Re: Additional Chapter for Tutorial
On Fri, 2021-05-21 at 08:47 +0200, Jürgen Purtz wrote: > Peter changed the status to 'Returned with feedback' at the end of the > last commit fest. I'm not absolutely sure, but my understanding is that > the patch is rejected. There is a different status for that. "Returned with feedback" means: there was review, and further work by the author is needed, or we need more discussion if we want that or not or how it should be, but there hasn't been a lot of feedback from the author lately, so it seems that just moving it on to the next commitfest is not the right thing to do. You are welcome to re-submit the patch if you address the feedback. Yours, Laurenz Albe
Re: Additional Chapter for Tutorial
Hi Jürgen, What's going to happen with this work? If you intend to have it eventually committed, I think it will be necessary to make the patches smaller, and bring them into the commitfest app, so that others can follow progress. I for one, cannot see/remember/understand what has been done, or even whether you intend to continue with it. Thanks, Erik Peter changed the status to 'Returned with feedback' at the end of the last commit fest. I'm not absolutely sure, but my understanding is that the patch is rejected. -- Jürgen Purtz
Re: Additional Chapter for Tutorial
Hi Jürgen, What's going to happen with this work? If you intend to have it eventually committed, I think it will be necessary to make the patches smaller, and bring them into the commitfest app, so that others can follow progress. I for one, cannot see/remember/understand what has been done, or even whether you intend to continue with it. Thanks, Erik
Re: Additional Chapter for Tutorial
On Fri, Oct 23, 2020 at 6:58 AM Jürgen Purtz wrote: > Creating such a chapter in "VII. Internals" will increase the existing > chapter numbers 50 - 71, which may lead to some confusion. On the other > hand the content can possibly be applied to all supported PG versions at > the same time, which will lead to a consistent behavior. Extending one of > the existing chapters won't work because all of them handle their own > topic, eg.: "50. Overview of PostgreSQL Internals" (misleading title?) > focuses on the handling of SQL statements from parsing to execution. > > What are your thoughts? > v14 has already added a new chapter, installation from binaries. It was not back-patched. To my knowledge no one brought up these points - numbers changing or back-patching the new material. I don't see that this enhancement needs to be treated any differently. David J.
Re: Additional Chapter for Tutorial
On 21.10.20 22:33, David G. Johnston wrote: I've begun looking at this and have included quite a few html comments within the patch. However, the two main items that I have found so far are: One, I agree with Peter that this seems misplaced in Tutorial. I would create a new Internals Chapter and place this material there, or maybe consider a sub-chapter under "Overview of PostgreSQL Internals". If this is deemed to be of a more primary importance than the content in the Internals section I would recommend placing it in Reference. I feel it does fit there and given the general importance of that section readers will be inclined to click into it and skim over its content. I like the idea of dividing the material into two different chapters. The existing part "I. Tutorial" contains the first concrete steps: installation, creating database and database objects, using SQL basic and advanced features. Its typical audience consists of persons doing their first steps with PG. The new material is aimed at persons interested in implementation aspects of PG. Therefore, the part "VII. Internals" seems to be the natural place to integrate it, something like "Architecture and Implementation Aspects" or "Architecture and Implementation Cornerstones". Creating such a chapter in "VII. Internals" will increase the existing chapter numbers 50 - 71, which may lead to some confusion. On the other hand the content can possibly be applied to all supported PG versions at the same time, which will lead to a consistent behavior. Extending one of the existing chapters won't work because all of them handle their own topic, eg.: "50. Overview of PostgreSQL Internals" (misleading title?) focuses on the handling of SQL statements from parsing to execution. What are your thoughts? -- J. Purtz
Re: Additional Chapter for Tutorial
