Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Mon, Jul 18, 2022 at 11:16:15PM -0400, Bruce Momjian wrote: > On Mon, Jul 18, 2022 at 07:39:55PM -0700, David G. Johnston wrote: > > On Mon, Jul 18, 2022 at 6:27 PM Japin Li wrote: > > > > > > +0.90 > > > > Consider changing: > > > > "makes any base backups taken before this unusable" > > > > to: > > > > "makes existing base backups unusable" > > > > As I try to justify this, though, it isn't quite true, maybe: > > > > "makes point-in-time recovery, using existing base backups, unable to replay > > future WAL." > > I went with simpler wording. Patch applied back to PG 14, and partial to PG 13. Docs before that were too different to be safe. -- Bruce Momjian https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Mon, Jul 18, 2022 at 8:16 PM Bruce Momjian wrote: > On Mon, Jul 18, 2022 at 07:39:55PM -0700, David G. Johnston wrote: > > On Mon, Jul 18, 2022 at 6:27 PM Japin Li wrote: > > > > > > +0.90 > > > > Consider changing: > > > > "makes any base backups taken before this unusable" > > > > to: > > > > "makes existing base backups unusable" > > > > As I try to justify this, though, it isn't quite true, maybe: > > > > "makes point-in-time recovery, using existing base backups, unable to > replay > > future WAL." > > I went with simpler wording. > > +1 Thanks! David J.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Mon, Jul 18, 2022 at 07:39:55PM -0700, David G. Johnston wrote: > On Mon, Jul 18, 2022 at 6:27 PM Japin Li wrote: > > > +0.90 > > Consider changing: > > "makes any base backups taken before this unusable" > > to: > > "makes existing base backups unusable" > > As I try to justify this, though, it isn't quite true, maybe: > > "makes point-in-time recovery, using existing base backups, unable to replay > future WAL." I went with simpler wording. -- Bruce Momjian https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 37fd80388c..c2bdacb6a7 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2764,9 +2764,10 @@ include_dir 'conf.d' levels. This parameter can only be set at server start. -In minimal level, no information is logged for -permanent relations for the remainder of a transaction that creates or -rewrites them. This can make operations much faster (see +The minimal level generates the least WAL +volume. It logs no row information for permanent relations +in transactions that create or +rewrite them. This can make operations much faster (see ). Operations that initiate this optimization include: @@ -2778,19 +2779,20 @@ include_dir 'conf.d' REINDEX TRUNCATE -But minimal WAL does not contain enough information to reconstruct the -data from a base backup and the WAL logs, so replica or -higher must be used to enable WAL archiving -() and streaming replication. +However, minimal WAL does not contain sufficient information for +point-in-time recovery, so replica or +higher must be used to enable continuous archiving +() and streaming binary replication. +In fact, the server will not even start in this mode if +max_wal_senders is non-zero. Note that changing wal_level to -minimal makes any base backups taken before -unavailable for archive recovery and standby server, which may -lead to data loss. +minimal makes previous base backups unusable +for point-in-time recovery and standby servers. In logical level, the same information is logged as -with replica, plus information needed to allow -extracting logical change sets from the WAL. Using a level of +with replica, plus information needed to +extract logical change sets from the WAL. Using a level of logical will increase the WAL volume, particularly if many tables are configured for REPLICA IDENTITY FULL and many UPDATE and DELETE statements are
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Mon, Jul 18, 2022 at 6:27 PM Japin Li wrote: > > On Tue, 19 Jul 2022 at 03:58, Bruce Momjian wrote: > > On Fri, Jul 15, 2022 at 09:29:20PM +0800, Japin Li wrote: > >> > >> On Fri, 15 Jul 2022 at 08:49, Bruce Momjian wrote: > >> > On Tue, Jul 5, 2022 at 08:02:33PM -0400, Tom Lane wrote: > >> >> "Precondition" is an overly fancy word that makes things less clear > >> >> not more so. Does it mean that setting wal_level = minimal will fail > >> >> if you don't do these other things, or does it just mean that you > >> >> won't be getting the absolute minimum WAL volume? If the former, > >> >> I think it'd be better to say something like "To set wal_level to > minimal, > >> >> you must also set [these variables], which has the effect of > disabling > >> >> both WAL archiving and streaming replication." > >> > > >> > I have created the attached patch to try to improve this text. > >> > >> IMO we can add the following sentence for wal_level description, since > >> if wal_level = minimal and max_wal_senders > 0, we cannot start the > database. > >> > >> To set wal_level to minimal, you must also set max_wal_senders to 0, > >> which has the effect of disabling both WAL archiving and streaming > >> replication. > > > > Okay, text added in the attached patch. > > Thanks for updating the patch! LGTM. > > +0.90 Consider changing: "makes any base backups taken before this unusable" to: "makes existing base backups unusable" As I try to justify this, though, it isn't quite true, maybe: "makes point-in-time recovery, using existing base backups, unable to replay future WAL." David J.