claimed that table inheritance was our implementation of partitioning, which was true.  It just left you to do much of the work yourself manually. For example, during INSERTs, if you wanted the tuples to make it to your partitions then you had to set up triggers to do that for you. Inheritance partitioning was also slow and hard to develop additional features on top of.

In PostgreSQL 10 we saw the birth of “Declarative Partitioning”, a feature which is designed to solve many of the problems which were unsolvable with the old inheritance method of partitioning. This has resulted in a much more powerful tool to allow you to horizontally divide up your data!

Feature Comparison

PostgreSQL 11 comes complete with a very impressive set of new features to both help improve performance and also to help make partitioned tables more transparent to applications.

Feature PG9.6 PG10 PG11 Declarative Partitioning Auto Tuple Routing – INSERT Auto Tuple Routing – UPDATE Optimizer Partition Elimination  1 1 Executor Partition Elimination 2 Foreign keys 3 Unique indexes 4 Default Partitions Hash Partitions FOR EACH ROW triggers Partition-level joins  5 Partition-level aggregation Foreign partitions Parallel Partition Scans
  1. Using constraint exclusion
  2. Append nodes only
  3. On partitioned table referencing non-partitioned table only
  4. Indexes must contain all partition key columns
  5. Partition constraint on both sides must match exactly

 

Performance

We’ve also got good news here!  A new method of performing partition elimination has been added. This new algorithm is able to determine matching partitions by looking at the query’s WHERE clause. The previous algo

[...]
カテゴリー: postgresql

Quinn Weaver: How to set up scram-sha-256 authentication in PostgreSQL

planet postgresql - 2018-10-24(水) 15:09:00
md5: everyone uses it. But it's insecure — unsuitable for authentication or password storage. PostgreSQL 10 adds support for SCRAM SHA-256 authentication, which is far better1… but how do you use it? Documentation is scarce.

Below I give the complete steps, for two different cases:
  • The case where you migrate every user.
  • The case where you migrate only a subset of users. Step 1 explains why you might need to do this. In this case, you can save time and complexity by creating a containing role, adding all the users you want to migrate to that role, and then configuring that role to work with scram-sha-256. That way you don't have to do it once for each user.
Enough preamble; let's begin!
  1. First, decide which users to migrate to scram-sha-256. The ideal is to migrate everyone, all at once. In practice you may be unable to do that, for a few reasons:
    • Older client tools don't support scram-sha-256. You need at least psql 10, or pgAdmin 4.
    • Your app's client libraries may not support scram-sha-256. At a minimum, you will probably have to upgrade your client libraries2.
    • And it's not enough just to upgrade your libraries; you also have to change the password for each user who's migrating, because PostgreSQL needs to hash this password in scram-sha-256 format. There's no automatic rehash (there can't be, since PostgreSQL doesn't store the cleartext of the old password).
    • Finally, besides your own code, you may have third-party apps connecting to your database, whose library versioning policy and password reset policy you don't control.
  2. Having chosen the users to migrate, upgrade your relevant client libraries, psql/postgresql-client packages, and/or pgAdmin versions.
  3. If you're migrating all users, skip to the next step. If, instead, you're migrating a subset of users, then create a new role, and put all those users in that role. This step saves a bit of repetitive config work. $ sudo su - postgres
    psql
    postgres=# create role scram_sha_256_users nologin ROLE alice, bob, eve; … where alice, bob, and eve are the users yo
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カテゴリー: postgresql

Joshua Drake: PostgresConf Silicon Valley recap

planet postgresql - 2018-10-24(水) 03:31:00


PostgresConf ran its first Silicon Valley conference on October 15th and 16th in conjunction with Silicon Valley Postgres. The two day conference was considered a “local” or development conference where our focus was introducing the PostgresConf experience to new attendees and partners with world class content. We believe we succeeded in that.

We brought new friends to the community with the addition of Yugabyte, Scalegrid, and AgensGraph. We also had old friends return with Pivotal, AWS, Microsoft, 2ndQuadrant, Timescale, Compose, and Nutanix.

This is the first conference we have organized where the attendance went up during the conference. All community conferences know the stress of waiting for people to register. We all register at the last possible moment but for attendance to increase as the conference is running was new for us. It added a new level of legitimacy to our purpose of:

The conference had 139 attendees and as the goal was 100-150, we are quite pleased with the turn out. We will be returning in 2019 and we look forward to continuing to build the Silicon Valley Community.
Thank you to the attendees, supporters, and organizers for helping pull off yet another amazing event!
カテゴリー: postgresql

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