0
votes
0answers
34 views

postgres explain plan with giant gaps between operations

I have a postgresql explain plan that seems to have large gaps between the join, sort & filter processes and can't explain (sorry) it. The query is taking an inordinate amount of time and the ...
2
votes
1answer
109 views

Optimal hash technique to index large text

Erwin Brandstetter thankfully saved me from myself when I tried to create unique indexes on textual columns with large lengths. The upper limit for the insertion rate is tens of billions of rows per ...
2
votes
0answers
39 views

Efficiently joining two irregular series representing changes

(This is a PostgreSQL-specific question, using version 9.1, but could be upgraded to 9.3.) I have a number of tables that represent a series of changes. These tables all have the same structure: ...
1
vote
1answer
46 views

Postgres: my “data/backup” directory is way too large

In my postgres 9.3 data directory, there exists a subdir called "backup" that is 6.1G compared to my pg_xlog which is only 130M. I understand that pg_xlog is the WAL logs, so what is in the backup? ...
5
votes
0answers
89 views

Modification to GEQO (Genetic Query Optimization) of PostgreSQL

I need to implement a functionality that is in line with the GEQO functionality of PostgreSQL. I understand that GEQO approach is to encode query plans as integer strings and GEQO generates these ...
1
vote
1answer
245 views

How can I speed up a Postgres query containing lots of Joins with an ILIKE condition

I have an odd problem which I really don't understand. Simply put I have a join containing 4 table joins, which I believe all have appropriate indexes, but which takes a ridiculous amount of time to ...
0
votes
1answer
62 views

How to index WHERE (start_date >= '2013-12-15')

I have a table named items, and inside the table there is a some_date column, with date as the datatype. I was wondering how can I index the some_date column with PostgreSQL SELECT "items".* FROM ...
0
votes
0answers
38 views

Optimizing PostgreSQL 9.0.2

For work we have a 8GB Linode, hosting both the Rails 3 App (Passenger, Apache) and Postgres. The app is a reading heavy app, about 75% reading, and 25% writing. (A conservative estimate would be ...
2
votes
1answer
97 views

Has postgresql a fast add column optimization?

When adding not-null columns with a default value - does Postgresql optimizes this operation? In case the table has n rows, a not-optimized alter-table-add-column would yield n writes of the default ...
10
votes
3answers
446 views

Indexes for SQL query with WHERE condition and GROUP BY

I am trying to determine which indexes to use for an SQL query with a WHERE condition and a GROUP BY which is currently running very slow. My query: SELECT group_id FROM counter WHERE ts between ...
1
vote
2answers
113 views

optimization of expensive subquery

The following query gets the last report (where latitude and longitude and secs are <> 0) associated with the specified units: SELECT reports.* FROM reports INNER JOIN ...
2
votes
1answer
36 views

General purpose view for last value in a group

I am trying to create a view to show the last value in the group. Looking for a more general purpose query. CREATE TABLE a ( id INTEGER, seq INTEGER, val VARCHAR2(16), PRIMARY ...
0
votes
1answer
256 views

PostgreSQL FTS and Trigram-similarity Query Optimization

I have recently started working on PostgreSQL and I have around 12M rows to handle in which I want to apply Full Text Search. I don't have any prior experience in handling such databases. I have tried ...
0
votes
1answer
74 views

Complex “activity” based query optimization

I'm working on a query in the same style as Facebook's feed on a table that currently has 500,000 rows. For now I am just looking to get the 20 newest items (new records created by a user's ...
8
votes
1answer
216 views

Why are the plans different if the queries are logically alike?

I wrote two functions to answer Day 3's first homework question from Seven Databases in Seven Weeks. Create a stored procedure where you can input a movie title or actor's name you like, and it ...
5
votes
1answer
485 views

Schema for analytics table in Postgres

We use Postgres for analytics (star schema). Every few seconds we get reports on ~500 metrics types. The simplest schema would be: timestamp metric_type value 78930890 FOO ...
2
votes
0answers
343 views

Query optimization on a large table in PostgreSQL

I am not super experienced with databases, just have a college level course under my belt. I am trying to see if an existing query can be optimized. Currently on average takes over 300ms. There is a ...
3
votes
1answer
98 views

PL/pgSQL functions and optimizations fences?

