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Daniel Westermann

What that in-memory term is about, and what not

By | Database management | No Comments

Everybody is talking about in-memory databases these days. And everybody is talking about columnar store for sets of data because this can be a benefit for analytic queries. And a lot of people start mixing these terms not realizing that these topics are not exchangeable. Traditionally in-memory means: Not persistent, but fast. And this is what pure in-memory databases are: Not persistent, but fast, but, again: not persistent!!! They are just caching data for very…

 
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Matthieu Munch

Row Store vs Column Store in SAP HANA

By | Development & Performance | One Comment

The SAP HANA database allows you to create your tables in Row or Column Store mode. In this blog, I will demonstrate that each method has its advantages and disadvantages and should be used for specific cases. Thanks to two kind of tests, I will show you that the Row Store mode should be used for simple SELECT SQL queries, without aggregation and the Column Store mode should be used for complex SELECT queries, containing…

 
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David Barbarin

Variations on 1M rows insert (3): using SQL Server In-Memory features

By | Development & Performance | No Comments

Let’s continue with this series about inserting 1M rows and let’s perform the same test with a new variation by using SQL Server In-Memory features. For this blog post, I will still use a minimal configuration that consists of only 1 virtual hyper-V machine with 1 processor, 512MB of memory. In addition my storage includes VHDx disks placed on 2 separate SSDs  (one INTEL SSDC2BW180A3L and one Samsung SSD 840 EVO). No special configuration has…

 
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Franck Pachot

Variations on 1M rows insert (4): IN MEMORY

By | Database management, Oracle | No Comments

Oracle In-Memory option is for reporting. Oracle has chosen an hybrid approach: maintain the In-Memory Column Store in addition of the buffer cache. Dont’ forget our In-Memory event, but for the moment, let’s try the 1M row insert when the target table is IN MEMORY. 12c I’ve done the previous variations on 11g because I wanted to use the Developer Days VM that has also TimesTen installed. But now I want to test some 12c…

 
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Stéphane Savorgnano

In-Memory OLTP: Hash and Range indexes

By | Hardware & Storage | No Comments

Since SQL Server 2014 CTP2, Microsoft has introduced a new kind of index which is the Range index. We have now two ways for indexing an In-Memory table: using either an Hash index or a Range index. These two indexes are slightly different. In fact, a Hash index is a set of buckets, 8-bytes memory pointers, which points to the actual row data or row chain data. SQL Server 2014 uses a hash function to…

 
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Stéphane Haby

SQL Server Tips: How to know if In-Memory Feature is supported by your server?

By | Database management | No Comments

A customer asks me, how to know if In-Memory Feature is supported by my SQL Server server? An easy way is to check the edition, version etc. but now, you have directly a property for that. On msdn here, you find all property that you can search with the T-SQL Command: SERVERPROPERTY But if you try to run through all your servers with CMS (Central Management Server), for all SQL Server below than SQL Server…

 
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Franck Pachot

ALTER TABLE INMEMORY

By | Database management, Oracle | No Comments

In-Memory Column Store is amazing. It brings very good performance to full table scans. I’t easy: just ‘flip a switch’ and you accelerate all reporting queries on your table, without thinking about what to index and how. But in this post, I would like to warn you about the consequences when you just flip that switch. The new full table scan plan will replace the old ones… even before the table is populated in memory……

 
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David Barbarin

Memory management, OOM issues with SQL Server 2014 In-memory OLTP

By | Application integration & Middleware | No Comments

Last week I gave a workshop about SQL Server 2014 and the new features. The first day we worked on new In-memory OLTP and different topics such as the new internal storage, the new transaction processing behavior or the new checkpointing process. During this day, one of the attendees asked me about the memory management with In-Memory OLTP feature. It was a very interesting question but unfortunately I didn’t have the time to discuss about…

 
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Franck Pachot

Oracle 12.1.0.2: Wait event histograms in μs

By | Database Administration & Monitoring, Oracle | 2 Comments

When an Oracle Database spends a high percentage of its DB time in User I/O, I usually check the wait event histograms in order to see if the storage system is working well. But today, with storage going to SSD, most I/O are less than 1 milliseconds and we have no details about those wait times. Here is what is exposed by V$WAIT_EVENT_HISTOGRAM:   select event,wait_time_milli,wait_count from v$event_histogram where event like ‘db file sequential read’…

 
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Franck Pachot

Beyond In-Memory, what’s new in 12.1.0.2 ?

By | Database management, Oracle | No Comments

It’s just a patchset. The delivery that is there to stabilize a release with all the bug fixes. But it comes with a lot of new features as well. And not only the one that has been advertised as the future of the database. It’s a huge release. Let’s have a look at what’s new. First, it seems that it will be the only patchest for 12.1 Then, there is that In-Memory option awaited for…

 
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