On 10.09.20 18:26, Peter Eisentraut wrote: On 2020-09-02 09:04, Jürgen Purtz wrote: On 01.09.20 23:30, Peter Eisentraut wrote: It is mostly advanced low-level information that is irrelevant for someone starting up, That applies only to the VACUUM chapter. VACUUM and AUTOVACUUM are controlled by a lot of parameters. Therefor the current documentation concerning the two mechanism spreads the description across different pages (20.4, 25.1, VACUUM command). Because of the structure of our documentation that's ok. But we should have a summary page somewhere - not necessarily in the tutorial. There is probably room for improvement, but the section numbers you mention are not about VACUUM, AFAICT, so I can't really comment on what you have in mind. Because of the additional chapter for the 'tutorial' on my local computer, the numbers increased for me. The regular chapter numbers are 19.4 and 24.1. Sorry for the confusion. In detail: 19.4: parameters to configure the server, especially five parameters 'vacuum_cost_xxx'. 19.10: parameters to configure autovacuum. 19.11: parameters to configure client connections, especially five parameters 'vacuum_xxx' concerning their freeze-behavior. 24.1: explains the general necessity of (auto)vacuum and their strategies. The page about the SQL command VACUUM explains the different options (FULL, FREEZE, ..) and their meaning. -- Jürgen Purtz
Re: Additional Chapter for Tutorial
On 2020-09-02 09:04, Jürgen Purtz wrote: On 01.09.20 23:30, Peter Eisentraut wrote: It is mostly advanced low-level information that is irrelevant for someone starting up, That applies only to the VACUUM chapter. VACUUM and AUTOVACUUM are controlled by a lot of parameters. Therefor the current documentation concerning the two mechanism spreads the description across different pages (20.4, 25.1, VACUUM command). Because of the structure of our documentation that's ok. But we should have a summary page somewhere - not necessarily in the tutorial. There is probably room for improvement, but the section numbers you mention are not about VACUUM, AFAICT, so I can't really comment on what you have in mind. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: Additional Chapter for Tutorial
On 01.09.20 23:30, Peter Eisentraut wrote: It is mostly advanced low-level information that is irrelevant for someone starting up, That applies only to the VACUUM chapter. VACUUM and AUTOVACUUM are controlled by a lot of parameters. Therefor the current documentation concerning the two mechanism spreads the description across different pages (20.4, 25.1, VACUUM command). Because of the structure of our documentation that's ok. But we should have a summary page somewhere - not necessarily in the tutorial. the most part the information just duplicates what is already explained elsewhere. That is the nature of a tutorial respectively a summary. -- J. Purtz
Re: Additional Chapter for Tutorial
Again, I don't see how this belongs into the tutorial. It is mostly advanced low-level information that is irrelevant for someone starting up, it is not hands-on, so quite unlike the rest of the tutorial, and for the most part the information just duplicates what is already explained elsewhere. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
RE: Additional Chapter for Tutorial
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Re: Additional Chapter for Tutorial
On 2020-07-17 11:32, Jürgen Purtz wrote: On 12.07.20 22:45, Daniel Gustafsson wrote: This patch no longer applies, due to conflicts in start.sgml, can you please submit a rebased version? cheers ./daniel New version attached. [0005-architecture.patch] Hi, I went through the architecture.sgml file once, and accumulated the attached edits. There are still far too many Unneeded Capitals On Words for my taste but I have not changed many of those. We could use some more opinions on that, I suppose. (if it becomes too silent maybe include the pgsql-hackers again?) Thanks, Erik Rijkers -- Jürgen Purtz --- doc/src/sgml/architecture.sgml.orig 2020-07-17 16:24:04.345941142 +0200 +++ doc/src/sgml/architecture.sgml 2020-07-18 19:04:30.694039877 +0200 @@ -4,36 +4,36 @@ Architectural and implementational Cornerstones - Every DBMS implements basic strategies to achieve a fast and + Every DBMS implements basic strategies for a fast and robust system. This chapter provides an overview of what techniques PostgreSQL uses to - reach this aim. + achieve this. Collaboration of Processes, RAM, and Files -As is a matter of course, in a client/server architecture +In a client/server architecture clients do not have direct access to the database. Instead, -they merely send requests to the server-side and receive -according information from there. In the case of +they send requests to the server and receive +the requested information. In the case of PostgreSQL, at the server-side there is one process per