SQL/MX 2.x Reference Manual (G06.24+, H06.03+)

HP NonStop SQL/MX Reference Manual—523725-004
C-1
C Limits
This appendix lists limits for various parts of NonStop SQL/MX:
•
Constraints
°
The maximum combined length of the columns for a REFERENCE, PRIMARY
KEY, or UNIQUE constraint is 255 bytes.
•
DROP SCHEMA CASCADE transaction limits
°
You might need to increase the number of locks per volume, or DROP
SCHEMA CASCADE can fail.
•
EXTENTS
°
Limited only by size of disk.
•
FROM clause of the SELECT statement
°
NonStop SQL/MX typically generates good plans up to 16 tables and tries to
generate plans with acceptable performance for queries up to 40 tables.
Beyond that limit, the queries require some tuning to compile and run.
•
IN predicate
°
1900 expressions are allowed.
•
Indexes
°
The maximum combined length of the columns for an index is 255 bytes. A
nonunique index consists of columns and a clustering key. A unique index
consists of columns only.
°
There is no restriction on the number of indexes per table but creating many
indexes on a table will affect performance.
°
There are no restrictions on the number of partitions an index supports, but
beyond 512, performance and memory issues might occur.
•
INSERT operations
°
150 records can be inserted into SQL/MX tables in a single INSERT operation.
250 records can be inserted into SQL/MP tables in a single INSERT operation.
•
Joins
°
40 tables can be joined, including base tables of views, but joining more tables
affects performance.
•
MAXEXTENTS size
°
768 (compare with 919 for NonStop SQL/MP)
•
Partitions