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New backend dirs html file.
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‎src/tools/BACKEND_DIRS.html

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<HTML>
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<HEAD>
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<TITLE>PostgreSQL Backend Directories</TITLE>
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</HEAD>
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<BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
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<H1 ALIGN=CENTER>
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PostgreSQL Backend Directories
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</H1>
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<H2 ALIGN=CENTER>
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by Bruce Momjian
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</H2 ALIGN=CENTER>
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<H2>
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<A HREF="../backend//bootstrap">bootstrap</A> - creates initial template database via initdb
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</H2>
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<P>
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Because PostgreSQL requires access to system tables for almost every
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operation, getting those system tables in place is a problem.
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You can't just create the tables and insert data into them in the normal way,
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because table creation and insertion requires the tables to already
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exist.
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This code <I>jams</I> the data directly into tables using a
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special syntax used only by the bootstrap procedure.
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</P>
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<H2>
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<A HREF="../backend//main">main</A> - passes control to postmaster or postgres
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</H2>
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<P>
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This checks the process name(argv[0]) and various flags, and passes
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control to the postmaster or postgres backend code.
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</P>
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<H2>
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<A HREF="../backend//postmaster">postmaster</A> - controls postgres server startup/termination
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</H2>
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<P>
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This creates shared memory, and then goes into a loop waiting for
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connection requests.
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When a connection request arrives, a <I>postgres</I> backend is started,
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and the connection is passed to it.
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</P>
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<H2>
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<A HREF="../backend//libpq">libpq</A> - backend libpq library routines
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</H2>
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<P>
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This handles communication to the client processes.
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</P>
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<H2>
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<A HREF="../backend//tcop">tcop</A> - traffic cop, dispatches request to proper module
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</H2>
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<P>
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This contains the <I>postgres</I> backend main handler, as well as the
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code that makes calls to the parser, optimizer, executor, and
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<I>/commands</I> functions.
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</P>
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<H2>
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<A HREF="../backend//parser">parser</A> - converts SQL query to query tree
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</H2>
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<P>
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This converts SQL queries coming from <I>libpq</I> into command-specific
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structures to be used the the optimizer/executor, or <I>/commands</I>
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routines.
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The SQL is lexically analyzed into keywords, identifiers, and constants,
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and passed to the parser.
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The parser creates command-specific structures to hold the elements of
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the query.
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The command-specific structures are then broken apart, checked, and passed to
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<I>/commands</I> processing routines, or converted into <I>Lists</I> of
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<I>Nodes</I> to be handled by the optimizer and executor.
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</P>
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<H2>
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<A HREF="../backend//optimizer">optimizer</A> - creates path and plan
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</H2>
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<P>
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This uses the parser output to generate an optimal plan for the
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executor.
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</P>
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<H4>
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<A HREF="../backend//optimizer/path">optimizer/path</A> - creates path from parser output
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</H4>
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<P>
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This takes the parser query output, and generates all possible methods of
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executing the request.
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It examines table join order, <I>where</I> clause restrictions,
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and optimizer table statistics to evaluate each possible execution
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method, and assigns a cost to each.
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</P>
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<H4>
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<A HREF="../backend//optimizer/geqo">optimizer/geqo</A> - genetic query optimizer
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</H4>
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<P>
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<I>optimizer/path</I> evaluates all possible ways to join the requested tables.
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When the number of tables becomes great, the number of tests made
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becomes great too.
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The Genetic Query Optimizer considers each table separately, then figures
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the most optimal order to perform the join.
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For a few tables, this method takes longer, but for a large number of
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tables, it is faster.
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There is an option to control when this feature is used.
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</P>
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<H4>
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<A HREF="../backend//optimizer/plan">optimizer/plan</A> - optimizes path output
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</H4>
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<P>
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This takes the <I>optimizer/path</I> output, chooses the path with the
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least cost, and creates a plan for the executor.
