Consider this SQL statement:
select *
from chamado.servico se
join chamado.chamado ch on ch.id_servico=se.id_servico
join chamado.statuschamado sc on sc.id_statuschamado=ch.id_statuschamado
where sc.id_statuschamado=1
;
Now consider the corresponding execution plan:
Now Pay close attention ibn the red box! The filter predicate (CH.ID_STATUSCHAMADO=1). It is not in the query and it is the most expensive operation.
The table SERVICO has less than 200 rows, the table STATUSCHAMADO has less than 10 rows, but the table CHAMADO has more than 70000 rows.
My intention with those joins where to have full table scan only on STATUSCHAMADO and SERVICO, what was supposed to impose a lite overhead on Oracle.
What is wrong in my statement?
Update 1
I have the following indices:
CHAMADO.ID_CHAMADO (PK)
CHAMADO.ID_SERVICO
CHAMADO.ID_AREAATENDIMENTO
SERVICO.ID_SERVICO (PK)
AREAATENDIMENTO.ID_AREAATENDIMENTO (PK)
"The filter predicate (CH.ID_STATUSCHAMADO=1)...is not in the query" - perhaps not directly, but that's what's really happening. You're joining STATUSCHAMADO sc to CHAMADO ch on sc.ID_STATUSCHAMADO = ch.ID_STATUSCHAMADO, then in your WHERE clause you have sc.ID_STATUSCHAMADO = 1.
The database is smart enough to figure out that sc.ID_STATUSCHAMADO will always be 1, and therefore can substitute CHAMADO.ID_STATUSCHAMADO = 1. You also might try reversing the fields on the new index on STATUSCHAMADO - try it as (ID_STATUSCHAMADO, ID_SERVICO) as well as (ID_SERVICO, ID_STATUSCHAMADO).
Related
In my power Bi I would like to count rows for all my tables and having this output:
Table Name
Row count
Table1
126
Table2
985
Table3
998
...
...
As long as I have few tables I can do
NEWTABLE = UNION(
ROW("TableName","Table1", "Rowcount",ROWSCOUNT(Table1)),
ROW("TableName","Table2", "Rowcount",ROWSCOUNT(Table2)),
...
)
But this starts to be complicated when I have many tables.
Is there a way I can do it? Like a loop or something?
Thank you
If you only need a metrics then you can use DaxStudio -> ViewMetrics
where cardinality is your "rowCounts"
If you need something more, then you can get all table name from DMV
select * from $SYSTEM.TMSCHEMA_TABLES
populate this as another table in your model, and use M language to loop through.
here useful example:
https://community.powerbi.com/t5/Power-Query/Power-query-Counting-rows-from-all-table-in-query-editor-but-not/td-p/1198489
I'm trying to speed up the following
create table tab2 parallel 24 nologging compress for query high as
select /*+ parallel(24) index(a ix_1) index(b ix_2)*/
a.usr
,a.dtnum
,a.company
,count(distinct b.usr) as num
,count(distinct case when b.checked_1 = 1 then b.usr end) as num_che_1
,count(distinct case when b.checked_2 = 1 then b.usr end) as num_che_2
from tab a
join tab b on a.company = b.company
and b.dtnum between a.dtnum-1 and a.dtnum-0.0000000001
group by a.usr, a.dtnum, a.company;
by using indexes
create index ix_1 on tab(usr, dtnum, company);
create index ix_2 on tab(usr, company, dtnum, checked_1, checked_2);
but the execution plan tells me that it's going to be an index full scan for both indexes, and the calculations are very long (1 day is not enough).
About the data. Table tab has over 3 mln records. None of the single columns are unique. The unique values here are pairs of (usr, dtnum), where dtnum is a date with time written as a number in the format yyyy,mmddhh24miss. Columns checked_1, checked_2 have values from set (null, 0, 1, 2). Company holds an id for a company.
Each pair can only have one value checked_1, checked_2 and company as it is unique. Each user can be in multple pairs with different dtnum.
