2
votes
2answers
83 views

Is it always faster to create indexes after loading data?

I have a large number of records (~1 billion) that I need to load into MongoDB (actually TokuMX, but whatever). I have about 6 different indices I need to create on the collection. Is it always faster ...
2
votes
1answer
120 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
1answer
114 views

Is there a negative effect if I place an index on every column in a wide table?

We have a wide dataset that isn't very tall (say 250K rows, 90 columns). We will be providing users with an interface that allows them to generate arbitrary queries against this dataset. They can ...
2
votes
1answer
129 views

How to get rid of clustered index scan?

I have a query that was generated by C#/Linq-To-Entities code. As with this kind of query, it looks seriously ugly and I doubt it would help to include it here. But I have run it through a query ...
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 ...
10
votes
3answers
496 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
62 views

index for OR operator with different columns

What would be best index for this kind of query: -- id is the PK create table test3(id number,name varchar2(30) not null,lastname varchar2(30) not null); select id from test3 where id=:1 and ...
0
votes
1answer
57 views

Optimize query to minimize tmp copying time

I have this mega query : SELECT s.eleve_id, crs.id_cours as 'cours_id', mc.code as cours_code, s.employe_id, s.id_seance, '0' as theorique, s.statut, s.type_vehicule_id, s.type_conduite_id, ...
0
votes
1answer
278 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
0answers
53 views

is it good to add index on column used in group by clause?

I have a query like- select x, sum(y) from xyz where z>=100 group by x order by sum(y) desc; will it be faster if I am going to add index on x?
1
vote
1answer
76 views

How is the number of records on a select determined as high or low by optimizer?

What is the threshold between using the index and doing an direct access to the database? I assume this decision is related to the number of index access (and subsequent access to the tables). If this ...
0
votes
1answer
98 views

SQL Server Index Scan Actual Executions

I have a fairly complicated query and running it on two databases with same schemas, but with different data produces different result. On database D1 the elapsed time is around 1 second, and the ...
2
votes
2answers
116 views

Optimize query or model, to get an population overview in time

I think I've got a very simple model and query, but I cannot find a way to make use of indexes to boost performance. I wonder if there is a trick in my model, or MySQL query, to speed up the ...
5
votes
3answers
4k views

Why does MySQL ignore the index even on force for this order by?

I run an EXPLAIN: mysql> explain select last_name from employees order by last_name; +----+-------------+-----------+------+---------------+------+---------+------+-------+----------------+ | ...
0
votes
2answers
274 views

How to index for a query with independent range conditions?

What is the best way to index a table that I query using independent range conditions? E.g. WHERE X < ? and Y > ?
3
votes
1answer
376 views

mysql: need help to optimize my query/table

I'm wondering if someone could help me optimize my tables/query to speed up a query. It is currently running ridiculously slow. I think a well-thought out index could help me. Any help would be really ...
8
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 ...
4
votes
1answer
1k views

Indexing strategy when using the between operator SQL Server 2008

I have a large table ~25 million rows with the structure CREATE TABLE [dbo].[rx]( [pat_id] [int] NOT NULL, [fill_Date] [date] NOT NULL, [script_End_Date] AS ...
4
votes
1answer
234 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 ...
3
votes
1answer
207 views

Query optimization with extreme statistic

I have a table: mysql> describe table_1; +---------------+------------------+------+-----+---------------------+----------------+ | Field | Type | Null | Key | Default ...
2
votes
2answers
108 views

Optimizing index creation

One thing that has bothered me for awhile is creating many many indexes for the one table where the query only differs slightly or contains many of the same columns. An example case would be: table1 ...
2
votes
2answers
2k views

How do I force a JOIN to use a specific index in MySQL?

