Overview In application level, ”PostgreSQL“ has native supports for using SSL connections. This requires that OpenSSL is installed on both client and server systems and that support in PostgreSQL is enabled at build time. With SSL, we can: Encrypted data on Internet transmission Allow client to authorize the server(PostgreSQL), which can protect the client from connecting to the attacker’s server Allow server to authorize the client, which can stop the attacker from connecting to the database even if password leak. Just encrypt internet transmission build binary from source just configure with -with-openssl option. You may need to install ssl-dev tools first ...

sequence type background From official documents: 9.17. Sequence Manipulation Functions CREATE SEQUENCE Sequence objects are special single-row tables created with CREATE SEQUENCE. Sequence objects are commonly used to generate unique identifiers for rows of a table. The sequence functions, provide simple, multiuser-safe methods for obtaining successive sequence values from sequence objects. Main function There is no much concerns about these functions nextval Advances the sequence object to its next value and returns that value setval ...

Abstract a protocol for schema evolution in a globally distributed database management system with shared data, stateless servers, and no global membership. asynchronous all servers can access and update all data during a schema change INTRODUCTION Schema evolution: the ability to change a database’s definition without the loss of data F1 is built on top of Spanner, a globally distributed KV data store Main feature The main features of F1 that impact schema changes are: ...

Primitive Operation if Transactions There are three address spaces that transaction interact in important ways: The space of disk blocks holding the database elements. The memory address space managed by buffer manager. The local address space of the transaction. To describe a transaction, we need some operation notions:(X below is a database element while t is a local varible, and we suppose a database element is no larger than a single block) ...

Definiteness： Suppose Alice has number $i$ and Bob has number $j$ and $1\leq i,j \leq 9$. We need a protocol for them to decide whether $i < j$ in the end(aside from their own values) Solution: Let $M$ be the set of all $N$-bit nonnegative integers Let $Q_N$ be the set of all one-one and onto function from $M$ to $M$ Alice generates a public key from $Q_N$, called $E_a$, and the inverse function of $E_a$ is $D_a$ Bob picks a random value $x \in M$, compute $k = E_a(x)$, then send $k - j$ to Alice Alice computes $y_u=D_a(k - j + u)$ for $u = 1,2,\dots,9$ Alice generates a random prime $p$ of $N/2$-bit, and computes $z_u=y_u(\mod p)$ for all $u$. Alice repeats step 4 until all $z_u$ differ by at least 2 in the $\mod p$ sense Alice sends the $p$ and $z_1,z_2,\dots,z_i,z_{i+1}+1,\dots,z_{9} +1$ (all in $\mod p$ sense)to Bob Bob looks at the $j$-th value(not counting p) sent from Alice, and decides that $i\geq j$ if it is equal to $x \mod p$, or $i<j$ otherwise

The functions described in this chapter are often referred to as unbuffered I/O(which each read or write invokes a system call in the kernel), in contrast to the standard I/O routines File Descriptors To the kernel, all open files are referred to by file descriptors. A file descriptor is a non-negative integer. When we open an existing file or create a new file, the kernel returns a file descriptor to the process. When we want to read or write a file, we identify the file with the file descriptor that was returned by open or creat as an argument to either read or write. By convention, UNIX System shells associate file descriptor 0 with the standard input of a process, file descriptor 1 with the standard output, and file descriptor 2 with the standard error File descriptors range from 0 through OPEN_MAX−1 open and openat code #include <fcntl.h> int open(const char *path, int oflag, ... /* mode_t mode */ ); int openat(int fd, const char *path, int oflag, ... /* mode_t mode */ ); //Both return: file descriptor if OK, −1 on error This function has a multitude of options, which are specified by the oflag argument. This argument is formed by ORing together one or more of the following constants from the<fcntl.h> header ...

Overview This chapter explains the content of clog clog(commit log), records the commit status of each transaction. The log exists both in memory mannaged by slru buffer and disk for durability. The commit status can be the four kinds below: #define TRANSACTION_STATUS_IN_PROGRESS 0x00 #define TRANSACTION_STATUS_COMMITTED 0x01 #define TRANSACTION_STATUS_ABORTED 0x02 #define TRANSACTION_STATUS_SUB_COMMITTED 0x03 In-Disk Representation Thinking that the commit status of each transaction composites an array clog[] and clog[xid] records the status, we can easily store the array to disk by the slru. ...

concept cublasDgemm is a convenient function in cublas to compute the product of two matrix, while letter ‘D’ in cublasDgemm means double. Before reading this post, basic cuda functions like cudaMalloc are what you are supposed to know. basic use Definition of this function cublasStatus_t cublasDgemm(cublasHandle_t handle, cublasOperation_t transa, cublasOperation_t transb, int m, int n, int k, const double *alpha, const double *A, int lda, const double *B, int ldb, const double *beta, double *C, int ldc) Basic information of parameters is show in this page. Simply put, $C = \alpha A \times B + \beta C $ .But it may remains confused for fresher. Below is an simple example. ...

high level view See Queries in PostgreSQL: 6. Hashing One-pass hash join Note that join in PostgreSql, we scan the right relation first, which means that the right relation is the “inner relation” and the left relation is the outer one. Two-pass hash join Since we can’t allocate as much memory as we want, instead of building a hash table of the entire table, PG split the tables to several batches where all tuples have the same hash value flag. ...

principle pg_repack 1.5.0 – Reorganize tables in PostgreSQL databases with minimal locks https://github.com/reorg/pg_repack create a log table to record changes made to the original table add a trigger onto the original table, logging INSERTs, UPDATEs and DELETEs into our log table create a new table containing all the rows in the old table build indexes on this new table apply all changes which have accrued in the log table to the new table swap the tables, including indexes and toast tables, using the system catalogs drop the original table The basic idea is ...