Edit
#Roberto Hernandez: I've attached the picture with the execution plan. As for parallel 24, in our company we are told to create tables with options 'parallel [num] nologging compress for query high'. I'm using 24 but I'm no expert in this field.
#Sayan Malakshinov: http://sqlfiddle.com/#!4/40b6b/2 Here I've simplified by giving data with checked_1 = checked_2, but in real life this may not be true.
#scaisEdge:
For
create index my_id1 on tab (company, dtnum);
create index my_id2 on tab (company, dtnum, usr);
I get
For table tab Your join condition is based on columns
company, datun
so you index should be primarly based on these columns
create index my_id1 on tab (company, datum);
The indexes you are using are useless because don't contain in left most position columsn use ij join /where condition
Eventually you can add user right most potition for avoid the needs of table access and let the db engine retrive alla the inf inside the index values
create index my_id1 on tab (company, datum, user, checked_1, checked_2);
Indexes (bitmap or otherwise) are not that useful for this execution. If you look at the execution plan, the optimizer thinks the group-by is going to reduce the output to 1 row. This results in serialization (PX SELECTOR) So I would question the quality of your statistics. What you may need is to create a column group on the three group-by columns, to improve the cardinality estimate of the group by.
My Query is
SELECT unnest(array [repgroupname,repgroupname||'-'
||masteritemname,repgroupname||'-' ||masteritemname||'-'||itemname]) AS grp
,unnest(array [repgroupname,masteritemname,itemname]) AS disp
,groupname1
,groupname2
,groupname3
,sum(qty) AS qty
,sum(freeqty) AS freeqty
,sum(altqty) AS altqty
,sum(discount) AS discount
,sum(amount) AS amount
,sum(stockvalue) AS stockvalue
,sum(itemprofit) AS itemprofit
FROM (
SELECT repgroupname
,masteritemname
,itemname
,groupname1
,groupname2
,groupname3
,units
,unit1
,unit2
,altunits
,altunit1
,altunit2
,sum(s2.totalqty) AS qty
,sum(s2.totalfreeqty) AS freeqty
,sum(s2.totalaltqty) AS altqty
,sum(s2.totaltradis + s2.totaladnldis) AS discount
,sum(amount) AS amount
,sum(itemstockvalue) AS stockvalue
,sum(itemprofit1) AS itemprofit
FROM sales1 s1
INNER JOIN sales2 s2 ON s1.txno = s2.txno
INNER JOIN items i ON i.itemno = s2.itemno
GROUP BY repgroupname
,masteritemname
,itemname
,groupname1
,groupname2
,groupname3
,units
,unit1
,unit2
,altunits
,altunit1
,altunit2
ORDER BY itemname
) AS tt
GROUP BY grp
,disp
,groupname1
,groupname2
,groupname3
Here
Sales1 table have 144513 Records
Sales2 Table have 438915 Records
items Table have 78512 Records
This Query take 6 seconds to produce result.
How to Optimize this query?
am using postgresql 9.3
That is a truly horrible query.
You should start by losing the ORDER BY in the sub-select - the ordering is discarded by the outer query.
Beyond that, ask yourself why you need to look to see a summary of every songle row in th DBMS - does this serve any useful purpose (if the query is returning more than 20 rows, then the answer is no).
You might be able to make it go faster by ensuring that the foreign keys in the tables are indexed (indexes are THE most important bit of information to look at whenever you're talking about performance and you've told us nothing about them).
Maintaining the query as a regular snapshot will mitigate the performance impact.