client, the so-called Backend process. It acts in close cooperation with the Instance which -is a group of tightly coupled other server-side processes plus a +is a group of server-side processes plus a Shared Memory area. -At start time, an instance is initiated by the -Postmaster +At startup time, an instance is initiated by the +postmaster process. -It loads the configuration files, allocates the +The postmaster process loads the configuration files, allocates Shared Memory, -and starts the comprehensive network of processes: +and starts a network of processes: Background Writer, Checkpointer, WAL Writer, @@ -65,8 +65,8 @@ Whenever a client application tries to connect to a database, this request is handled in a first step by the -Postgres process. It checks the authorization, -starts a new Backend process, +postgres process. It checks authorization, +starts a new backend process, and instructs the client application to connect to it. All further client requests go to this process and are handled by it. @@ -83,20 +83,20 @@ index files. Because files are often larger than memory, it's likely that the desired information is not (completely) available -in the RAM. In this case the Backend process +in RAM. In this case the Backend process must transfer additional file pages to Shared Memory. Files are physically organized in pages. Every transfer between files and -RAM is performed in units of complete pages. Such transfers -don't change the size or layout of pages. +RAM is performed in units of complete pages; such transfers +do not change the size or layout of pages. -Reading file pages is notedly slower than reading -RAM. This is the primary motivation for the existence of +Reading file pages is much slower than reading +RAM. This is the primary motivation for the usage of Shared Memory. As soon as one of the Backend processes has -read pages into memory, those pages are available for all +read pages into memory, those pages become available for all other Backend processes for direct access in RAM. @@ -121,13 +121,13 @@ First, whenever the content of a page changes, a WAL record is created out -of the delta-information (difference between old and -new content) and stored in another area of the +of the delta-information (difference between the old and +the new content) and stored in another area of Shared Memory. These WAL records are read by the WAL Writer process, which runs in parallel to the Backend -processes and all other processes of +processes and other processes of the Instance. It writes the continuously arising WAL records to the end of the current @@ -137,7 +137,7 @@ to data files with heap and index information. As mentioned, this WAL-writing happens -in an independent process. Nevertheless, all +in an independent process. All WAL records created out of one dirty page must be transferred to disk before the dirty page @@ -146,35 +146,34 @@ Second, the transfer of dirty buffers -from Shared Memory to files must -take
Re: Additional Chapter for Tutorial
> On 13 Jul 2020, at 14:20, Naresh gandi wrote: (please avoid top-posting) > Which version is this application for? > > I tried for v12 and v13 Beta, both failed. Unless being a bugfix, all patches are only considered against the main development branch in Git. As this is new material, it would be for v14. cheers ./daniel
Re: Additional Chapter for Tutorial
Which version is this application for? I tried for v12 and v13 Beta, both failed. Regards, Naresh G On Mon, Jul 13, 2020 at 11:45 AM Jürgen Purtz wrote: > > On 12.07.20 22:45, Daniel Gustafsson wrote: > > This patch no longer applies, due to conflicts in start.sgml, can you > please > > submit a rebased version? > > ok. but I need some days. juergen > > > > >
Re: Additional Chapter for Tutorial
On 12.07.20 22:45, Daniel Gustafsson wrote: This patch no longer applies, due to conflicts in start.sgml, can you please submit a rebased version? ok. but I need some days. juergen
Re: Additional Chapter for Tutorial
> On 2 Jun 2020, at 17:01, Jürgen Purtz wrote: > In comparison with to previous patch this one contains: > > - Position and title changed to reflect its intention and importance. > > - A delimits VACUUM basics from details. This is done because I cannot > find another suitable place for such a summarizing description. > > - Three additional sub-chapters. This patch no longer applies, due to conflicts in start.sgml, can you please submit a rebased version? cheers ./daniel
Re: Additional Chapter for Tutorial
