I understand GORM offers support to wrap commands in transactions, for recovery in case of failures. But it's unclear to me (from the docs) if GORM transactions support some form of row locking or table locking. If so, I would love to know how that works
I have gone through the docs and read through a couple of questions on stack overflow but haven't found anything
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I am getting confused about PostgreSQL. In some places people are saying it's NoSQL, and in some places people are saying it's not NoSQL. I have seen something Postgres Plus which is actual NoSQL.
Can you tell me what is true?
You have been confused my marketing and buzzwords.
“NoSQL” is a buzzword describing a diverse collection of database systems that focus on “semi-structured” data (that do not fit well into a tabular representation), sharding and high concurrency at the expense of transactional integrity and consistency, the latter being among the basic tenets of relational database management systems (RDBMS).
Since SQL is the language normally used to interact with an RDBMS, the term “NoSQL” is used as a name for all these systems. Perhaps the name was also chosen because SQL, being verbose and often hard to understand, evokes negative reactions in many programmers.
Now PostgreSQL, like many other RDBMS, has added support for JSON data, which is the most popular format for semi-structured data commonly stored in NoSQL systems. Now you can say that PostgreSQL supports a certain feature commonly found in NoSQL databases.
Still, SQL is the only way to interact with a PostgreSQL database, so you couldn't call it a NoSQL database and keep a straight face unless you were in marketing.
Postgres Plus is a closed source fork of PostgreSQL, so the same applies to it.
PostgreSQL is not NoSQL.
PostgreSQL is a classical, relational database server (and syntax) supporting most of the SQL standards.
On a sidenote, I suggest doing some research into the differences and advantages. They both have a solid place and time.
PostgreSQL prides itself in standards compliance. Its SQL implementation strongly conforms to the ANSI-SQL:2008 standard. It has full support for subqueries (including subselects in the FROM clause), read-committed and serializable transaction isolation levels. And while PostgreSQL has a fully relational system catalog which itself supports multiple schemas per database, its catalog is also accessible through the Information Schema as defined in the SQL standard.
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Module pg-promise provides method sequence to execute infinite sequences, suitable for massive transactions, like bulk inserts, with way over 1,000 records. And it supports query streams for high-performance, read-only queries.
Does Sequelize offer anything similar to those things?
Sorry for asking such basic things, but I am new and don't have any idea about these two.
Thanks for your response and suggestions.
This answer will probably anger some of the Sequelize fans, but in the name of truth...
What you're referring to within pg-promise is fully documented in Data Imports.
And no, Sequelize doesn't have anything like that.
And in addition, Sequelize is known to be plagued by performance issues, like this one: Transactions extremely slow when inserting 1000s of records, ones that are very bad and very old at the same time.
I am using Entity Framework, and I have tracked SQL Server using SQL Server Profiler. And I found that when I query the database using EF, the SQL Profiler will show the following:
set transaction isolation level read committed.
So what does this mean?
You should check the wiki about isolation levels. I guess you know transactions a little bit, the SaveContext() saves the changes in a transaction. There are several transaction levels, with increasing error filtering capabilities and decreasing performance. It is a good task to find the balance between safety and performance.
The read committed transaction level protects you from "dirty reads", but doesn't protect from "non-repeatable reads" and "phantom reads" (see wiki). Kinda deep topic, but you shall go through it once you plan to create more complicated and safe systems.
You can modify the transaction level like it is written here. But for basic applications you won't need this.
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Please help me to setup connectivity from PostgreSQL to Informix (latest versions for both). I would like to be able to perform a query on Informix from PostgreSQL. I am looking for a solution that will not require data exports (from Informix) and imports (to PostgreSQL) for every query.
I am very new in PostgreSQL and need detailed instructions.
As Chris Travers said, what you're seeking to do is not easy to do.