I've got this two index:
CREATE INDEX NETATEMP.CAMBI_MEM_ANIMALI_ELF_T2A ON NETATEMP.CAMBI_MEM_ANIMALI_ELF_T2
(TELE_TESTATA_LETTURA_ID, ELF_DATA_FINE_FATTURAZIONE)
CREATE INDEX NETATEMP.LET_TESTATE_LETTURE1A ON NETATEMP.LET_TESTATE_LETTURE1
(TELE_STORICO_ID, TRUNC("TELE_DATA_LETTURA"))
CREATE TABLE NETATEMP.cambi_mem_animali_elf
AS
SELECT --/*+ parallel(forn 32) */
DISTINCT
forn_fornitura_id,
TRUNC (tele.TELE_DATA_LETTURA) TELE_DATA_LETTURA,
forn.edw_partition,
DECODE (SUBSTR (forn.TELE_TESTATA_LETTURA_ID, 1, 1), '*', 'MIGRATO', 'INTEGRA') Origine
FROM NETATEMP.cambi_mem_animali_elf_t2 forn,
netatemp.let_testate_letture1 tele
WHERE forn.tele_testata_lettura_id = tele.tele_storico_id
--
AND forn.ELF_DATA_FINE_FATTURAZIONE != TRUNC (tele.TELE_DATA_LETTURA)
It uses two full table scan. I simply can't understand why Oracle doesn't look at both index and makes and index range scan after that.
How can I force to do so?
It's because HASH joins don't use indexes on the join predicates.
Read this for all the details: http://use-the-index-luke.com/sql/join/hash-join-partial-objects
You are referencing columns that are not included in the indexes, so even if the join itself would be faster using index, Oracle would anyway have to retrieve all the table blocks for the remaining columns.
For reference: Depending on statistics you may get the index join you are looking for with the first of these two queries because it can be resolved with index only, whereas the second query has to go to the table.
select count(*)
from netatemp.cambi_mem_animali_elf_t2 forn
,netatemp.let_testate_letture1 tele
where forn.tele_testata_lettura_id = tele.tele_storico_id;
select count(*), min(forn.edw_partition)
from netatemp.cambi_mem_animali_elf_t2 forn
,netatemp.let_testate_letture1 tele
where forn.tele_testata_lettura_id = tele.tele_storico_id;
If you have the partitioning option then consider hash partitioning the two tables on the join columns. A partition-wise join will greatly reduce the memory requirement and likelihood of the join spilling to disk.
Have the following tables (Oracle 10g):
catalog (
id NUMBER PRIMARY KEY,
name VARCHAR2(255),
owner NUMBER,
root NUMBER REFERENCES catalog(id)
...
)
university (
id NUMBER PRIMARY KEY,
...
)
securitygroup (
id NUMBER PRIMARY KEY
...
)
catalog_securitygroup (
catalog REFERENCES catalog(id),
securitygroup REFERENCES securitygroup(id)
)
catalog_university (
catalog REFERENCES catalog(id),
university REFERENCES university(id)
)
Catalog: 500 000 rows, catalog_university: 500 000, catalog_securitygroup: 1 500 000.
I need to select any 50 rows from catalog with specified root ordered by name for current university and current securitygroup. There is a query:
SELECT ccc.* FROM (
SELECT cc.*, ROWNUM AS n FROM (
SELECT c.id, c.name, c.owner
FROM catalog c, catalog_securitygroup cs, catalog_university cu
WHERE c.root = 100
AND cs.catalog = c.id
AND cs.securitygroup = 200
AND cu.catalog = c.id
AND cu.university = 300
ORDER BY name
) cc
) ccc WHERE ccc.n > 0 AND ccc.n <= 50;
Where 100 - some catalog, 200 - some securitygroup, 300 - some university. This query return 50 rows from ~ 170 000 in 3 minutes.
But next query return this rows in 2 sec:
SELECT ccc.* FROM (
SELECT cc.*, ROWNUM AS n FROM (
SELECT c.id, c.name, c.owner
FROM catalog c
WHERE c.root = 100
ORDER BY name
) cc
) ccc WHERE ccc.n > 0 AND ccc.n <= 50;
I build next indexes: (catalog.id, catalog.name, catalog.owner), (catalog_securitygroup.catalog, catalog_securitygroup.index), (catalog_university.catalog, catalog_university.university).
Plan for first query (using PLSQL Developer):
http://habreffect.ru/66c/f25faa5f8/plan2.jpg
Plan for second query:
http://habreffect.ru/f91/86e780cc7/plan1.jpg
What are the ways to optimize the query I have?