On 29.04.20 21:12, Peter Eisentraut wrote: I don't see this really as belonging into the tutorial. The tutorial should be hands-on, how do you get started, how do you get some results. Yes, the tutorial should be a short overview and give instructions how to start. IMO the first 4 sub-chapters fulfill this expectation. Indeed, the fifth (VACUUM) is extensive and offers many details. During the inspection of the existing documentation I recognized that there are many details about VACUUM, AUTOVACUUM, all of their parameters as well as their behavior. But the information is spread across many pages: Automatic Vacuuming, Client Connection Defaults, Routine Vacuuming, Resource Consumption, VACUUM. Even for a person with some pre-knowledge it is hard to get an overview how this fits together and why things are solved in exactly this way. In the end we have very good descriptions of all details but I miss the 'big picture'. Therefore I summarized central aspects and tried to give an answer to the question 'why is it done in this way?'. I do not dispute that the current version of the page is not adequate for beginners. But at some place we should have such a summary about vacuuming and freezing. How to proceed? - Remove the page and add a short paragraph to the MVCC page instead. - Cut down the page to a tiny portion. - Divide it into two parts: a) a short introduction and b) the rest after a statement like 'The following offers more details and parameters that are more interesting for an experienced user than for a beginner. You can easily skip it.' Your material is more of an overview of the whole system. What's a new user supposed to do with that? When I dive into a new subject, I'm more interested in its architecture than in its details. We shall offer an overview about the major PG components and strategies to beginners. -- Jürgen Purtz
Re: Additional Chapter for Tutorial
On 2020-04-29 16:13, Jürgen Purtz wrote: On 20.04.20 10:30, Jürgen Purtz wrote: On 17.04.20 20:40, Erik Rijkers wrote: Very good stuff, and useful. I think. I mean that but nevertheless here is a lot of comment :) (I didn't fully compile as docs, just read the 'text' from the patch file) Thanks. Added nearly all of the suggestions. What is new? Added two sub-chapters 'mvcc' and 'vacuum' plus graphics. Made some modifications in previous sub-chapters and in existing titles. Added some glossary entries. I don't see this really as belonging into the tutorial. The tutorial should be hands-on, how do you get started, how do you get some results. Your material is more of an overview of the whole system. What's a new user supposed to do with that? -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
Re: Additional Chapter for Tutorial - (review first half of 0003)
On 2020-04-29 16:13, Jürgen Purtz wrote: On 20.04.20 10:30, Jürgen Purtz wrote: On 17.04.20 20:40, Erik Rijkers wrote: Very good stuff, and useful. I think. I mean that but nevertheless here is a lot of comment :) (I didn't fully compile as docs, just read the 'text' from the patch file) Thanks. Added nearly all of the suggestions. What is new? Added two sub-chapters 'mvcc' and 'vacuum' plus graphics. Made some modifications in previous sub-chapters and in existing titles. Added some glossary entries. [0003-architecture.patch] Hi Jürgen, Here are again some suggested changes, up to line 600 (of the patch - that is around start of the new NVCC paragraph) I may have repeated some thing you have already rejected (it was too much work to go back and check). I am not a native speaker of english. One general remark: in my humble opinion, you write too many capitalized words. It's not really a problem but overall it's becomes bit too much. But I have not marked these. perhaps some future iteration. I'll probably read through the latter part of the patch later (probably tomorrow). Thanks, Erik Rijkers they merely send requests to the server side and receives they merely send requests to the server side and receive is a group of tightly coupled other server side processes plus a is a group of tightly coupled other server-side processes plus a Client requests (SELECT, UPDATE, ...) usually leads to the Client requests (SELECT, UPDATE, ...) usually lead to the Because files are much larger than memory, it's likely that Because files are often larger than memory, it's likely that RAM is performed in units of complete pages, retaining their size and layout. RAM is performed in units of complete pages. Reading file pages is notedly slower than reading Reading file pages is slower than reading of the Backend processes has done the job those pages are available for all other of the Backend processes has read pages into memory those pages are available for all other they must be transferred back to disk. This is a two-step process. they