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algorithm nested_loop_join is for each tuple r in R do for each tuple s in S do if r and s satisfy the join condition then yield tuple <r,s> This algorithm will involve n r *b s + b r block transfers and n r +b r seeks, where b r and b s are number of blocks in relations R and S respectively, and n r is the number of tuples in relation R.
This prevents records from being overwritten incorrectly, but allows only one record to be processed at a time, locking out other users who need to edit records at the same time. To allow several users to edit a database table at the same time and also prevent inconsistencies created by unrestricted access, a single record can be locked when ...
Raynal demonstrates how to implement an R/W lock using two mutexes and a single integer counter. The counter, b, tracks the number of blocking readers. One mutex, r, protects b and is only used by readers; the other, g (for "global") ensures mutual exclusion of writers. This requires that a mutex acquired by one thread can be released by another.
lock contention: this occurs whenever one process or thread attempts to acquire a lock held by another process or thread. The more fine-grained the available locks, the less likely one process/thread will request a lock held by the other. (For example, locking a row rather than the entire table, or locking a cell rather than the entire row);
A lock can be shared (other processes can read the file/directory, but can't modify or delete it), or exclusive so that only the process which successfully acquires the lock can access or modify the object. The lock is on the whole object and not part of it. The lock must be released with the UnLock function: unlike in Unix, the operating ...
Schematic representation of how threads work under GIL. Green - thread holding GIL, red - blocked threads. A global interpreter lock (GIL) is a mechanism used in computer-language interpreters to synchronize the execution of threads so that only one native thread (per process) can execute basic operations (such as memory allocation and reference counting) at a time. [1]
In case another thread has the same number, the thread with the smallest i will enter the critical section first. In pseudocode this comparison between threads a and b can be written in the form: // Let n a - the customer number for thread a, and // i a - the thread number for thread a, then (n a, i a) < (n b, i b) which is equivalent to:
In the C programming language the line number of a source code line is one greater than the number of new-line characters read or introduced up to that point. [1] Programmers could also assign line numbers to statements in older programming languages, such as Fortran, JOSS, and BASIC. In Fortran, not every statement needed a line number, and ...