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Tue, 19 Jul 2022 at 03:58, Bruce Momjian wrote: > On Fri, Jul 15, 2022 at 09:29:20PM +0800, Japin Li wrote: >> >> On Fri, 15 Jul 2022 at 08:49, Bruce Momjian wrote: >> > On Tue, Jul 5, 2022 at 08:02:33PM -0400, Tom Lane wrote: >> >> "Precondition" is an overly fancy word that makes things less clear >> >> not more so. Does it mean that setting wal_level = minimal will fail >> >> if you don't do these other things, or does it just mean that you >> >> won't be getting the absolute minimum WAL volume? If the former, >> >> I think it'd be better to say something like "To set wal_level to minimal, >> >> you must also set [these variables], which has the effect of disabling >> >> both WAL archiving and streaming replication." >> > >> > I have created the attached patch to try to improve this text. >> >> IMO we can add the following sentence for wal_level description, since >> if wal_level = minimal and max_wal_senders > 0, we cannot start the database. >> >> To set wal_level to minimal, you must also set max_wal_senders to 0, >> which has the effect of disabling both WAL archiving and streaming >> replication. > > Okay, text added in the attached patch. Thanks for updating the patch! LGTM. -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Fri, Jul 15, 2022 at 09:29:20PM +0800, Japin Li wrote: > > On Fri, 15 Jul 2022 at 08:49, Bruce Momjian wrote: > > On Tue, Jul 5, 2022 at 08:02:33PM -0400, Tom Lane wrote: > >> "Precondition" is an overly fancy word that makes things less clear > >> not more so. Does it mean that setting wal_level = minimal will fail > >> if you don't do these other things, or does it just mean that you > >> won't be getting the absolute minimum WAL volume? If the former, > >> I think it'd be better to say something like "To set wal_level to minimal, > >> you must also set [these variables], which has the effect of disabling > >> both WAL archiving and streaming replication." > > > > I have created the attached patch to try to improve this text. > > IMO we can add the following sentence for wal_level description, since > if wal_level = minimal and max_wal_senders > 0, we cannot start the database. > > To set wal_level to minimal, you must also set max_wal_senders to 0, > which has the effect of disabling both WAL archiving and streaming > replication. Okay, text added in the attached patch. -- Bruce Momjian https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 37fd80388c..4c0489c9c3 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2764,9 +2764,10 @@ include_dir 'conf.d' levels. This parameter can only be set at server start. -In minimal level, no information is logged for -permanent relations for the remainder of a transaction that creates or -rewrites them. This can make operations much faster (see +The minimal level generates the least WAL +volume. It logs no row information for permanent relations +in transactions that create or +rewrite them. This can make operations much faster (see ). Operations that initiate this optimization include: @@ -2778,19 +2779,20 @@ include_dir 'conf.d' REINDEX TRUNCATE -But minimal WAL does not contain enough information to reconstruct the -data from a base backup and the WAL logs, so replica or -higher must be used to enable WAL archiving -() and streaming replication. +However, minimal WAL does not contain sufficient information for +point-in-time recovery, so replica or +higher must be used to enable continuous archiving +() and streaming binary replication. +In fact, the server will not even start in this mode if +max_wal_senders is non-zero. Note that changing wal_level to -minimal makes any base backups taken before -unavailable for archive recovery and standby server, which may -lead to data loss. +minimal makes any base backups taken before this +unusable for point-in-time recovery and standby servers. In logical level, the same information is logged as -with replica, plus information needed to allow -extracting logical change sets from the WAL. Using a level of +with replica, plus information needed to +extract logical change sets from the WAL. Using a level of logical will increase the WAL volume, particularly if many tables are configured for REPLICA IDENTITY FULL and many UPDATE and DELETE statements are