The indexes that can be useful and should be considered deal with
WHERE c.root = 100
AND cs.catalog = c.id
AND cs.securitygroup = 200
AND cu.catalog = c.id
AND cu.university = 300
So the following fields can be interesting for indexes
c: id, root
cs: catalog, securitygroup
cu: catalog, university
So, try creating
(catalog_securitygroup.catalog, catalog_securitygroup.securitygroup)
and
(catalog_university.catalog, catalog_university.university)
EDIT:
I missed the ORDER BY - these fields should also be considered, so
(catalog.name, catalog.id)
might be beneficial (or some other composite index that could be used for sorting and the conditions - possibly (catalog.root, catalog.name, catalog.id))
EDIT2
Although another question is accepted I'll provide some more food for thought.
I have created some test data and run some benchmarks.
The test cases are minimal in terms of record width (in catalog_securitygroup and catalog_university the primary keys are (catalog, securitygroup) and (catalog, university)). Here is the number of records per table:
test=# SELECT (SELECT COUNT(*) FROM catalog), (SELECT COUNT(*) FROM catalog_securitygroup), (SELECT COUNT(*) FROM catalog_university);
?column? | ?column? | ?column?
----------+----------+----------
500000 | 1497501 | 500000
(1 row)
Database is postgres 8.4, default ubuntu install, hardware i5, 4GRAM
First I rewrote the query to
SELECT c.id, c.name, c.owner
FROM catalog c, catalog_securitygroup cs, catalog_university cu
WHERE c.root < 50
AND cs.catalog = c.id
AND cu.catalog = c.id
AND cs.securitygroup < 200
AND cu.university < 200
ORDER BY c.name
LIMIT 50 OFFSET 100
note: the conditions are turned into less then to maintain comparable number of intermediate rows (the above query would return 198,801 rows without the LIMIT clause)
If run as above, without any extra indexes (save for PKs and foreign keys) it runs in 556 ms on a cold database (this is actually indication that I oversimplified the sample data somehow - I would be happier if I had 2-4s here without resorting to less then operators)
This bring me to my point - any straight query that only joins and filters (certain number of tables) and returns only a certain number of the records should run under 1s on any decent database without need to use cursors or to denormalize data (one of these days I'll have to write a post on that).
Furthermore, if a query is returning only 50 rows and does simple equality joins and restrictive equality conditions it should run even much faster.
Now let's see if I add some indexes, the biggest potential in queries like this is usually the sort order, so let me try that:
CREATE INDEX test1 ON catalog (name, id);
This makes execution time on the query - 22ms on a cold database.
And that's the point - if you are trying to get only a page of data, you should only get a page of data and execution times of queries such as this on normalized data with proper indexes should take less then 100ms on decent hardware.
I hope I didn't oversimplify the case to the point of no comparison (as I stated before some simplification is present as I don't know the cardinality of relationships between catalog and the many-to-many tables).
So, the conclusion is
if I were you I would not stop tweaking indexes (and the SQL) until I get the performance of the query to go below 200ms as rule of the thumb.
only if I would find an objective explanation why it can't go below such value I would resort to denormalisation and/or cursors, etc...
First I assume that your University and SecurityGroup tables are rather small. You posted the size of the large tables but it's really the other sizes that are part of the problem
Your problem is from the fact that you can't join the smallest tables first. Your join order should be from small to large. But because your mapping tables don't include a securitygroup-to-university table, you can't join the smallest ones first. So you wind up starting with one or the other, to a big table, to another big table and then with that large intermediate result you have to go to a small table.
If you always have current_univ and current_secgrp and root as inputs you want to use them to filter as soon as possible. The only way to do that is to change your schema some. In fact, you can leave the existing tables in place if you have to but you'll be adding to the space with this suggestion.
You've normalized the data very well. That's great for speed of update... not so great for querying. We denormalize to speed querying (that's the whole reason for datawarehouses (ok that and history)). Build a single mapping table with the following columns.
Univ_id, SecGrp_ID, Root, catalog_id. Make it an index organized table of the first 3 columns as pk.
Now when you query that index with all three PK values, you'll finish that index scan with a complete list of allowable catalog Id, now it's just a single join to the cat table to get the cat item details and you're off an running.