I have a query that JOINs 2 tables; lineitem and part, select sum(l_extendedprice* (1 - l_discount)) as revenue from lineitem force index for join (l_pk), part where ( ...
5
votes
1answer
209 views

Walking a BTREE index as far as possible in MySQL

Suppose one has a column of words on which one builds a BTREE index: CREATE TABLE myTable ( words VARCHAR(25), INDEX USING BTREE (words) ); LOAD DATA LOCAL INFILE '/usr/share/dict/words' INTO ...
2
votes
1answer
2k views

MySQL Explain: Using index, using temporary, using filesort. Can this query be improved?

I'm working on a event tracking system which uses a handful of lookup tables as well as the primary logging table. In a report I'm writing, an object can be selected to view statistics against. The ...
2
votes
1answer
737 views

Is a query with UNIX_TIMESTAMP using indexes in mysql?

If I use .. WHERE UNIX_TIMESTAMP(`some_timestamp`)>NOW() in a SELECT, does this query still make use on an index, set on some_timestamp ?
5
votes
3answers
406 views

Database Indexing - Maintenance Jobs

I have created a script that runs every night to rebuild & re-organize indexes based on the fragmentation, Indexes with Fragmentation > 30% are rebuilt, Indexes with Fragmentation 10% - 30% are ...
1
vote
1answer
586 views

Slow insert with MySQL full-text index

I use a full-text index in a MySQL table, and each insert into this table takes about 3 seconds. It seems that MySQL rebuilds (a part) of the full text index after each insert/update. Is this right? ...
7
votes
2answers
4k views

Why is this query not using my nonclustered index, and how can I make it?

As follow up to this question about increasing query performance, I'd like to know if there is a way to make my index used by default. This query runs in about 2.5 seconds: SELECT TOP 1000 * FROM ...
2
votes
2answers
123 views

Why isn't the following query using the `always` index?

This morning I started receiving load warnings on one of the MySQL servers I manage. SHOW FULL PROCESSLIST revealed that the culprit was the following (poorly written) query: SELECT * FROM movies, ...
1
vote
1answer
1k views

At which frequency run CTXSYS.CTX_DDL.OPTIMIZE_INDEX(…) on a fulltext index?

I've been told to run periodically CTXSYS.CTX_DDL.OPTIMIZE_INDEX(...) on some fulltext indexes, with no more information, in particular at which frequency this task should be run. I guess that it ...
2
votes
2answers
199 views

In MySQL, should I add an index even if the query that scans the table is only ran once a month?

Concretely, is it worth it to add an index to a query that scans the table of a mysql database, even if that index would only be used once a month? For example, having a users a table and then ...
1
vote
1answer
247 views

Optimising a sql correlated subquery statement

I am updating a column on tableA with data from tableB like this: update tableA set bKey = select bKey from tableB B where B.colB = tableA.colB bKey has a unique index on tableB. Which is the ...
8
votes
4answers
1k views

How can I optimize this MySQL query further?

I have a query that is taking a particularly long time to run (15+ seconds) and it is only getting worse with time as my dataset grows. I have optimized this in the past, and have added indices, ...
9
votes
5answers
2k views

How do I query this 20 million record view faster?

For a search functionality I am using a view that has the records from all the tables within which I need to search for. The view has almost 20 million records. Searches against this view are taking ...
5
votes
4answers
4k views

MySQL: Index when joining to tables not being used (Performance optimizing question)

I need to optimize the following query: SELECT /* [things omitted] */ articles.blogpost_id, articles.id AS articleid FROM blogposts JOIN articles ON articles.blogpost_id = blogposts.id WHERE ...
4
votes
2answers
162 views

How to create multiple entries on index based on the fields of one row?

I never found a good way to index multiple fields of one row as entries of an index or simulate this feature on MySQL. The problem arises when you have fields working as tags or similar concept. Ex.: ...
54
votes
6answers
19k views

How to determine if an Index is required or necessary

I've been running an auto-index tool on our MS SQL database (I modified a script originating from Microsoft that looks at the index statistics tables - Automated Auto Indexing). From the stats, I now ...