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Fri, Jul 15, 2022 at 6:27 AM Japin Li wrote: > > > > > +servers. If setting max_wal_senders to > > +0 consider also reducing the amount of WAL > produced > > +by changing wal_level to > minimal. > > > > I don't think this is great advice. It will encourage people to use > > wal_level = minimal even if they have other requirements that weigh > > against it. If they feel that their system is producing too much > > WAL, I doubt they'll have a hard time finding the wal_level knob. > > > > Agreed. It isn't good advice. We can remove the suggestion. > > Yeah, I wrote that thinking that max_wal_senders being set to 0 implied archive_mode = off, but that isn't the case. David J.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Fri, 15 Jul 2022 at 08:49, Bruce Momjian wrote: > On Tue, Jul 5, 2022 at 08:02:33PM -0400, Tom Lane wrote: >> "Precondition" is an overly fancy word that makes things less clear >> not more so. Does it mean that setting wal_level = minimal will fail >> if you don't do these other things, or does it just mean that you >> won't be getting the absolute minimum WAL volume? If the former, >> I think it'd be better to say something like "To set wal_level to minimal, >> you must also set [these variables], which has the effect of disabling >> both WAL archiving and streaming replication." > > I have created the attached patch to try to improve this text. IMO we can add the following sentence for wal_level description, since if wal_level = minimal and max_wal_senders > 0, we cannot start the database. To set wal_level to minimal, you must also set max_wal_senders to 0, which has the effect of disabling both WAL archiving and streaming replication. -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
Sorry for the late reply. On Wed, 06 Jul 2022 at 08:02, Tom Lane wrote: > Japin Li writes: >> [ v4-wal-level-documentation.patch ] > > Hm, I don't care for the wording here: > > +A precondition for using minimal WAL is to disable WAL archiving and > +streaming replication by setting archive_mode to > +off, and to > +0. > > "Precondition" is an overly fancy word that makes things less clear > not more so. Does it mean that setting wal_level = minimal will fail > if you don't do these other things, or does it just mean that you > won't be getting the absolute minimum WAL volume? If the former, > I think it'd be better to say something like "To set wal_level to minimal, > you must also set [these variables], which has the effect of disabling > both WAL archiving and streaming replication." Yeah, it's the former case. > > +servers. If setting max_wal_senders to > +0 consider also reducing the amount of WAL > produced > +by changing wal_level to > minimal. > > I don't think this is great advice. It will encourage people to use > wal_level = minimal even if they have other requirements that weigh > against it. If they feel that their system is producing too much > WAL, I doubt they'll have a hard time finding the wal_level knob. > Agreed. It isn't good advice. We can remove the suggestion. -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Tue, Jul 5, 2022 at 08:02:33PM -0400, Tom Lane wrote: > "Precondition" is an overly fancy word that makes things less clear > not more so. Does it mean that setting wal_level = minimal will fail > if you don't do these other things, or does it just mean that you > won't be getting the absolute minimum WAL volume? If the former, > I think it'd be better to say something like "To set wal_level to minimal, > you must also set [these variables], which has the effect of disabling > both WAL archiving and streaming replication." I have created the attached patch to try to improve this text. -- Bruce Momjian https://momjian.us EDB https://enterprisedb.com Indecision is a decision. Inaction is an action. Mark Batterson diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 37fd80388c..964f9fb379 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2764,9 +2764,10 @@ include_dir 'conf.d' levels. This parameter can only be set at server start. -In minimal level, no information is logged for -permanent relations for the remainder of a transaction that creates or -rewrites them. This can make operations much faster (see +The minimal level generates the least WAL +volume. It logs no row information for permanent relations +in transactions that create or +rewrite them. This can make operations much faster (see ). Operations that initiate this optimization include: @@ -2778,19 +2779,18 @@ include_dir 'conf.d' REINDEX TRUNCATE -But minimal WAL does not contain enough information to reconstruct the -data from a base backup and the WAL logs, so replica or -higher must be used to enable WAL archiving -() and streaming replication. +However, minimal WAL does not contain sufficient information for +point-in-time recovery, so replica or +higher must be used to enable continuous archiving +() and streaming binary replication. Note that changing wal_level to -minimal makes any base backups taken before -unavailable for archive recovery and standby server, which may -lead to data loss. +minimal makes any base backups taken before this +unusable for point-in-time recovery and standby servers. In logical level, the same information is logged as -with replica, plus information needed to allow -extracting logical change sets from the WAL. Using a level of +with replica, plus information needed to +extract logical change sets from the WAL. Using a level of logical will increase the WAL volume, particularly if many tables are configured for REPLICA IDENTITY FULL and many UPDATE and DELETE statements are
