bargainhasem.blogg.se - Lua table insert sorted inmemory hashmap

#LUA TABLE INSERT SORTED INMEMORY HASHMAP CODE#
#LUA TABLE INSERT SORTED INMEMORY HASHMAP PLUS#
#LUA TABLE INSERT SORTED INMEMORY HASHMAP PROFESSIONAL#

Function pairs() is iterated for all keys, but the iteration order is affected by the internal representation of table.

#LUA TABLE INSERT SORTED INMEMORY HASHMAP PLUS#

Function ipairs() is iterated as while type(t) ~= ‘nil’ - not for all keys, but, on the plus side, in a predictable way, and the order is guaranteed.

Table length operator #t is only defined for arrays without holes.

Now let’s talk about the second half of the table - the array. OK, iteration for string keys is clear, no more questions. The cost of a search does not worsen when a dead node is present on the way to collision resolution. Task O(n) to search for it needs to be performed when deleting. Generally, when the main node is deleted for the searched key, the link to the colliding element needs to be reassigned to the predecessor (if present) of this main node. Collisions are resolved by the chain method. What is strongly discouraged is to add new keys to the table within the cycle as reallocation or re-hashing may occur, and then iteration will bust.Īn additional note from Igor Munkin: the reason is lookup in general, not iteration. This is done for a reason, to make it possible to delete values and not disturb iteration order.

#LUA TABLE INSERT SORTED INMEMORY HASHMAP CODE#

Conceptually, this is what the code looks like: The most complete version of code from the publication, including all the experiments, can be found on GitHub. This internal representation will affect behaviors of some functions, which I’m going to discuss here.įor demonstration, I took LuaJIT source code and patched the tostring() method a bit so that it would print out the size and all the contents of C structure to stdout using printf(). There’s something that is more important: two tables may contain the same keys and values, but differ in terms of internal representation. Moreover, as a Lua developer, I have no need to speculate about what a table looks like on the inside. I was about to describe the logic LuaJIT is guided by when new elements are inserted, but this a rather sophisticated algorithm. Both are represented by continuous storage areas. */Ī table has two parts: array and hashmap. Uint32_t hmask /* Hash part mask (size of hash part - 1). Uint32_t asize /* Size of array part (keys ). Scientifically speaking, a table is an associative array. Values of any type can be used as keys (except for nil). A table can be used both as a data array (if the keys are integer-valued) and as a key-value repository. Tables in Lua are the only composite data type designed to suit any purpose. There is another good presentation about tables in PUC-Rio implementation, if you’re interested. Our version is a bit patched as compared to the authentic LuaJIT, but the differences don’t impact tables. In this article, I’m going to discuss mostly LuaJIT 2.1.0, which is used in Tarantool. Lua has several implementations and several versions.

#LUA TABLE INSERT SORTED INMEMORY HASHMAP PROFESSIONAL#

Lua is my primary professional programming language, and if one wants to write good code, one needs at least to peek behind the curtain. In this article, I’m going to tell you about the internals of Lua tables and special considerations for their use. Books.I don’t know about you, but I really like to get inside all sorts of systems. The following script creates a dummy database named BookStore with one table i.e. In this article, you will see what the clustered and non-clustered indexes are, what are the differences between the two types and how they can be created via SQL CREATE INDEX statement. There are two major types of indexes in SQL Server: clustered indexes and non-clustered indexes. Particularly, if you have a huge number of records in your database, indexes can speed up the query execution process. Database indexes are similar and come handy. Therefore, if you want to search for any specific topic, you simply go to the index, find the page number of the topic, and go to that specific page number.

A book index may have a list of topics discussed in a book in alphabetical order. An index in a database is very similar to an index in a book. The SQL CREATE INDEX statement is used to create clustered as well as non-clustered indexes in SQL Server.