I'm looking for some advice for a system that has a "dry run" mode that will be used to help with the QA of data transformations. The idea is to be able to log and report what would happen to the database and then apply that log if not in dry run mode.
We've considered creating a sort of common format csv file but that has limited us. My other thought was to log the sql inserts/updates/deletes so we can view them in dry run and apply them in production mode, but that certainly adds work and the concern regarding sql injection (though I can use parameterized queries).
What would be ideal is to use something within postgres, such as using rollback transactions but then get the sql output from within those transactions.
Has anyone had to solve for something like this? Is this kind of a pipedream that may be more trouble than it's worth?
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I often have to execute complex sql scripts in a single transaction on a large PostgreSQL database and I would like to verify everything that was changed during the transaction.
Verifying each single entry on each table "by hand" would take ages.
Dumping the database before and after the script to plain sql and using diff on the dumps isn't really an option since each dump would be about 50G of data.
Is there a way to show all the data that was added, deleted or modified during a single transaction?
Dude, What are you looking for is the most searchable thing on the internet when it comes to capturing Database changes. It is a kind of version control we can say.
But as long as I know, sadly there are no in-built approaches are available in PostgreSQL or MySql. But you can overcome it by setting/adding some triggers for your most usable operations.
You can create some backup schemas, and tables to capture your changes that are changed(updated), created, or deleted.
In this way you can achieve what you want. I know this process is fully manual, But really effective.
If you need to analyze the script's behaviour only sporadically, then the easiest approach would be to change server configuration parameter log_min_duration_statement to 0 and then back to any value it had before the analysis. Then all of the script activity will be written to the instance log.
This approach is not suitable if your storage is not prepared to accommodate this amount of data, or for systems in which you don't want sensitive client data to be written to a plain-text log file.
Recently I've been asigned to migrate part of the database from Oracle to PostgreSQL enviroment, as testing experiment. During that process, major drawback that occured to me was lack of simple way to implement parallelism which is required due to multiple design reasons, which aren't so relevant here. Recently I've discovered https://www.postgresql.org/docs/11/bgworker.html following process, which occured to me as some way to solve my problems.
Yet not so truly, as I couldn't easly find any tutorial or example how to implement it even for a simple task as writing debugmessages into logger, while the process is running. I've tried some old ways, presented in some plugin specifications from version 9.3, but they weren't much of help.
I would like to know how to set up those workers properly. Any help would be appriciated.
PS: Also if some good soul found workaround to implement bulk collect for cursors into PostgreSQL it would be most kind of you, to share it.
The documentation for bgworker that you linked to is for writing C code, which is probably not what you want. You can use the pg_background extension, which will do what you want. ora2pg will optionally use pg_background when converting oracle procedures with the autonomous transaction pragma. The other option is to use dblink to open a connection to the current db.
Neither solution is great, but it's the only way to go if you need to store data in a table whether or not the enclosing transaction succeeds. If you can get by with just putting stuff into the logs, you can use RAISE NOTICE instead.
As far as bulk collect for cursors go, I'm not sure exactly how you are using them, but set returning functions may help you. Functions in postgres can return multiple rows without fiddling with cursors.
I have taken over an existing MVC website which uses entity framework and hangfire and is hosted on Azure and uses Azure database. Every so often the website times out.
I'm new to Azure portal, entity framework and hangfire.
If I increase the DTU's it clears the timeout issues?
I'm looking for ways of how to diagnose why the website times out. I have added error logging using elmah and checked hangfire but this doesn't give me any further information.
Is there anything in azure portal that can help?
If it "times out" and if "increasing DTU resolves timeouts" and these observations are true (I think it's on you to really convince yourself this is absolutely true, don't make this assumption lightly) then the usual and obvious candidate is "a slow sql query". Entity Framework is often used with linq to create sql queries without writing sql. These queries are often fine for very simple tasks, such as someData.Where(x=>x.Id == 1).First(), however, if linq is used to join tables, or create complex associations, the generated sql can become monstrously bad, from a performance perspective. You can add logging to write out the sql generated by linq, or you can try to trace the database to see what sql is running on it. If tracing is out of the question, there are still meta queries you can use to view things like cached query plans and SQL Server can give you estimated costs and cached execution counts.
You can still hang yourself without using linq. You can still use stored procedures with EF. Way too many developers are naive about SQL performance still; you need to comb over your back end and learn the schema, the stored procedures; inspect the sql contents of everything. Check for any database triggers (easy to miss). Red flags are subqueries, too many joining, too many results from a query, lots of string manipulation in a query, joining tables on strings, or XML/JSON-based SQL work.
Be aware that "slow sql queries" will become slower when load is high. And when slow sql queries build up, they only take more time to resolve. This can also cause debilitating table locking, depending on the nature of the query.
But queries can be performant and still cause locking. ie One table is being written to often and it's blocking other writes or reads from that table. This is a little harder to diagnose, but you can figure it out by carefully inspecting logs of database calls and how long they take to execute. There are also sql queries you can run on the database to diagnose long-running queries, or what tables are locked at a given point in time.
Finally, check for any back end webjobs for your application. If timeouts occur at reoccurring days or times, then somebody's batch SQL could be blocking your production database from being read.
But this is all speculation. I think you need to do more research to determine what is actually causing the site to become unresponsive. If you can log response times for common queries, you can rule out SQL-based latency as being the culprit or not and work from there. There's nothing inherently "amiss" about any of the technologies you specified.
If queries are perfomant but still causing issues, a long term solution is to add something like a message queue and batch your sql work intelligently, or just make the database work asynchronous and not block the UI.
