ConETS table consistency while entries are deleted from 2 processes

[Frank Muller]

Crystal clear Jesper, thanks.

is purge1/1 valid/correct?

/Frank

On Sun, Dec 8, 2019 at 9:29 AM Frank Muller <frank.muller.erl@REDACTED>
> wrote:
>
>> Hi all
>>
>>
>> Lets assume a public ETS table of type ‘ordered_set’.
>>
>>
> The ETS documentation defines "safe traversal". Traversal of `ordered_set`
> tables are always safe. That is, they will do the "right thing" if updates
> are done while traversal happens.
>
> For tables of the other types, you either do the whole traversal in one
> call, or you use the safe_fixtable/2 call to fix the table while traversal
> is happening.
>
> The underlying reason is that the table has an order. This means we can
> always drill down into the table and find the place we "were" so to speak
> by utilizing this order. In the case of e.g., `set` tables, we don't a
> priori have an order, so we are encoding something like a hash bucket and
> the element we reached. But if that element is gone, we don't know where we
> were, and there is no other structural information to go by. The fixtable
> calls basically postpones changes to the table in a separate buffer until
> the traversal is done, then replays the buffer on the table. This ensures
> the core table is traversal-stable. Requests to the table first checks the
> buffer before checking the main core table[0]
>
> [0] This model is essentially a 2 level log-structured-merge-tree (LSM
> tree) variant.
>
> --
> J.
>
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