2009-03-13 06:14:52 UTC
1. Subqueries are poorly optimized.
2. Complex queries are a weak point.
3. The query executioner (aka query optimizer / planner) is less
4. Performance tuning and metrics capabilities are limited.
5. There is limited ability to audit.
6. Security is unsophisticated, even crude. There are no groups or roles,
no ability to deny a privilege (you can only grant privileges). A user who
logs in with the same username and password from different network addresses
may be treated as a completely separate user. There is no built-in
encryption comparable to Oracle.
7. Authentication is built-in. There is no LDAP, Active Directory, or
other external authentication capability.
8. Clustering is not what you think it is.
9. Stored procedures and triggers are limited.
10. Vertical scalability is poor.
11. There is zero MPP support.
12. SMP is supported, but MySQL doesnt scale well to more than 4 or 8
13. There is no fractional-second storage type for times, dates, or
14. The language used to write stored procedures, triggers, scheduled
events, and stored functions is very limited.
15. There is no roll-back recovery. There is only roll-forward recovery.
16. There is no support for snapshots.
17. There is no support for database links. There is something called the
Federated storage engine that acts as a relay by passing queries along to a
table on a remote server, but it is crude and buggy.
18. Data integrity checking is very weak, and even basic integrity
constraints cannot always be enforced.
19. There are very few optimizer hints to tune query execution plans.
20. There is only one type of join plan: nested-loop. There are no
sort-merge joins or hash joins.
21. Most queries can use only a single index per table; some multi-index
query plans exist in certain cases, but the cost is usually underestimated
by the query optimizer, and they are often slower than a table scan.
22. There are no bitmap indexes. Each storage engine supports different
types of indexes. Most engines support B-Tree indexes.
23. There are fewer and less sophisticated tools for administration.
24. There is no IDE and debugger that approaches the level of
sophistication you may be accustomed to. Youll probably be writing your
stored procedures in a text editor and debugging them by adding statements
that insert rows into a table called debug_log.
25. Each table can have a different storage backend (storage engine).
26. Each storage engine can have widely varying behavior, features, and
27. Foreign keys are not supported in most storage engines.
28. The default storage engine is non-transactional and corrupts easily.
29. Oracle owns InnoDB, the most advanced and popular storage engine.
30. Certain types of execution plans are only supported in some storage
engines. Certain types of COUNT() queries execute instantly in some storage
engines and slowly in others.
31. Execution plans are not cached globally, only per-connection.
32. Full-text search is limited and only available for non-transactional
storage backends. Ditto for GIS/spatial types and queries.
33. There are no resource controls. A completely unprivileged user can
effortlessly run the server out of memory and crash it, or use up all CPU
34. There are no integrated or add-on business intelligence, OLAP cube,
35. There is nothing analogous to Grid Control.
36. There is nothing even remotely like RAC. If you are asking How do I
build RAC with MySQL, you are asking the wrong question.
37. There are no user-defined types or domains.
38. The number of joins per query is limited to 61.
39. MySQL supports a smaller subset of SQL syntax. There are no recursive
queries, common table expressions, or windowing functions. There are a few
extensions to SQL that are somewhat analogous to MERGE and similar features,
but are very simplistic in comparison.
40. There are no functional columns (e.g. a column whose value is
calculated as an expression).
41. You cannot create an index on an expression, you can only index
42. There are no materialized views.
43. The statistics vary between storage engines and regardless of the
storage engine, are limited to simple cardinality and rows-in-a-range. In
other words, statistics on data distribution are limited. There is not much
control over updating of statistics.
44. There is no built-in promotion or failover mechanism.
45. Replication is asynchronous and has many limitations and edge cases.
For example, it is single-threaded, so a powerful slave can find it hard to
replicate fast enough to keep up with a less powerful master.
46. Cluster is not what you think it is. Maybe I already said that, but
it bears repeating.
47. The data dictionary (INFORMATION_SCHEMA) is limited and very slow (it
can easily crash a busy server).
48. There is no online ALTER TABLE.
49. There are no sequences.
50. DDL such as ALTER TABLE or CREATE TABLE is non-transactional. It
commits open transactions and cannot be rolled back or crash-recovered.
Schema is stored in the filesystem independently of the storage engine."