Re: Doc about how to set max_wal_senders when setting minimal wal_level
Japin Li writes: > [ v4-wal-level-documentation.patch ] Hm, I don't care for the wording here: +A precondition for using minimal WAL is to disable WAL archiving and +streaming replication by setting archive_mode to +off, and to +0. "Precondition" is an overly fancy word that makes things less clear not more so. Does it mean that setting wal_level = minimal will fail if you don't do these other things, or does it just mean that you won't be getting the absolute minimum WAL volume? If the former, I think it'd be better to say something like "To set wal_level to minimal, you must also set [these variables], which has the effect of disabling both WAL archiving and streaming replication." +servers. If setting max_wal_senders to +0 consider also reducing the amount of WAL produced +by changing wal_level to minimal. I don't think this is great advice. It will encourage people to use wal_level = minimal even if they have other requirements that weigh against it. If they feel that their system is producing too much WAL, I doubt they'll have a hard time finding the wal_level knob. TBH, I think the real problem with the docs in this area is that the first para about wal_level is disjointed and unclear; we ought to nuke and rewrite that. In particular it fails to provide adequate context about what "logical decoding" means. I think possibly what it needs to say is that replica mode supports *physical* replication but if you want to use *logical* replication you need logical mode; if you need neither, and are not doing WAL archiving either, you can get away with minimal mode. regards, tom lane
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Fri, Mar 4, 2022 at 2:49 AM Japin Li wrote: > Thanks for your review. Modified. > Works for me. I have some additional sparks of ideas but nothing that need hold this up. David J.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Thu, Mar 3, 2022 at 11:05 PM Kyotaro Horiguchi wrote: > But, > anyway, IMHO, it is mere a performance tips that is not necessarily > required in this section, or even in this documentaiotn. Addtion to > that, if we write this for max_wal_senders, archive_mode will deserve > the similar tips but I think it is too verbose. In short, I think I > would not add that description at all. > > I wrote it as a performance tip but it is documenting that when set to 0 no features of the server require more information than is captured in the minimal wal. That fact seems worthy of noting. Even at the cost of a bit of verbosity. These features interact with each other and that interaction should be adequately described. While subjective, this dynamic seems to warrant inclusion. David J.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Fri, 04 Mar 2022 at 14:05, Kyotaro Horiguchi wrote: > At Fri, 04 Mar 2022 12:18:29 +0800, Japin Li wrote in >> >> On Thu, 03 Mar 2022 at 12:10, Japin Li wrote: >> >> Attach v3 patch to fix missing close varname tag. > > +A precondition for using minimal WAL is to disable WAL archiving and > +streaming replication by setting linkend="guc-max-wal-senders"/> > +to 0, and archive_mode > +to off. > > It is a bit odd that the features to stop and the corresponding GUCs > are written irrespectively. It would be better they're in the same > order. > Thanks for your review. Modified. > +servers. If setting max_wal_senders to > +0 consider also reducing the amount of WAL > produced > +by changing wal_level to > minimal. > > Those who anively follow this suggestion may bump into failure when > arhive_mode is on. Thus archive_mode is also worth referred to. But, > anyway, IMHO, it is mere a performance tips that is not necessarily > required in this section, or even in this documentaiotn. Addtion to > that, if we write this for max_wal_senders, archive_mode will deserve > the similar tips but I think it is too verbose. In short, I think I > would not add that description at all. > It already has a tip about wal_level for archive_mode [1], IIUC. archive_mode cannot be enabled when wal_level is set to minimal. [1] https://www.postgresql.org/docs/devel/runtime-config-wal.html#GUC-ARCHIVE-MODE -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd. diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 7ed8c82a9d..a70adb7030 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2775,6 +2775,10 @@ include_dir 'conf.d' minimal makes any base backups taken before unavailable for archive recovery and standby server, which may lead to data loss. +A precondition for using minimal WAL is to disable WAL archiving and +streaming replication by setting archive_mode to +off, and to +0. In logical level, the same information is logged as @@ -3535,6 +3539,7 @@ include_dir 'conf.d' mode. In always mode, all files restored from the archive or streamed with streaming replication will be archived (again). See for details. +The default value is off. This parameter can only be set at server start. @@ -4096,7 +4101,9 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows reconnect. This parameter can only be set at server start. Also, wal_level must be set to replica or higher to allow connections from standby -servers. +servers. If setting max_wal_senders to +0 consider also reducing the amount of WAL produced +by changing wal_level to minimal.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
At Fri, 04 Mar 2022 12:18:29 +0800, Japin Li wrote in > > On Thu, 03 Mar 2022 at 12:10, Japin Li wrote: > > Attach v3 patch to fix missing close varname tag. +A precondition for using minimal WAL is to disable WAL archiving and +streaming replication by setting +to 0, and archive_mode +to off. It is a bit odd that the features to stop and the corresponding GUCs are written irrespectively. It would be better they're in the same order. +servers. If setting max_wal_senders to +0 consider also reducing the amount of WAL produced +by changing wal_level to minimal. Those who anively follow this suggestion may bump into failure when arhive_mode is on. Thus archive_mode is also worth referred to. But, anyway, IMHO, it is mere a performance tips that is not necessarily required in this section, or even in this documentaiotn. Addtion to that, if we write this for max_wal_senders, archive_mode will deserve the similar tips but I think it is too verbose. In short, I think I would not add that description at all. regards. -- Kyotaro Horiguchi NTT Open Source Software Center
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Thu, 03 Mar 2022 at 12:10, Japin Li wrote: > On Thu, 03 Mar 2022 at 11:25, David G. Johnston > wrote: >> I would suggest a wording more like: >> >> "A precondition for using minimal WAL is to disable WAL archiving and >> streaming replication by setting max_wal_senders to 0, and archive_mode to >> off." >> >> While accurate, the phrase "you must set" just doesn't feel right to me. I >> also don't like how the proposed sentence (either one) is added separately >> as opposed to being included in the immediately preceding paragraph. While >> this limited patch is probably sufficient I would suggest trying to work >> out a slightly larger patch the improves the wording on the entire existing >> paragraph while incorporating the reference to max_wal_senders. >> > > Thanks for your review. Modified as your suggestion. > >> Note, we seem to be missing the documentation of the default setting for >> archive_mode. >> > > Add the default value for archive_mode. > >> In addition, max_wal_senders could also be changed, adding a sentence like: >> >> "If setting max_wal_senders to 0 consider also reducing the amount of WAL >> produced by changing wal_level to minimal." >> > > Modified. Attach v3 patch to fix missing close varname tag. -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd. diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 7ed8c82a9d..bc7ba1e120 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2775,6 +2775,10 @@ include_dir 'conf.d' minimal makes any base backups taken before unavailable for archive recovery and standby server, which may lead to data loss. +A precondition for using minimal WAL is to disable WAL archiving and +streaming replication by setting +to 0, and archive_mode +to off. In logical level, the same information is logged as @@ -3535,6 +3539,7 @@ include_dir 'conf.d' mode. In always mode, all files restored from the archive or streamed with streaming replication will be archived (again). See for details. +The default value is off. This parameter can only be set at server start. @@ -4096,7 +4101,9 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows reconnect. This parameter can only be set at server start. Also, wal_level must be set to replica or higher to allow connections from standby -servers. +servers. If setting max_wal_senders to +0 consider also reducing the amount of WAL produced +by changing wal_level to minimal.