I am trying to update statistics to some of our tables whose names I receive as input to my procedure. But, I couldn't compile the procedure with the below code.
update index statistics #tableName
Aren't dynamic table names allowed? Or, would the below statement work?
select #statsCmd = 'update index statistics '+#tableName
exec(#statsCmd)
Also, what are the notable differences between "update statistics" and "update index statistics"?
It does appear that update statistics does not allow dynamic table names, but the second statement should work without issue.
Regarding update statistics & update index statistics:
Update statistics can be run against tables without indexes, and other non-index objects, as well as against indexes. If run against an index, it actually executes an update index statistics behind the scenes. Update index statistics only updates statistics for the indices on the specified table.
Also, have you looked into using the Job Scheduler, and the datachange function to automate your update statistics?
Related
I need clarification on how DBMS_STATS.GATHER_TABLE_STATS works.
I have a scenario,were i am creating table and the same table is used in the package creation also.In other words the package compilation is depended on table creation.
Is it mandatory to include DBMS_STATS.GATHER_TABLE_STATS after index creation command in table creation script.
In which situation DBMS_STATS.GATHER_TABLE_STATS works,whether it's for package compilation or package execution.Please confirm.
DBMS_STATS provides information to the Oracle optimizer, enabling Oracle to build efficient execution plans for SQL statements. Optimizer statistics are never necessary for compiling objects.
Gathering statistics is such a complicated subject it can be difficult to even ask the right questions at first. I'd recommend starting by reading the manual, such as Managing Optimizer Statistics: Basic Topics.
Typically your statistics gathering strategy should look something like this:
Gather statistics manually whenever an object's data significantly changes.
Use the default autotask to automatically gather statistics for objects that have been slowly changing or were accidentally forgotten.
To answer some specific questions, you probably do not want to gather statistics right after creating a table. Only gather statistics after changing the data. Gathering statistics on an empty table can be dangerous; Oracle will think the table has 0 rows until the next time statistics are gathered. It would be better to have no statistics at all, then Oracle can use dynamic sampling to estimate the statistics.
(But on the other hand, if the table is created as a SELECT statement and contains a lot of data you may want to gather statistics. Then again, if you're using 12c it might gather statistics automatically when creating a table.)
You also generally do not need to gather statistics after creating an index. Oracle automatically gathers index statistics when an index is created or rebuilt.
I am not an expert of oracle, I just write queries and scripts through TOAD but I don't know how oracle works.
In order to make a data analysis I have created several tables in order to build a DB from them.
In order to build them I have used the following command
CREATE TABLE SCHEMA.NAME
TABLESPACE SCHEMASPACE NOLOGGING PARALLEL AS
select [...]
with the parallel option active in order to make the server work on more processors.
Once that the DB was created I have tried to do some queries on it but the same query done on the same DB 2 times gave me two different answers. In detail the first time I started the query it returned to me a table with about 2500 rows and the second time it returned to me a table with about 2650 rows.
I have tried to redo the entire process without the parallel option and now it seems to work, but it take too much time and I need to run the process several times, does anyone have a solution?
I just created a new table on 11gR2 and loaded it with data with no index. After the loading was completed, I created several indexes on the new table including primary constraint.
CREATE TABLE xxxx (col1 varchar2(20), ...., coln varhcar2(10));
INSERT INTO xxxx SELECT * FROM another_table;
ALTER TABLE xxxx ADD CONSTRAINT xxxc PRIMARY KEY(col_list);
CREATE INDEX xxxx_idx1 ON xxxx (col3,col4);
AT this point do I still need to use DBMS_STATS.GATHER_TABLE_STATS(v_owner,'XXXX') to gather table stats?
If yes, why? since Oracle says in docs "Oracle Database now automatically collects statistics during index creation and rebuild".
I don't want to wait for automatic stats gathering over night because I need to report the actual size of the table and its index immediately after the above operations. I think running DBMS_STATS.GATHER_TABLE_STATS may give me a more accurate usage data. I could be wrong though.
Thanks in advance,
In Oracle 11gR2 you still need to gather table statistics. I guess you read documentation for Oracle 12c, which automatically collects the statistics but only for direct path inserts, which is not your case, your insert is conventional. Also if you gather statistics (with default options) for brand new table that hasn't been used for queries no histograms will be generated.
Index statistics are gathered when index is built so it's not needed to gather its statistics explicitly. When you later gather table statistics you should use the DBMS_STATS.GATHER_TABLE_STATS option cascade => false so that index statistics aren't gathered twice.
You can simply check the statistics using
SELECT * FROM ALL_TAB_COL_STATISTICS WHERE TABLE_NAME = 'XXXX';
In ODI we used the DBMS_STATS.GATHER_SCHEMA_STATS to recompute the stats only when a table changed by a certain percentage with the option (options => 'GATHER AUTO'). (http://docs.oracle.com/cd/B19306_01/appdev.102/b14258/d_stats.htm#i1036456)
Now I want to move the calculation of statistics to the table level (in the IKL) but DBMS_STATS.GATHER_TABLE_STATS does not seem to have a setting to only recompute the stats if they need an update (determined by Oracle).
(http://docs.oracle.com/cd/B19306_01/appdev.102/b14258/d_stats.htm#i1036461)
Always recomputing the statistics of all our tables is too costly.
Does anyone know a way to check if a table needs its statistics updated or a hidden option in DBMS_STATS.GATHER_TABLE_STATS.
DBMS_STATS.GATHER_SCHEMA_STATS has an option to LIST STALE objects; you could run that first and decide if your table is in the list of returned objects.
Check the column STALE_STATS from USER_TAB_STATISTICS / ALL_TAB_STATISTICS / DBA_TAB_STATISTICS
I have a table containing 50M records and I have to update almost all of it. I want to use parallel update on the table. Which will be faster, having indexes on the table or without?
If you're going to update almost all of the table, then I suspect the access method used will be a full table scan - which means the indexes won't be used to speed up the queries.
Therefore, the only impact that indexes may have will be the extra work required to maintain them for the update - so the more indexes, the slower your update will be.