You should correlate any logged timeouts with azure's monitoring. Azure can give you CPU/RAM/page visits and such on the dashboard.
SQL Azure is a bit of a different beast. It doesn't have the on-demand performance of a dedicated DB unless you're prepared to throw serious $$ at it. And even then ...
EF, when written for well can perform quite well. When written poorly it can be a dog, and those problems are compounded on a platform like SQL Azure.
The first thing is to check that your EF contexts are set up to use an execution strategy suited to Azure: https://learn.microsoft.com/en-us/ef/ef6/fundamentals/connection-resiliency/retry-logic
The next thing would be to see what kinds of SQL tracing you can run on Azure. Tracing is essential to see what EF is doing behind the scenes. I'm not familiar with tools available for Azure, in my case my Azure experience was running SQL Server on VMs because SQL Azure was too immature, not HIPAA compliant at the time, and expensive for the DTU estimates we were able to get. Worst case, can you restore an database backup into an SQL Server instance and point a copy of your application environment temporarily at that to run through common usage scenarios? Using an SQL Trace you can pick up on exactly when and how often EF is executing queries, and what queries it is executing.
Things to look at:
How many queries are running? If you are loading a set of records and expect one query, are there a whole heap of queries getting sent? This would indicate lazy-load calls being triggered.
What queries are being run? Is it selecting a lot more fields than are being displayed? This would be potentially a case where entire entities are being loaded where a .Select() could be used to reduce the amount of data. Perhaps even the case where entire sets of entities are being loaded that aren't relevant to what is displayed/done, such as cases where someone is using .ToList() prior to just doing a .Count() or .Any() or doing a .FirstOrDefault() just to do a != null check.
Is the database properly indexed? Copy some of the heavier queries into SQL Manager and execute them with an execution plan. Are there indexing suggestions?
The common sins of developing with EF and other ORMs boil down to "pulling too much, too often." It's surprising how many clients I've worked with have development teams that have not used a profiler to inspect their ORM use efficiency. (and I'm talking 0% so far.)
I am working on a project where i want to give people the possibility to execute SQL queries on an PostgreSQL database. I then only need to prevent people from hacking/attacking my database.
I thought that maybe a way to do that, is by giving only view access to de database connection. And using EXPLAIN ANALYSE to calculating the cost of the SQL query.
Is EXPLAIN ANALYSE trustworthy enough to make sure there are no cheap ways to get the website down?
Do you have suggestions?
EXPLAIN ANALYSE will execute the query, including any side-effects it may have. PostgreSQL also allows running arbitrary Perl and Python code if configured to do so, so be careful. You're likely better off running PostgreSQL instances in per-request VMs or in similar highly isolated environments.
We're considering using SSIS to maintain a PostgreSql data warehouse. I've used it before between SQL Servers with no problems, but am having a lot of difficulty getting it to play nicely with Postgres. I’m using the evaluation version of the OLEDB PGNP data provider (http://www.postgresql.org/about/news.1004).
I wanted to start with something simple like UPSERT on the fact table (10k-15k rows are updated/inserted daily), but this is proving very difficult (not to mention I’ll want to use surrogate keys in the future).
I’ve attempted (Link) and (http://consultingblogs.emc.com/jamiethomson/archive/2006/09/12/SSIS_3A00_-Checking-if-a-row-exists-and-if-it-does_2C00_-has-it-changed.aspx) which are effectively the same (except I don’t really understand the union all at the end when I’m trying to upsert) But I run into the same problem with parameters when doing the update using a OLEDb command – which I tried to overcome using (http://technet.microsoft.com/en-us/library/ms141773.aspx) but that just doesn’t seem to work, I get a validation error –
The external columns for complent.... are out of sync with the datasource columns... external column “Param_2” needs to be removed from the external columns.
(this error is repeated for the first two parameters as well – never came across this using the sql connection as it supports named parameters)
Has anyone come across this?
AND:
The fact that this simple task is apparently so difficult to do in SSIS suggests I’m using the wrong tool for the job - is there a better (and still flexible) way of doing this? Or would another ETL package be better for use between two Postgres database? -Other options include any listed on (http://en.wikipedia.org/wiki/Extract,_transform,_load#Open-source_ETL_frameworks). I could just go and write a load of SQL to do this for me, but I wanted a neat and easily maintainable solution.
I have used the Slowly Changing Dimension wizard for this with good success. It may give you what you are looking for especially with the Wizard
http://msdn.microsoft.com/en-us/library/ms141715.aspx
The External Columns Out Of Sync: SSIS is Case Sensitive - I encountered this issue multiple times and it makes me want to pull my hair out.
This simple task is going to take some work either way. SSIS is by no means an enterprise class ETL product yet, but it does give you some quick and easy functionality, and is sufficient for most ETL work. I guess it is also about your level of comfort with it as well.
SCD is way too slow for what I want. I need to use set based sql.
It turned out that a lot of my problems were with bugs in the provider.
I opened a forum topic (http://www.pgoledb.com/forum/viewtopic.php?f=4&t=49) and had a useful discussion with the moderator/support/developer person.
Also Postgres doesn't let you do cross db querys, so I solved the problem this way:
Data Source from Production DB to a temp Archive DB table
Run set based query between temp table and archive table
Truncate temp table
Note that the temp table is not atchally a temp table, but a copy of the archive table schema to temporarily stored data in.
Took a while, but I got there in the end.
This simple task is going to take some work either way. SSIS is by no means an enterprise class ETL product yet, but it does give you some quick and easy functionality, and is sufficient for most ETL work. I guess it is also about your level of comfort with it as well.
What enterprise ETL solution would you suggest?