There is only one way to know: Time it. In general, I think a single join enables the database to do a lot of optimizations, as it can see all the tables it needs to scan, overhead is reduced, and it can build up the result set locally. Recently, I had about 100 select-statements which … Read more
You can use F() objects for this. Here is how you import F: from django.db.models import F New in Django 1.1. Calls to update can also use F() objects to update one field based on the value of another field in the model. This is especially useful for incrementing counters based upon their current value. … Read more
The only practical difference between the anonymous classes and the top-level classes is that the anonymous classes will hold an implicit reference to the outer class. This won’t manifest itself in performance, but will impact you if you ever serialise these classes.
(Some of this is x86 and Intel-specific. Most of the key points apply to any CPU that does hardware page walks. I also discuss ISAs like MIPS that handle TLB misses with software.) Modern x86 microarchitectures have dedicated page-walk hardware. They can even speculatively do page-walks to load TLB entries before a TLB miss actually … Read more
As alluded to in the comments by btilly and Amadan, this is due to how the Timsort sorting algorithm works. Detailed description of the algorithm is here. Timsort speeds up operation on partially sorted arrays by identifying runs of sorted elements. A run is either “ascending”, which means non-decreasing: a0 <= a1 <= a2 <= … Read more
You can’t set max heap size in .Net unless you host the CLR yourself in a process. Edit: To control the memory allocations of CLR including the max heap size, you need to use the hosting api to host the clr and specifically use the “Memory manager interfaces”, some starter info can be found here … Read more
If the query planner makes bad decisions it’s mostly one of two things: 1. The statistics are inaccurate. Do you run ANALYZE enough? Also popular in its combined form VACUUM ANALYZE. If autovacuum is on (which is the default in modern-day Postgres), ANALYZE is run automatically. But consider: Are regular VACUUM ANALYZE still recommended under … Read more
Interesting question. So, what’s going to happened ? Well if you debug with gdb you’ll see something like 3 member variables (names are not accurate): _M_begin: pointer to the first element of the dynamic array _M_end: pointer one past the last element of the dynamic array _M_capacity: pointer one past the last element that could … Read more