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From: Kashif Zeeshan <kashi.zeeshan@gmail.com>
Date: Tue, 8 Apr 2025 17:01:38 +0500
Message-ID: <CAAPsdhdgwy4rgSUXAf_b+QVMtFyX2mKbfy6UwP=p824OWeMTBw@mail.gmail.com>
Subject: Re: Wal file query
To: Atul Kumar <akumar14871@gmail.com>
Cc: pgsql-general <pgsql-general@lists.postgresql.org>
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Hi Atul

Start by looking at the current WAL LSN and insert LSN. The
pg_current_wal_lsn is the location of the last write. The
pg_current_wal_insert_lsn is the logical location and reflects data in the
buffer that has not been written to disk. There is also a flush value that
shows what has been written to durable storage.

[postgres] # select pg_current_wal_lsn(), pg_current_wal_insert_lsn();
 pg_current_wal_lsn | pg_current_wal_insert_lsn
--------------------+---------------------------
 76/7D000000        | 76/7D000028
(1 row)

Although you can guess the name of the WAL file based on the above
output, it is best to use the pg_walfile_name function.


[postgres] # select pg_walfile_name('76/7D000028');
     pg_walfile_name
--------------------------
 00000001000000760000007D
(1 row)


For details visit following link :
https://www.crunchydata.com/blog/postgres-wal-files-and-sequuence-numbers


Thanks

Kashif Zeeshan


On Tue, Apr 8, 2025 at 4:44=E2=80=AFPM Atul Kumar <akumar14871@gmail.com> w=
rote:

> In streaming replication What is the way to check which "WAL file" is
> currently in use in primary  and in standby ?
>
>
> Regards.
>

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<div dir=3D"ltr">Hi=C2=A0Atul<div><br></div><div>Start by looking at the cu=
rrent WAL LSN and insert LSN. The <code>pg_current_wal_lsn</code> is the lo=
cation of the last write. The <code>pg_current_wal_insert_lsn</code>
 is the logical location and reflects data in the buffer that has not=20
been written to disk. There is also a flush value that shows what has=20
been written to durable storage.</div><div><pre><code class=3D"gmail-langua=
ge-shell gmail-hljs"></code></pre></div><div><pre><code class=3D"gmail-lang=
uage-shell gmail-hljs">[postgres] # select pg_current_wal_lsn(), pg_current=
_wal_insert_lsn();
 pg_current_wal_lsn | pg_current_wal_insert_lsn
--------------------+---------------------------
 76/7D000000        | 76/7D000028
(1 row)
</code></pre><pre><code class=3D"gmail-language-shell gmail-hljs">Although =
you can guess the name of the WAL file based on the above output, it is bes=
t to use the <code>pg_walfile_name</code> function.</code></pre><pre><code =
class=3D"gmail-language-shell gmail-hljs"><br></code></pre><pre><code class=
=3D"gmail-language-shell gmail-hljs"><pre><code class=3D"gmail-language-she=
ll gmail-hljs">[postgres] # select pg_walfile_name(&#39;76/7D000028&#39;);
     pg_walfile_name
--------------------------
 00000001000000760000007D
(1 row)</code></pre><pre><code class=3D"gmail-language-shell gmail-hljs"><b=
r></code></pre><pre><code class=3D"gmail-language-shell gmail-hljs">For det=
ails visit following link : <a href=3D"https://www.crunchydata.com/blog/pos=
tgres-wal-files-and-sequuence-numbers">https://www.crunchydata.com/blog/pos=
tgres-wal-files-and-sequuence-numbers</a></code></pre><pre><code class=3D"g=
mail-language-shell gmail-hljs"><br></code></pre><pre><code class=3D"gmail-=
language-shell gmail-hljs">Thanks</code></pre><pre><code class=3D"gmail-lan=
guage-shell gmail-hljs">Kashif Zeeshan</code></pre></code></pre></div><div>=
<br></div></div><br><div class=3D"gmail_quote gmail_quote_container"><div d=
ir=3D"ltr" class=3D"gmail_attr">On Tue, Apr 8, 2025 at 4:44=E2=80=AFPM Atul=
 Kumar &lt;<a href=3D"mailto:akumar14871@gmail.com">akumar14871@gmail.com</=
a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin:0p=
x 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><d=
iv dir=3D"auto">In streaming replication=C2=A0What is the way to check whic=
h &quot;WAL file&quot; is currently in use in primary=C2=A0 and in standby =
?<div dir=3D"auto"><br></div><div dir=3D"auto"><br></div><div dir=3D"auto">=
Regards.</div></div>
</blockquote></div>

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