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</P>
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<H4>
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<A HREF="../backend//optimizer/prep">optimizer/prep</A> - handle special plan cases
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</H4>
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<P>
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This does special plan processing.
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</P>
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<H4>
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<A HREF="../backend//optimizer/util">optimizer/util</A> - optimizer support routines
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</H4>
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<P>
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This contains support routines used by other parts of the optimizer.
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</P>
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<H2>
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<A HREF="../backend//executor">executor</A> - executes complex node plans from optimizer
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</H2>
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<P>
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This handles <I>select, insert, update,</I> and <I>delete</I> statements.
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The operations required to handle these statement types include
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heap scans, index scans, sorting, joining tables, grouping, aggregates,
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and uniqueness.
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</P>
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<H2>
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<A HREF="../backend//commands">commands</A> - commands that do not require the executor
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</H2>
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<P>
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These process SQL commands that do not require complex handling.
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It includes <I>vacuum, copy, alter, create table, create type,</I> and
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many others.
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The code is called with the structures generated by the parser.
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Most of the routines do some processing, then call lower-level functions
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in the catalog directory to do the actual work.
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</P>
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<H2>
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<A HREF="../backend//catalog">catalog</A> - system catalog manipulation
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</H2>
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<P>
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This contains functions that manipulate the system tables or catalogs.
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Table, index, procedure, operator, type, and aggregate creation and
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manipulation routines are here.
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These are low-level routines, and are usually called by upper routines
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that pre-format user requests into a predefined format.
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</P>
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<H2>
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<A HREF="../backend//storage">storage</A> - manages various storage systems
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</H2>
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<P>
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These allow uniform resource access by the backend.
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<BR>
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<BR>
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<A HREF="../backend//storage/buffer">storage/buffer</A> - shared buffer pool manager
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<BR>
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<A HREF="../backend//storage/file">storage/file</A> - file manager
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<BR>
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<A HREF="../backend//storage/ipc">storage/ipc</A> - semaphores and shared memory
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<BR>
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<A HREF="../backend//storage/large_object">storage/large_object</A> - large objects
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<BR>
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<A HREF="../backend//storage/lmgr">storage/lmgr</A> - lock manager
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<BR>
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<A HREF="../backend//storage/page">storage/page</A> - page manager
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<BR>
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<A HREF="../backend//storage/smgr">storage/smgr</A> - storage/disk manager
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<BR>
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<BR>
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</P>
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<H2>
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<A HREF="../backend//access">access</A> - various data access methods
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</H2>
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<P>
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These control the way data is accessed in heap, indexes, and
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transactions.
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<BR>
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<BR>
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<A HREF="../backend//access/common">access/common</A> - common access routines
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<BR>
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<A HREF="../backend//access/gist">access/gist</A> - easy-to-define access method system
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<BR>
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<A HREF="../backend//access/hash">access/hash</A> - hash
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<BR>
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<A HREF="../backend//access/heap">access/heap</A> - heap is use to store data rows
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<BR>
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<A HREF="../backend//access/index">access/index</A> - used by all index types
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<BR>
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<A HREF="../backend//access/nbtree">access/nbtree</A> - Lehman and Yao's btree management algorithm
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<BR>
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<A HREF="../backend//access/rtree">access/rtree</A> - used for indexing of 2-dimensional data
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<BR>
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<A HREF="../backend//access/transam">access/transam</A> - transaction manager (BEGIN/ABORT/COMMIT)
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<BR>
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<BR>
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</P>
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<H2>
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<A HREF="../backend//nodes">nodes</A> - creation/manipulation of nodes and lists
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</H2>
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<P>
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PostgreSQL stores information about SQL queries in structures called
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nodes.
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<I>Nodes</I> are generic containers that have a <I>type</I> field and then a
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type-specific data section.
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Nodes are usually placed in <I>Lists.</I>
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A <I>List</I> is container with an <I>elem</I> element,
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and a <I>next</I> field that points to the next <I>List.</I>
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These <I>List</I> structures are chained together in a forward linked list.