I am newbie on DB stuff. And my DB knowledge is very old (around MSSQL2000). All what I remember is, the stored procedures are faster than ordinary queries because it avoid query compilation and ...
1
vote
0answers
114 views

Postgres - Partitioning old tables, partition query planning, optimisation

I've been trying to optimise our database, but not being a DBA and not having done a whole lot of tuning before I'm struggling a little with "too many options". I've already run pg_tune and bumped a ...
6
votes
1answer
299 views

Optimizing PostgreSQL for transient data

I have several tables with 100-300 columns of integer types each, that hold highly volatile data. The datasets are keyed by one or two primary keys, and when refresh occurs, the whole dataset is ...
1
vote
2answers
164 views

Prune unused joins

I have expected that selecting from a view would not join the tables from which I don't query any values, but it doesn't seem to be the case. I have a bunch of tables with the following structure: ...
3
votes
1answer
135 views

How un-clustered is a CLUSTER USING table in PostgreSQL

I have some tables which benefit greatly from CLUSTER ON/CLUSTER USING in Postgres SQL: # CLUSTER table USING index_name; # ANALYZE VERBOSE table; # CLUSTER VERBOSE; A maintenance task periodically ...
4
votes
1answer
543 views

Postgres: count(*) vs count(id)

I saw in the documentation the difference between count(*) and count(pk). I had been using count(pk) (where pk is a SERIAL PRIMARY KEY) not knowing about the existence of count(*). My question is ...
7
votes
3answers
6k views

Optimizing queries on a range of timestamps (two columns)

I use postgresql-9.1 with ubuntu 12.04. I need to select records inside a range of time: my table time_limits has two timestamp fields and one property integer. Indeed there are other info columns ...
1
vote
1answer
874 views

Correct use of VOLATILE COST (and ROWS) indications in Postgresql stored procedure

While looking at several examples of pl/python and pl/pgsql, I have seen many - but not all - using volatile cost. ie: CREATE OR REPLACE FUNCTION my_function() RETURNS setof record AS $BODY$ -- ...
0
votes
1answer
63 views

Faster joining on 'most recent' related rows

I have a bug tracking application. The bug table stores very little, because every state change to a bug happens by adding a comment. For example, the current state of a bug is determined by the state ...
1
vote
1answer
107 views

Does PostgreSQL optimize queries in transaction?

In my app I need to make big imports from user files, and to achieve that all records are updated/created I do it inside transaction. But before it I need to update massive, already existing in DB, ...
4
votes
1answer
222 views

Does the order of fields in SELECT query matter when using composite indexing?

I understand that the order of columns in the index itself matters immensely; however, what about the order of columns in the subsequent SELECT queries that make use of that index? For example, if I ...
2
votes
0answers
363 views

Best book on query optimization, rewriting, refactoring [closed]

I have a specific problem: huge amounts of Web-related data in Postgres db. The queries running against the data are often very inefficient. But in a more general sense, I need a book that explains ...
5
votes
1answer
181 views

Determining which isolation level is appropriate

This is a homework question. For the following transactions state the isolation level that will maximize throughput without lowering the integrity of the database. Explain the answer. ...
1
vote
0answers
313 views

Finding the bottleneck by analyzing Munin graphs

We’ve been experiencing some issues with our database server during peak hours. In our Nginx error-log we can see that a lot of requests get timed out. The requests are also very slow. We have had ...
1
vote
1answer
353 views

PostgreSQL 9.1 - Asynchroneous commits performance boost

During peak hours our users experience a lot of timeouts due to an overloaded database server. We are currently trying to make optimizations in order to cope with the high traffic. We read in the ...
7
votes
1answer
448 views

Is the optimisation fence behaviour of a CTE (WITH query) specified in the SQL:2008 standard? If so, where?

I see frequent references to WITH queries (common table expressions, or CTEs) acting as an optimisation fence, where the server isn't permitted to push filters down into the CTE queries, pull common ...
1
vote
1answer
90 views

Optimising query on view that merges similar tables with a clear discriminator

Using PostgreSQL 8.4, I have a number of tables that have a very similar structure, but that belong to different categories: CREATE TABLE table_a ( id SERIAL PRIMARY KEY, event_time TIMESTAMP ...
2
votes
1answer
2k views

PostgreSQL tree structure and recursive CTE optimization

I'm trying to represent a tree structure in PostgreSQL (8.4) to be able to query the path from the root to a given node or to find all the nodes within a sub-branch. Here is a test table: CREATE ...
4
votes
2answers
403 views

Huge database logging of event type rows and ways to optimize it

We have a database that stores events. Events are generated at a 1000 per sec rate. We need to keep these events accessible for some years. Usual use of these events is selecting some of them from the ...
2
votes
2answers
1k views

Fastest validation query in PostgreSQL

What is the fastest query in PostgreSQL, which I can use as a validationQuery binding a JNDI resource? I though that SELECT 1 is the simplest, but in this document it is said that in PostgreSQL we ...
1
vote
3answers
224 views

PostgreSQL and query planner

I have question about query planner in PostgreSQL. I know, that this planner is taking data from pg_statistics, but... Can anyone tell me on what basis this planner is taking those informations to ...