uuid

I would like to know how or how much can affect the performance of the server when I use UUID for my primary keys in MySQL. I suppose you are using InnoDB (You should anyway....) So read the following chapter from High performance MySQL 2ed, p.117: http://books.google.com.hk/books?id=BL0NNoFPuAQC&lpg=PA117&ots=COPMBsvA7V&dq=uuid%20innodb%20clustered%20index%20high%20performance%20mysql&pg=PA117#v=onepage&q&f=false In general, UUID is a poor choice from the performance standpoint (due to clustered index) and they have a benchmark to prove this. UUID is 36 chars long, which means 36 bytes. INT

Is there any specific reason for MongoDB generating uuid as unique identifier instead of incremental values as unique identifier?. Incrementing values or sequences require a central point of reference which is a limiting factor for scaling. ObjectIDs are designed to be reasonably unique IDs that can be independently generated in a distributed environment with monotonically increasing values (a leading timestamp component) for approximate ordering. ObjectIDs are typically generated by MongoDB drivers so there is no need to make a server round-trip to find the next available _id or wait for the

I have the table with some columns: --table create table testz ( ID uuid, name text ); Note : I want to insert ID values by passing as a parameter to the function. Because I am generating the ID value in the front end by using uuid_generate_v4() . So I need to pass the generated value to the function to insert into the table My bad try: --function CREATE OR REPLACE FUNCTION testz ( p_id varchar(50), p_name text ) RETURNS VOID AS $BODY$ BEGIN INSERT INTO testz values(p_id,p_name); END; $BODY$ LANGUAGE PLPGSQL; --EXECUTE FUNCTION SELECT testz('24f9aa53-e15c-4813-8ec3-ede1495e05f1','Abc');

1.GTID的概念 GTID（global transaction identifier）是全局事务标识符，在MySQL5.6版本中作为一个超级特性被推出。事务标识不仅对于Master(起源)的服务器来说是惟一的，而且在整个复制拓扑架构来说，也是全局唯一的。 1)GTID的格式 GTID = source_id:transaction_id 其中 source_id ：通过使用MySQL服务的server_uuid来表示 ， transaction_id ：是在事务提交的时候系统顺序分配的一个序列号 2)mysql.gtid_executed表 GTIDs都存储在gtid_executed数据表中，在mysql系统数据库中。每一行的数据代表一个GTID或者一个GTID集合。包括source_uuid，集合开始的事务id和集合结束的事务id 表结构如下: CREATE TABLE gtid_executed ( source_uuid CHAR(36) NOT NULL, interval_start BIGINT(20) NOT NULL, interval_end BIGINT(20) NOT NULL, PRIMARY KEY (source_uuid, interval_start) ) 备注：事务并不是立马写进gtid_executed表。当启用二进制日志的时候(log

java调用opencv进行人脸裁剪，发现上传8m左右的人脸图片，每进行一次人脸图片裁剪大约消耗5-6g的内存，导致程序很容易崩溃。以下是优化后的代码。 并且在启动的时候指定内存 nohup java -XX:MetaspaceSize=256m -XX:MaxMetaspaceSize=256m -Xms8192m -Xmx8192m -Xmn3072m -jar /dit/management-client.jar > /dit/management.log & package com.ahies.dit.management.service; import cn.hutool.core.img.ImgUtil; import cn.hutool.log.LogFactory; import com.ahies.dit.management.model.File; import com.google.common.collect.Maps; import lombok.NonNull; import net.coobird.thumbnailator.Thumbnails; import org.apache.commons.io.FileUtils; import org.apache.commons.io.FilenameUtils; import org.opencv

so on my search for an answer to my problem I found this post: Jest: How to globally mock node-uuid (or any other imported module) I already tried the answer but I can't seem to use it properly, as it´s giving me an undefined error. I'm new to the testing scene so please excuse any major errors: This was my first approach const mockF = jest.mock('uuid'); mockF.mockReturnValue('12345789'); But it wouldn't recognize the functions. "mockF.mockReturnValue is not a function" among others I tried. Then I tried to manually mock as the post suggested but can' seem to make it work, can you help me?

I would like to get an idea on how can we generate an unique identifier using two Strings. My requirement here is to generate an unique identifier for a particular document. For id generation, document 'name' and 'version' has to be used. And there should be a way to get back both 'name' and 'version' from the unique identifier of a particular document. Is there a way to do this using UUID in java? or what is the best way of doing this. Can we use hashing or encoding for this purpose and if so how? I don't know why you want to use 2 strings to generate a unique ID and it might not be possible

I'm porting a C program onto Android using the NDK. The program uses the uuid.h or uuid/uuid.h library depending on which is available. When I compile the program, gives the error message uuid.h: No such file or directory . I'm new to the NDK, so I'm not entirely sure what the problem is. I'm using cygwin on Windows; does the computer not have the uuid.h library or Android doesn't support it? Is there a workaround- can I include it somehow in the compiler settings? Finally, the program only uses the library like so: char *s; uuid_t uu; uuid_create(&uu, NULL); uuid_to_string(&uu, &s, 0);

I understand that this doesn't take a significant chunk off of the entropy involved, and that even if a whole nother character of the GUID was reserved (for any purpose), we still would have more than enough for every insect to have one, so I'm not worried, just curious. As this great answer shows, the Version 4 algorithm for generating GUIDs has the following format: xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx x is random 4 is constant, this represents the version number. y is one of: 8, 9, A, or B The RFC spec for UUIDs says that these bits must be set this way, but I don't see any reason given.