consistency

问题 My program (only 1 process and 1 thread) sequentially write n consecutive chunks of data to a file on a HDD (regular kind of HDD) using plain old write system call. It's like some kind of append-only log file. After a system crash (power failure, not HDD failure), I read back and verified that chunks[i] (0 < i < n) had been entirely written down to disk (by checking length). May be the content of the chunk is not checksum correct but still the whole chunks[i] stably sit on the surface of the

问题 For the sake of question, let's say i have 2 microservices. Identity management Accounting I know that each microservice should not be tightly coupled and it should have it's own database. Let's say that accounting has invoices and each invoice has issuing agent. Agent from accounting also exists as User in Identity microservice. If i understood well, data from identity management (users), should be copied to accounting (agents), and should copy only data which are needed for that bounded

问题 This question is a refinement of my question Different ways of observing data changes. I still have a lot of classes in my C++ application, which are updated (or could be updated) frequently in complex mathematical routines and in complex pieces of business logic. If I go for the 'observer' approach, and send out notifications every time a value of an instance is changed, I have 2 big risks: sending out the notifications itself may slow down the applications seriously if user interface

问题 I am looking for a good, up to date and "decision helping" explanation on how to choose a NoSQL database engine for storing all the events in a CQRS designed application. I am currently a newcomer to all things around NoSQL (but learning): please be clear and do not hesitate to explain your point of view in an (almost too much) precise manner. This post may deserve other newcomers like me. This database will: Be able to insert 2 to 10 rows per updates asked by the front view (in my case,

问题 I have taken a database class this semester and we are studying about maintaining cache consistency between the RDBMS and a cache server such as memcached. The consistency issues arise when there are race conditions. For example: Suppose I do a get(key) from the cache and there is a cache miss. Because I get a cache miss, I fetch the data from the database, and then do a put(key,value) into the cache. But, a race condition might happen, where some other user might delete the data I fetched

问题 In Python, find and index are very similar methods, used to look up values in a sequence type. find is used for strings, while index is for lists and tuples. They both return the lowest index (the index furthest to the left) that the supplied argument is found. For example, both of the following would return 1 : "abc".find("b") [1,2,3].index(2) However, one thing I'm somewhat confused about is that, even though the two methods are very similar, and fill nearly the same role, just for

问题 It seems that the company that I work for is always struggling with our customers’ server environments . Specifically, we almost always encounter problems with testing servers and production servers, and the fact that they always seem to be configured differently. When we test the applications that we develop, the testing servers behave in one way, and thus we tweak and configure our applications to fit that particular behavior. But when we install the same application on the production

问题 Recently I am building a REST api as part of an assignment where I am suppose to increment a counter in the database table, assuming the table has only one column, I am suppose to fire like 1000 requests per second to this REST api to increment the counter and at the end the data should be consistent i.e. if initially the counter value in DB is 0 then after the succesful run of 1000 requests concurrently it should be 1000. No worries so far I achieved it via database row-level locking, other

问题 This is a follow-up question from this that considered evalc , instead of figgling with file-descriptors manually. You can see below an example about poor sanitization. I want to remove things such as trailing characters, all whitespaces, all newlines etc -- that usually cause unexpected things -- is there a ready sanitization command to do this? EDU>> a a = 1 +1*{x} -1*{y}*{z} EDU>> b b = 1 +1*{x} -1*{y}*{z} EDU>> isequal(a,b) ans = 0 回答1: I don't know whether there exist any ready robust

问题 My understanding is that Memcached is lockless (in its default configuration), such that no client can impede any other client's operation. If that is the case, then how does Memcached handle two or more clients attempting to update the same object at the same time? How does Memcached handle multiple versions of an object? Simply take the one whose update finished last and evict the other versions from the cache? Is the database actively invalidating objects cached on a Memcached server? 回答1: