[keycloak-dev] Database types for primary and foreign keys

Mon Dec 19 05:34:21 EST 2016

I'm not convinced that the proposed changes would make a significant
difference in performance. We heavily cache things and complicated queries
are usually limited to admin operations. That being said if we can do a POC
to check the performance it may be worth it, especially with large number
of entries (we recently had someone talking about 150 million users!).

As Bill points out is has to be backwards compatible and it has to be
possible to automatically perform the changes to the database. From talking
to Hynek it seems like this may be possible. Since the User Storage SPI is
being supported in RHSSO 7.1 there's also no option for us to make changes
to this, but it doesn't seem like we'd have to.

This is something that is worth considering to investigate more at some
point (first step would be to evaluate the real benefits if any), but when
we can prioritize is another question.

On 16 December 2016 at 21:30, Bill Burke <bburke at redhat.com> wrote:

> Not every key is a simple UUID.  Specifically any table that references
> a user:  UserFederatedStorageProvider tables and offline tokens.  THis
> is because of the user storage spi.  These tables must be searchable by
> user id which can either be a UUID (keycloak database) or  "f:" +
> componentUUID + ":" + opaque_external_identifier (External User Storage
> Provider database).  So breaking up a User Storage SPI USER_ID isn't
> going to help as you'll still need to create an index based on these
> columns.  Also, there's been some talk of using this ID format for other
> model types like Roles and Groups.
>
> Also, Everything has to remain backward compatible.  We will need to
> support existing databases.  So, can you support changing to a
> completely different id format and type without screwing up existing
> databases???  I don't think doing a full export/import to/from JSON is
> going to work with large deployments.  Will this @Nationalize Hibernate
> annotation allow us to turn off the SQl Server implicit unicode
> conversion and send everything via ascii by default?
>
> Finally, I'm going to freak if I have to do a lot of refactoring to the
> User Storage SPI.  A solution that keeps existing user storage and SPIs
> backward compatible with very little work on the backend should be made
> a  priority instead of completely rearchitecting something so
> fundamental to our datamodel.
>
>
> On 12/16/16 2:12 PM, Hynek Mlnarik wrote:
> > Hi All,
> >
> > Apologies for a long e-mail.
> >
> > TLDR: We need to define format of primary keys (UUID) so that it is
> possible to transform the primary and foreign keys from VARCHAR(36) columns
> into database-native binary format. This is in particular important to
> document in 2.5 in Storage Ids section of the new User Storage SPI [1]
> >
> > Long version:
> >
> > I have looked at current database model and while generally it looks
> well, there is an interesting issue with primary / foreign keys that causes
> performance degradation on both Java and - most importantly - database
> side, causing even deadlocks for some databases.
> >
> > The issue comes from database handling of IDs. IDs are in fact UUIDs,
> i.e. series of bytes that are represented by Strings in KC JPA classes. Why
> this causes performance degradation is due to various representations
> conversions (byte array vs String in Java) and - most importantly for
> database - character set conversions. In the worst case, The conversions
> occur both in JDBC driver and the database. The consequences are
> demonstrated by Jira issue KEYCLOAK-3210 [2] when several simultaneous
> requests lead to deadlocking the database.
> >
> > When JDBC driver obtains a string, it converts its representation into a
> character set understood by database. Database might need to convert the
> string to a character set specified for the column. This is nicely
> illustrated in MSSQL which makes distinction between VARCHAR (8-bit
> codepages) and NVARCHAR (UCS-2 Unicode charset). IDs are VARCHARs which is
> indeed an efficient way to use strings that consist of ASCII-only
> characters (though not optimal for UUID, read below). However, if Unicode
> characters are to be supported, MSSQL JDBC driver sends all character
> parameters as Unicode Strings [3]. Database then performs a conversion from
> Unicode to 8-bit charset which generally loses some data. To account for
> this loss, instead of performing an index scan that directly points to a
> requested row, it returns a range where the requested record should be.
> This has fatal impact on performance. For more detailed analysis of the
> resulting plans, see comment in [2].
> >
> > Clearly, the scan by id should be fast and the format of IDs in database
> matters. It should avoid conversions as much as possible. Hence the
> following plan came:
> >
> > * In the result, all primary keys and corresponding keys have to be
> represented by binary UUID data type (where supported, some databases
> represent UUID as e.g. VARBINARY(16)), i.e. 16 bytes instead of 36 bytes
> > * All keys in the JPA classes should be of type UUID, not String
> >
> > As a result, database indices get smaller (16 bytes of indexed data per
> record vs 36 bytes as it is now in case of 8-bit storage of characters),
> and no character conversions are in place, hence the overall performance
> increases.
> >
> > This task is a slighty big one so it won't fit into KC 2.5 timeframe,
> but we should definitely aim for 3.0.
> >
> > This has several preconditions:
> > * The String keys in keycloak JPA classes, wherever used, are restricted
> to UUID format
> > * This format is documented and respected by all custom implementations,
> namely User Storage implementations.
> > * There exists conversion from String to native UUID for used databases
> (this is certainly possible for PostgreSQL MSSQL, DB2, and MySQL, most
> likely others)
> >
> > Similarly to JPA, Infinispan classes should be revisited and optimized
> to save some bytes that might be important for cluster replication by
> replacing String with UUIDs
> >
> > Thoughts?
> >
> > --Hynek
> >
> > [1] https://github.com/keycloak/server_development_guide/blob/
> 6b82f0868c0d7a148a084a30e0d8fda192f01502/topics/user-
> storage/model-interfaces.adoc
> > [2] https://issues.jboss.org/browse/KEYCLOAK-3210
> > [3] https://msdn.microsoft.com/en-us/library/ms378857(v=sql.110).aspx
> >
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