Re: [HACKERS] Restricting maximum keep segments by repslots

On 2020-Mar-31, Alvaro Herrera wrote:

> I'm not sure if I explained my proposal clearly.  What if
> XLogGetLastRemovedSegno returning zero means that every segment is
> valid?  We don't need to scan pg_xlog at all.

I mean this:

XLogSegNo
FindOldestXLogFileSegNo(void)
{
    XLogSegNo segno = XLogGetLastRemovedSegno();

    /* this is the only special case we need to care about */
    if (segno == 0)
        return some-value;

    return segno + 1;
}

... and that point one can further note that a freshly initdb'd system
(no file has been removed) has "1" as the first file.  So when segno is
0, you can return 1 and all should be well.  That means you can reduce
the function to this:

XLogSegNo
FindOldestXLogFileSegNo(void)
{
    return XLogGetLastRemovedSegno() + 1;
}


The tests still pass with this coding.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
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