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In this way, a chain of <I>List</I>s can contain an unlimited number of <I>Node</I>
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elements, and each <I>Node</I> can contain any data type.
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These are used extensively in the parser, optimizer, and executor to
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store requests and data.
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</P>
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<H2>
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<A HREF="../backend//utils">utils</A> - support routines
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</H2>
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<H4>
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<A HREF="../backend//utils/adt">utils/adt</A> - built-in data type routines
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</H4>
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<P>
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This contains all the PostgreSQL builtin data types.
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</P>
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<H4>
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<A HREF="../backend//utils/cache">utils/cache</A> - system/relation/function cache routines
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</H4>
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<P>
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PostgreSQL supports arbitrary data types, so no data types are hard-coded
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into the core backend routines.
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When the backend needs to find out about a type, is does a lookup of a
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system table.
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Because these system tables are referred to often, a cache is maintained
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that speeds lookups.
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There is a system relation cache, a function/operator cache, and a relation
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information cache.
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This last cache maintains information about all recently-accessed
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tables, not just system ones.
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</P>
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<H4>
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<A HREF="../backend//utils/error">utils/error</A> - error reporting routines
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</H4>
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<P>
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Reports backend errors to the front end.
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</P>
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<H4>
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<A HREF="../backend//utils/fmgr">utils/fmgr</A> - function manager
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</H4>
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<P>
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This handles the calling of dynamically-loaded functions, and the calling
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of functions defined in the system tables.
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</P>
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<H4>
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<A HREF="../backend//utils/hash">utils/hash</A> - hash routines for internal algorithms
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</H4>
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<P>
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These hash routines are used by the cache and memory-manager routines to
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do quick lookups of dynamic data storage structures maintained by the
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backend.
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</P>
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<H4>
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<A HREF="../backend//utils/init">utils/init</A> - various initialization stuff
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</H4>
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<H4>
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<A HREF="../backend//utils/misc">utils/misc</A> - miscellaneous stuff
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</H4>
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<H4>
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<A HREF="../backend//utils/mmgr">utils/mmgr</A> - memory manager(process-local memory)
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</H4>
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<P>
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When PostgreSQL allocates memory, it does so in an explicit context.
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Contexts can be statement-specific, transaction-specific, or
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persistent/global.
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By doing this, the backend can easily free memory once a statement or
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transaction completes.
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</P>
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<H4>
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<A HREF="../backend//utils/sort">utils/sort</A> - sort routines for internal algorithms
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</H4>
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<P>
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When statement output must be sorted as part of a backend operation,
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this code sorts the tuples, either in memory or using disk files.
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</P>
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<H4>
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<A HREF="../backend//utils/time">utils/time</A> - transaction time qualification routines
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</H4>
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<P>
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These routines do checking of tuple internal columns to determine if the
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current row is still valid, or is part of a non-committed transaction or
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superseded by a new row.
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</P>
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<H2>
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<A HREF="../backend//include">include</A> - include files
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</H2>
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<P>
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There are include directories for each subsystem.
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</P>
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<H2>
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<A HREF="../backend//lib">lib</A> - support library
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</H2>
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<P>
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This houses several generic routines.
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</P>
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<H2>
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<A HREF="../backend//regex">regex</A> - regular expression library
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</H2>
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<P>
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This is used for regular expression handling in the backend, i.e. '~'.
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</P>
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<H2>
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<A HREF="../backend//rewrite">rewrite</A> - rules system
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</H2>
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<P>
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This does processing for the rules system.
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</P>
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<H2>
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<A HREF="../backend//tioga">tioga</A> - unused (array handling?)
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</H2>
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<HR>
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<ADDRESS>
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Maintainer: Bruce Momjian<A
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HREF="mailto:maillist@candle.pha.pa.us">maillist@candle.pha.pa.us</a>)<BR>
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Last updated: Mon Oct 27 11:01:08 EST 1997
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</ADDRESS>

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