Обсуждение: Seek for helper documents to implement WAL with an FDW
Hi all,
I have written an FDW, which is similar to the file_fdw. I need the support of WAL to perform logical and stream replication. I have knowledge about custom WAL but do not have clarity about implementing WAL(writing, redo, desc, identify, etc..) and cases where WAL can be applied.
kindly share some documents, and links regarding WAL implementation.
Reference of Custom WAL: - https://www.postgresql.org/docs/current/custom-rmgr.html
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Komal Habura
On Tue, Feb 21, 2023 at 3:01 PM Komal Habura <komalhabura2@gmail.com> wrote: > > Hi all, > I have written an FDW, which is similar to the file_fdw. I need the support of WAL to perform logical and streamreplication. I have knowledge about custom WAL but do not have clarity about implementing WAL(writing, redo, desc,identify, etc..) and cases where WAL can be applied. > > kindly share some documents, and links regarding WAL implementation. > > Reference of Custom WAL: - https://www.postgresql.org/docs/current/custom-rmgr.html You can look at a sample extension called test_custom_rmgrs that implements custom WAL rmgr - https://git.postgresql.org/gitweb/?p=postgresql.git;a=tree;f=src/test/modules/test_custom_rmgrs;h=2144037578b01e56cbc8bf80af4fbdaa94c07c17;hb=HEAD. Basically, custom WAL rmgrs allow one to write WAL records of their own choice and define what to do when the server is in recovery i.e. replaying those WAL records or when the server is decoding (for logical replication) those WAL records. Coming to whether you need to write WAL at all in your FDW, it depends on what the FDW does. -- Bharath Rupireddy PostgreSQL Contributors Team RDS Open Source Databases Amazon Web Services: https://aws.amazon.com
On 20.02.23 10:53, Komal Habura wrote: > I have written an FDW, which is similar to the file_fdw. I need > the support of WAL to perform logical and stream replication. I have > knowledge about custom WAL but do not have clarity about implementing > WAL(writing, redo, desc, identify, etc..) and cases where WAL can be > applied. A foreign-data wrapper manages *foreign* data, which almost by definition means that it does not participate in the transaction management of the local PostgreSQL instance, including in the WAL. If you want to build a custom storage format that does participate in the local transaction management, you should probably look at building either a table access method or a storage manager.