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Thu, 03 Mar 2022 at 11:25, David G. Johnston wrote: > I would suggest a wording more like: > > "A precondition for using minimal WAL is to disable WAL archiving and > streaming replication by setting max_wal_senders to 0, and archive_mode to > off." > > While accurate, the phrase "you must set" just doesn't feel right to me. I > also don't like how the proposed sentence (either one) is added separately > as opposed to being included in the immediately preceding paragraph. While > this limited patch is probably sufficient I would suggest trying to work > out a slightly larger patch the improves the wording on the entire existing > paragraph while incorporating the reference to max_wal_senders. > Thanks for your review. Modified as your suggestion. > Note, we seem to be missing the documentation of the default setting for > archive_mode. > Add the default value for archive_mode. > In addition, max_wal_senders could also be changed, adding a sentence like: > > "If setting max_wal_senders to 0 consider also reducing the amount of WAL > produced by changing wal_level to minimal." > Modified. -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd. diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 7ed8c82a9d..4fd36fa53a 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2775,6 +2775,10 @@ include_dir 'conf.d' minimal makes any base backups taken before unavailable for archive recovery and standby server, which may lead to data loss. +A precondition for using minimal WAL is to disable WAL archiving and +streaming replication by setting +to 0, and archive_mode +to off. In logical level, the same information is logged as @@ -3535,6 +3539,7 @@ include_dir 'conf.d' mode. In always mode, all files restored from the archive or streamed with streaming replication will be archived (again). See for details. +The default value is off. This parameter can only be set at server start. @@ -4096,7 +4101,9 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows reconnect. This parameter can only be set at server start. Also, wal_level must be set to replica or higher to allow connections from standby -servers. +servers. If setting max_wal_senders to +0 consider also reducing the amount of WAL produced +by changing wal_level to minimal.
Re: Doc about how to set max_wal_senders when setting minimal wal_level
On Wed, Mar 2, 2022 at 7:44 PM Japin Li wrote: > > Hi, hackers > > When I try to change wal_level to minimal and restart the database, it > complains > max_wal_senders > 0. > > 2022-03-03 10:10:16.938 CST [6389] FATAL: WAL streaming (max_wal_senders > > 0) requires wal_level "replica" or "logical" > > However, the documentation about wal_level [1] doesn't mentation this. > How about adding a sentence to describe how to set max_wal_senders when > setting wal_level to minimal? > > [1] https://www.postgresql.org/docs/devel/runtime-config-wal.html > > I would suggest a wording more like: "A precondition for using minimal WAL is to disable WAL archiving and streaming replication by setting max_wal_senders to 0, and archive_mode to off." While accurate, the phrase "you must set" just doesn't feel right to me. I also don't like how the proposed sentence (either one) is added separately as opposed to being included in the immediately preceding paragraph. While this limited patch is probably sufficient I would suggest trying to work out a slightly larger patch the improves the wording on the entire existing paragraph while incorporating the reference to max_wal_senders. Note, we seem to be missing the documentation of the default setting for archive_mode. In addition, max_wal_senders could also be changed, adding a sentence like: "If setting max_wal_senders to 0 consider also reducing the amount of WAL produced by changing wal_level to minimal." At least insofar as core is concerned without a wal sender the additional wal of replica is not actually able to be leveraged as pg_basebackup will not work (at noted in its own description). David J.
Doc about how to set max_wal_senders when setting minimal wal_level
Hi, hackers When I try to change wal_level to minimal and restart the database, it complains max_wal_senders > 0. 2022-03-03 10:10:16.938 CST [6389] FATAL: WAL streaming (max_wal_senders > 0) requires wal_level "replica" or "logical" However, the documentation about wal_level [1] doesn't mentation this. How about adding a sentence to describe how to set max_wal_senders when setting wal_level to minimal? [1] https://www.postgresql.org/docs/devel/runtime-config-wal.html -- Regrads, Japin Li. ChengDu WenWu Information Technology Co.,Ltd. diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 7ed8c82a9d..3f5ecc4a04 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2776,6 +2776,10 @@ include_dir 'conf.d' unavailable for archive recovery and standby server, which may lead to data loss. + +When changing wal_level to minimal, +you must set the parameter to 0. + In logical level, the same information is logged as with replica, plus information needed to allow