must be written back to disk. This is a two-step process. Because of the sequential nature of this writing, it is much Because of this writing is sequential, it is much in an independent process. Nevertheless all in an independent process. Nevertheless, all huge I/O activities can block other processes significantly, I/O activities can block other processes, it starts periodically and acts only for a short period. it starts periodically and is active only for a short period. duty. As its name suggests, he has to create duty. As its name suggests, it has to create In consequence, after a Checkpoint After a Checkpoint, In correlation with data changes, As a result of data changes, text lines about serious and non-serious events which can happen text lines about serious and less serious events which can happen database contains many linkend="glossary-schema">schema, database contains many linkend="glossary-schema">schemas, belongs to a certain schema, they cannot belongs to a single schema, they cannot A Cluster is the outer frame for a A Cluster is the outer container for a postgres as a copy of postgres is generated as a copy of role of template0 as the origin role of template0 as the pristine origin are different objects and absolutely independent from each are different objects and independent from each complete cluster, independent from cluster, independent from anywhere in the file system. In many cases, the environment somewhere in the file system. In many cases, the environment some files, all of which are necessary to store long lasting some files, all of which are necessary to store long-lasting tablespaces itself. tablespaces themselves. Postgres (respectively Postmaster) process. Postgres process (also known as Postmaster). MVCC MVCC - Multiversion Concurrency Control The dabase must take a sensible decision to prevent the application The database must take a sensible decision to prevent the application # this sentence I just don't understand - can you please elucidate? The database must take a sensible decision to prevent the application from promising delivery of the single article to both clients.
Re: Additional Chapter for Tutorial
On 17.04.20 20:40, Erik Rijkers wrote: Very good stuff, and useful. I think. I mean that but nevertheless here is a lot of comment :) (I didn't fully compile as docs, just read the 'text' from the patch file) Thanks. Added nearly all of the suggestions. -- Jürgen Purtz diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml index ae5f3fac75..965eb751c0 100644 --- a/doc/src/sgml/advanced.sgml +++ b/doc/src/sgml/advanced.sgml @@ -1,7 +1,7 @@ - Advanced Features + Advanced SQL Features Introduction diff --git a/doc/src/sgml/architecture.sgml b/doc/src/sgml/architecture.sgml new file mode 100644 index 00..81dedc90b4 --- /dev/null +++ b/doc/src/sgml/architecture.sgml @@ -0,0 +1,449 @@ + + + + The Architecture + + + Every DBMS implements basic strategies to achieve a fast and + robust system. This chapter provides an overview of what + techniques PostgreSQL uses to + reach this aim. + + + + Collaboration of Processes, RAM, and Files + +As is a matter of course, in a client/server architecture +clients do not have direct access to the database. Instead, +they merely send requests to the server side and receives +according information from there. In the case of +PostgreSQL, at the server +side there is one process per client, the so-called +Backend process. +It acts in close cooperation with the +Instance which +is a group of tightly coupled other server side processes plus a +Shared Memory +area. + + + +At start time, an instance is initiated by the +Postmaster process. +It loads the configuration files, allocates the +Shared Memory +and starts the comprehensive network of processes: +Background Writer, +Checkpointer, +WAL Writer, +WAL Archiver, +Autovacuum processes, +Statistics Collector, +Logger, and more. + visualizes +main aspects of their collaboration. + + + +Architecture + + + + + + + + + + + + + +Whenever a client application tries to connect to a +database, this request is handled +in a first step by the Postmaster +process. It checks the authorization, starts a +new Backend process, +and instructs the client application to connect to it. All further +client requests go to this process and are handled +by it. + + + +Client requests (SELECT, UPDATE, ...) usually leads to the +necessity to read or write some data. In a first attempt +the client's Backend process tries +to get the information out of Shared +Memory. This Shared +Memory is a mirror of parts of the +heap and +index files. Because files are +much larger than memory, it's