In theory, if you were working with Informix and needed to access PostgreSQL, you could (buy and) use the Enterprise Gateway Manager (EGM) and use the ODBC driver for PostgreSQL to allow Informix to connect to PostgreSQL. The EGM would do its utmost to appear to be another Informix database while actually accessing PostgreSQL. (I've not validated that PostgreSQL is supported, but EGM basically needs an ODBC driver to work, so there shouldn't be any problem — 'famous last words', probably.) This will include an emulation of 2PC (two-phase commit); not perfect, but moderately close.
For the converse connection (working with PostgreSQL and connecting to Informix), you will need to look to the PostgreSQL tool suite — or other sources.
You haven't said which version you are using. There are some limitations to be aware of but there are a wide range of choices.
Since you say this is import/export, I will assume that read-only options are not sufficient. That rules out PostgreSQL 9.1's foreign data wrapper system.
Depending on your version David Fetter's DBI-Link may suit your needs since it can execute queries on remote tables (see https://github.com/davidfetter/DBI-Link). It hasn't been updated in a while but the implementation should be pretty stable and usable across versions. If that fails you can write stored procedures in an untrusted language (PL/PythonU, PL/PerlU, etc) to connect to Informix and run the queries there. Note there are limits regarding transaction handling you will run into in this case so you may want to run any queries on the other tables using deferred constraint triggers so everything gets run at commit time.
Edit: A cleaner way occurred to me: use foreign data wrappers for import and a separate client app for export.
In this approach, you are going to have four basic components but this will be loosely coupled and subject to proper transactional controls. You can even use two-phase commit if you want. The four components are (not providing a complete working example here but at least a roadmap to one):
Foreign data wrappers for data import, allowing you to see data from Informix.
Views of data to be exported.
External application which manages the export aspect, written in a language of your choice. This listens on a channel like LISTEN export_informix;
Triggers on underlying tables which make view of data to be exported which raise a NOTIFY export_informix
The notifications are riased on the commit and so basically you have two stages to your transaction in this way:
Write data in PostgreSQL, flag data to be exported. Commit.
Read data from PostgreSQL, export to Informix. Commit on both sides (TPC?).
I have recently started getting familiarized with NoSQL (HBase). I am definitely a noob.
I was investigating about ORMs and high level clients which can be used on HBase and came across a few.
Some ORM libraries like Kundera are providing SQL like data query functionality. I am finding this a little counter intuitive.
Can any one help me understand why we would again need SQL like querying if the whole objective was to move away from it?
Also can anyone comment on your experiences with ORMs for HBase? I looked at a few of them from http://wiki.apache.org/hadoop/SupportingProjects and started looking at Kundera.
Another related question - Does data query with Kundera run map reduce jobs internally?
kundera or Spring data might provide user friendly ORM layer over NoSQL databases, but the underlying entity model still has to be NoSQL friendly. This means that NoSQL users should not blindly follow RDBMS modeling strategies but design ORM entities in such a way so that all NoSQL capabilities can be used.
As a thumb rule, the kundera ORM entities should be designed using query-first strategy where first the queries need to defined so as to create primary keys and also ensuring that relationship model is used as minimal as possible. Querying on random columns and full scans should be avoided and so data might have to be replicated across entities for reducing multiple entity look ups. Also, transactions management needs to be planned. FYI, kundera does not support transactions(beyond single row TX supported by Hbase/Cassandra).
Reason for using Kundera:
1) If looking for SQL like support over HBase. As it is build on top of HBase native API, so it simply transforms these SQL queries in to corresponding GET or PUT method calls.
2) Currently it support HBase-0.20.6 only. Kundera-2.0.6 will enable support for HBase 0-90.x versions.
3) Kundera does not do sometihng out of the box to provide map reduce over SQL like queries. However support for such thing will be provided in Kundera-2.0.6 by enabling support for Hive native queries only!
It is totally JPA compliant, so no need to learn something new. It simply hides complexity at developer level with very minimal effort.
SQL like querying is for developement ease, quick developement, less error prone and reusability ofcourse!
-Vivek