I have a materialized view that brings back 2 columns and roughly 300m rows.
The materialized view is based on joins between multiple views.
Currently it takes roughly 10 minutes for this to refresh and I am trying to improve the refresh time since there are usually very few changing records in this data set.
I currently run a "Complete" refresh - is there a way to run a fast refresh since this materialized view is based on other views and not tables?
Thank you
See https://docs.oracle.com/database/121/DWHSG/basicmv.htm#i1007007 for fast refresh requirements and limitations.
Use DBMS_MVIEW.EXPLAIN_MVIEW for analyzing your materialized view query to see why the fast refresh is not possible to use.
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We are using Oracle Materialized view to extract data for a reporting system. The setting of the MV is to refresh on every commit.
After migrating to Oracle 19 form Oracle 12 system was very slow for few days and eventually became unresponsive after few days due to various bugs in Oracle 19 related to Materialized View.
We did a workaround of changing MV setting from on commit to OnDemand every 5 min to solve this issue.
The parent table on which this view is created gets updated every second and has 2 million records.
Having a MV on a table which is updated so frequently is fundamentally not a good design.
We don't want to depend on Oracle patches to fix this and planning to redesign this table.
Can I change this view to simple view and possibly apply all possible ways to improve query response time and expect that I will have view query returned in few seconds given I have 2 mil records in Parent table.
Assume that table has basic datatypes only and view is reading about 5-6 fields.
We tried oncommit to ondemand as a workaround but as per the business need, we need committed data for the reporting system and cannot be delayed more than one min.
In our oracle query, I used materialized view to improve the performance and saw a drastic change in performance time of query, response time is in .17 seconds now rather 30 seconds so its working in case we are working on historical data set and need to have one time refresh of materialized view but now requirement is if base table of materialized view would be updating frequently in that case it would be working as the refresh activity of materialized view would be consuming time as well, currently the base table has around 170000 records but in future definitely going to increase so is there any solution or option to resolve this. As i have tried to apply Indexes as well on the table but not able to achieve response time within .17 sec or around the last response time based on index creation was 18 sec.
Looking into getting near-realtime analytics data from bigquery, and considering costs vs. accuracy, it seems like using materialized view might be a great win.
Considering "near real time" will change to a minimum of 1 minute refresh_interval_minutes, my main concern is that while from documentation it seems that the query will be only on the delta data, the billing will be on the "standard" minimum of 10MB per table.
As I see it, if this minimum is being forced, it dismiss using materialized view as a valid solution for near-realtime.
I would have used "standard" caching over the queries, but caching does not work when querying table with "buffered data", as far as I understand it.
Please advise,
Shushu
The following are key characteristics of BigQuery Materialized Views:
Zero maintenance: A materialized view is recomputed in background once the base table has changed. All incremental data changes from the base tables are automatically added to the materialized views. No user inputs are required.
In other words it means that incremental changes like streaming data into, is automatically added to the materialized view. That means you don't need to set 1 minute refresh period. The maximum refresh frequency cap is 7 days. You could set it to 7 days, or even disable manual refresh as you don't have deletes.
I have an Oracle materialized view refreshed on demand. Since the view is pretty large, it takes a while to update. I am wondering: when do the updates really become visible to the queries that try read the view? Does RDBMS update the view in a buffer and then makes it visible when update is complete? Or will the changes gradually become visible to the reader? Is this possible to control this?
Materialized views can be refreshed on commit or on demand.
Oracle's documentation is quite good
https://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_6002.htm#i2116410
To have materialized views refresh incrementally you must use the FAST option and you must have materialized view logs to capture changes on the source tables.
If you schedule the demanded refreshes frequently there will be less work to be done for each refresh. If you schedule them less frequently there will be more work to be done. You need to investigate how changes on the source tables are distributed over time to choose well.
Changes will be visible to users when the refresh (whatever size) commits.
I have materialized view in my own schema and the materialized view source is the other schema table but , this master table has 900 rows and i did some dml operations on this master table after that i will refresh this materialized view as you know , and i did some resarch " how can i refresh my own materialized view " and it says " you can do complete refresh or fast refresh " but i didnt understand these solutions meaning so my question is simple ;
What is the difference between complete refresh and fast refresh in MV ?
P.S:If my master table has 1 million or more rows , which one i should choose? (fast or complete)
Thank you for your reply.
"Complete Refresh" means you truncate entire materialized view and insert new data.
"Fast Refresh" means you update (or insert/delete) only the rows which have been changed on master tables.
And just as information "Force Refresh" mean, Oracle tries to make a Fast Refresh and if this is not possible then do "Complete Refresh"
Usually Fast Refresh is much faster than Complete Refresh but it has restrictions. You have to define MATERIALIZED VIEW LOG on master tables.
Here is a full list of restrictions General Restrictions on Fast Refresh, there are quite many.
As always it depends, so if possible try both and measure for your application. As a general rule the fast refresh is likely to be much faster provided that only a small part of the data has changed. If all the data has changed a complete refresh is better.
With the fast refresh Oracle keeps track of the changes for the base tables and applies the changes to the materialized view when it is refreshed. A complete refresh on the other hand rebuilds the materialized view from scratch. With millions of rows that will be expensive, but again it is impossible to pick the best option without knowing more about your application.