Thread: What's difference among insert/write/flush lsn?

Hi,

pg_current_wal_flush_lsn()pg_lsnGet current write-ahead log flush location
pg_current_wal_insert_lsn()pg_lsnGet current write-ahead log insert location
pg_current_wal_lsn()pg_lsnGet current write-ahead log write location

I guess write is about how many bytes written in shared cache, and
flush is flush to file, which makes it persistent.

Anybody gives some official explanation?
Thanks.

Regards,
Jinhua Luo

On Sat, Feb  1, 2020 at 11:18:42AM +0800, Jinhua Luo wrote:
> Hi,
> 
> pg_current_wal_flush_lsn()pg_lsnGet current write-ahead log flush location
> pg_current_wal_insert_lsn()pg_lsnGet current write-ahead log insert location
> pg_current_wal_lsn()pg_lsnGet current write-ahead log write location
> 
> I guess write is about how many bytes written in shared cache, and
> flush is flush to file, which makes it persistent.
> 
> Anybody gives some official explanation?

I think the insert location is where data is being added to WAL, the
write location is where it was last written to the file system, and
flush is the last time is was flushed to storage.

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