From: Jerry Sievers <gsievers19@comcast.net>
To: None <espressobeanies@gmail.com>
Cc: pgsql-docs@postgresql.org
Subject: Re: Need help finding all possible parameters for wal_level
References: 
 <CAOeD16_bRY_mDqtjb-bOHua_jw6utswEzYjwkEL3VEP3UMSmwA@mail.gmail.com>
Date: Fri, 01 Sep 2017 09:54:23 -0500
In-Reply-To: 
 <CAOeD16_bRY_mDqtjb-bOHua_jw6utswEzYjwkEL3VEP3UMSmwA@mail.gmail.com>
	(None's message of "Fri, 1 Sep 2017 10:36:13 -0400")
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None <espressobeanies@gmail.com> writes:

> Hi,
>
> I'm searching for all of the possible parameters for setting the
> "wal_level" outlined in the PostgreSQL Streaming Replication article:
>
> https://wiki.postgresql.org/wiki/Streaming_Replication
>
> I currently see hot_standby, but I can't find a list for all of the
> parameters that setting will take. Where can I find that?

You didn't even tell us what version is relevant here but let's assume 9.6...


https://www.postgresql.org/docs/9.6/static/runtime-config-wal.html


wal_level (enum)
   
    wal_level determines how much information is written to the WAL. The default value is minimal, which writes only the information needed to recover from a crash or immediate shutdown.
    replica adds logging required for WAL archiving as well as information required to run read-only queries on a standby server. Finally, logical adds information necessary to support
    logical decoding. Each level includes the information logged at all lower levels. This parameter can only be set at server start.
   
    In minimal level, WAL-logging of some bulk operations can be safely skipped, which can make those operations much faster (see Section 14.4.7). Operations in which this optimization can
    be applied include:
   
    CREATE TABLE AS                                                        
    CREATE INDEX                                                           
    CLUSTER                                                                
    COPY into tables that were created or truncated in the same transaction
   
    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 (archive_mode)
    and streaming replication.
   
    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 logical will increase the
    WAL volume, particularly if many tables are configured for REPLICA IDENTITY FULL and many UPDATE and DELETE statements are executed.
   
    In releases prior to 9.6, this parameter also allowed the values archive and hot_standby. These are still accepted but mapped to replica.


>
> Thanks!
>
>

-- 
Jerry Sievers
Postgres DBA/Development Consulting
e: postgres.consulting@comcast.net
p: 312.241.7800


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