likely that +the desired information is not (completely) available +in the RAM. In this case the Backend process + must transfer additional file pages to +Shared Memory. Files are physically +organized in pages. Every transfer between files and +RAM is performed in units of complete pages, retaining +their size and layout. + + + +Reading file pages is notedly slower than reading +RAM. This is the main motivation for the existence of +Shared Memory. As soon as one +of the Backend processes has done +the job those pages are available for all other +Backend processes for direct +access in RAM. + + + +Shared Memory is limited in size. +Sooner or later it becomes necessary to overwrite old RAM +pages. As long as the content of such pages hasn't +changed this is not a problem. But in +Shared Memory also write +actions take place +- performed by any of the Backend +processes (or an +autovacuum process, +or other processes). Such modified pages are called +dirty pages. +Before dirty pages can be overwritten, +they must be transferred back to disk. This is a two-step process. + + + +First, whenever the content of a page changes, a +WAL record is created out +of the delta-information (difference between old and +new content) and stored in another area of the +Shared Memory. These +WAL records are read by the +WAL Writer process, +which runs in parallel to the Backend +processes and all other processes of +the Instance. It writes +the continuously arising WAL records to +the end of the current +WAL file. +Because of the sequential nature of this writing, it is much +faster than the more or less random access +to data files with heap +and index information. +As mentioned, this WAL-writing happens +in an independent process. Nevertheless all +WAL records created out of one +dirty page must be transferred +to disk before the dirty page +itself can be transferred to disk (???). + + + +Second, the transfer of dirty pages +from Shared Memory to
Re: Additional Chapter for Tutorial
On 2020-04-17 19:56, Jürgen Purtz wrote: Our documentation explains many details about commands, tools, parameters in detail and with high accuracy. Nevertheless my impression is that we neglect the 'big picture': why certain processes [0001-architecture.patch] Very good stuff, and useful. I think. I mean that but nevertheless here is a lot of comment :) (I didn't fully compile as docs, just read the 'text' from the patch file) Collabortion Collaboration drop 'resulting' He acts in close cooperation with the It acts in close cooperation with the He loads the configuration files, allocates the It loads the configuration files, allocates the process. He checks the authorization, starts a process. it checks the authorization, starts a and instructs the client application to connect to him. All further and instructs the client application to connect to it. All further by him. by it. In an first attempt In a first attempt much huger than memory, it's likely that much larger than memory, it's likely that RAM is performed in units of complete pages while retaining RAM is performed in units of complete pages, retaining Sooner or later it is necessary to overwrite old RAM Sooner or later it becomes necessary to overwrite old RAM transfered transferred (multiple times) who runs which runs He writes it writes This is the primarily duty of the This is primarily the duty of the or possibly: This is the primary duty of the he starts periodically it starts periodically speeds up a possibly occurring recovery. can speed up recovery. writen written collects counter about accesses collects counters about accesses and others. He stores the obtained information in system and more. It stores the obtained information in system sudirectories consists subdirectories consist <-- plural, no -s there are information there is information and contains the ID of the and contains the ID (pid) of the ( IMHO, it is conventional (and therefore easier to read) to have 'e.g.' followed by a comma, and not by a semi-colon, although obviously that's not really wrong either. ) Thanks, Erik Rijkers
Re: Additional Chapter for Tutorial
> > I plan to extend over time the part 'Tutorial' by an additional chapter > with an overview about key design decisions and basic features. The > typical audience should consist of persons with limited pre-knowledge in > database systems and some interest in PostgreSQL. In the attachment you > find a patch for the first sub-chapter. Subsequent sub-chapters should > be: MVCC, transactions, VACUUM, backup, replication, ... - mostly with > the focus on the PostgreSQL implementation and not on generic topics > like b-trees. > +1