The Oracle cost-based optimizer makes use of all the information that it has to decide what the best access paths are for the data and what the least costly methods are for getting that data. So below are some random points related to your question.
The first three tables that you've listed all have primary keys. Do the other tables (catalog_university and catalog_securitygroup) also have primary keys on them?? A primary key defines a column or set of columns that are non-null and unique and are very important in a relational database.
Oracle generally enforces a primary key by generating a unique index on the given columns. The Oracle optimizer is more likely to make use of a unique index if it available as it is more likely to be more selective.
If possible an index that contains unique values should be defined as unique (CREATE UNIQUE INDEX...) and this will provide the optimizer with more information.
The additional indexes that you have provided are no more selective than the existing indexes. For example, the index on (catalog.id, catalog.name, catalog.owner) is unique but is less useful than the existing primary key index on (catalog.id). If a query is written to select on the catalog.name column, it is possible to do and index skip scan but this starts being costly (and most not even be possible in this case).
Since you are trying to select based in the catalog.root column, it might be worth adding an index on that column. This would mean that it could quickly find the relevant rows from the catalog table. The timing for the second query could be a bit misleading. It might be taking 2 seconds to find 50 matching rows from catalog, but these could easily be the first 50 rows from the catalog table..... finding 50 that match all your conditions might take longer, and not just because you need to join to other tables to get them. I would always use create table as select without restricting on rownum when trying to performance tune. With a complex query I would generally care about how long it take to get all the rows back... and a simple select with rownum can be misleading
Everything about Oracle performance tuning is about providing the optimizer enough information and the right tools (indexes, constraints, etc) to do its job properly. For this reason it's important to get optimizer statistics using something like DBMS_STATS.GATHER_TABLE_STATS(). Indexes should have stats gathered automatically in Oracle 10g or later.
Somehow this grew into quite a long answer about the Oracle optimizer. Hopefully some of it answers your question. Here is a summary of what is said above:
Give the optimizer as much information as possible, e.g if index is unique then declare it as such.
Add indexes on your access paths
Find the correct times for queries without limiting by rowwnum. It will always be quicker to find the first 50 M&Ms in a jar than finding the first 50 red M&Ms
Gather optimizer stats
Add unique/primary keys on all tables where they exist.
The use of rownum is wrong and causes all the rows to be processed. It will process all the rows, assigned them all a row number, and then find those between 0 and 50. When you want to look for in the explain plan is COUNT STOPKEY rather than just count
The query below should be an improvement as it will only get the first 50 rows... but there is still the issue of the joins to look at too:
SELECT ccc.* FROM (
SELECT cc.*, ROWNUM AS n FROM (
SELECT c.id, c.name, c.owner
FROM catalog c
WHERE c.root = 100
ORDER BY name
) cc
where rownum <= 50
) ccc WHERE ccc.n > 0 AND ccc.n <= 50;
Also, assuming this for a web page or something similar, maybe there is a better way to handle this than just running the query again to get the data for the next page.
try to declare a cursor. I dont know oracle, but in SqlServer would look like this:
declare #result
table (
id numeric,
name varchar(255)
);
declare __dyn_select_cursor cursor LOCAL SCROLL DYNAMIC for
--Select
select distinct
c.id, c.name
From [catalog] c
inner join university u
on u.catalog = c.id
and u.university = 300
inner join catalog_securitygroup s
on s.catalog = c.id
and s.securitygroup = 200
Where
c.root = 100
Order by name
--Cursor
declare #id numeric;
declare #name varchar(255);
open __dyn_select_cursor;
fetch relative 1 from __dyn_select_cursor into #id,#name declare #maxrowscount int
set #maxrowscount = 50
while (##fetch_status = 0 and #maxrowscount <> 0)
begin
insert into #result values (#id, #name);
set #maxrowscount = #maxrowscount - 1;
fetch next from __dyn_select_cursor into #id, #name;
end
close __dyn_select_cursor;
deallocate __dyn_select_cursor;
--Select temp, final result
select
id,
name
from #result;