experience w/ UUID's for surrogate keys across entire schema?

From: Chris Stephens <cstephens16_at_gmail.com>
Date: Thu, 13 Sep 2018 16:17:19 -0500
Message-ID: <CAEFL0syPPJzhv2F8UyNA27kQBfJtyY2L4wJ5Djh2hAggETMKpw_at_mail.gmail.com>

we have an application that will be deployed at an unknown number of locations. the application requires the ability to ingest data from every location into a central repository. the application will also store data in non-oracle databases at some locations. all locations will have the same schema. all surrogate keys for all tables across all locations have to be unique. some of these locations running Oracle will be "small" and some will require beefy RAC systems to support the workload.

2 methods of satisfying this requirement are being considered:

1. use a multi-column or concatenated column PK with some sort of "site id" + sequence based values for oracle systems and figure out the equivalent in the other database products. To allow for scalability on busy RAC systems I currently plan to recomment a site_id + inst_id + mod(session_id, <some number>) + sequence value.
2. use UUID's generated in the application code for all surrogate keys everywhere.

I'm being asked to weigh in on the advantages/disadvantages of both. Option 1 is ideal from an Oracle perspective if performance is primary concern (there will be locations that will stress any hardware we throw at it). Option 2 is preferred by the developers and I think is functionally fine.

I think the primary concern for option 2 is the completely random nature of UUIDs and the fact that all these PK/Unq indexes will need to be fully cached to maintain performance which will stress oracle's buffer management and result in far more physical I/O for inserts as well as for other database activity that gets aged out of buffer cache. I have explained that concern as best I can but the developers are (justifiably asking for more concrete answers other than "this will likely become a problem at some point if the application activity exceeds the ability of Oracle, on the current hardware, to maintain active blocks in the buffer cache". I am going to try and come up with a test to demonstrate the degraded performance on our current 3-node 12.2 RAC system (child's play for what eventual production and test systems will be). Does anyone have suggestions on how to best set up that test and demonstrate the downfalls of UUID approach at some currently unknown scale? Also, does anyone have any experience using externally generated UUID's as surrogate keys in Oracle? Good/bad/indifferent?

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I'm most certainly reaching out to oracle-l more than ever before as these are problems I've never had to deal with and truly appreciate all the people that take the time to chime in.

Thanks!
Chris

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Received on Thu Sep 13 2018 - 23:17:19 CEST