[slver]

It may be fast on its own, but I doubt it's faster than cursor+offset. Your idea is to materialize a slice starting from the cursor and offsetting within it. This means we still do offset, but without the cursor.

The thing is, the cursor is a lookup on an indexed sorted index, it's O(log N), it's effectively free already. And we add the cost of materializing the slice (if even just in memory), and introducing the potential of DoS-ing our server with this temporary state if we're not careful.

[inshadows]

I don't understand your point. I don't do any offset. I just pick 500 keys by cursor.

insert into temp select id, date from tbl where id >= c_id and date >= c_date order by date desc, id desc limit 500

I don't see doing any offset over the whole dataset.

> And we add the cost of materializing the slice (if even just in memory)

The alternative is to transfer 400 full rows of data that will be used just to compute pages.

> and introducing the potential of DoS-ing our server with this temporary state if we're not careful.

I don't see any DoS vector specific to this but I'd be thrilled to learn of one.

[slver]

> I don't understand your point. I don't do any offset. I just pick 500 keys by cursor

So you pick 500 keys and put them into a temp table. Then what? You still have to show a page that's 100 of those 500 keys.

> The alternative is to transfer 400 full rows of data that will be used just to compute pages.

The alternative is the hybrid cursor+offset approach, which doesn't transfer 400 full rows of anything.

> I don't see any DoS vector specific to this but I'd be thrilled to learn of one.

I generate enough sessions to fill your RAM with temp tables.

[inshadows]

> Then what? You still have to show a page that's 100 of those 500 keys.

I don't need to use offset. I can use limit. And also, offset in 500 rows dataset never was a problem.

> I generate enough sessions to fill your RAM with temp tables.

o_O These tables contain only keys. In your approach you're going to have 500 keys in memory as well. Moreover, I'm not wasting resources by transferring them in my application. I'm in fact saving resources. You're making things up.

EDIT: Are you arguing about performance impact of scanning 500 rows vs 100 rows (though I don't understand your approach either, you're skipping - scanning - 400 rows as well)? The problem of paging is scanning whole dataset.

[slver]

> EDIT: Are you arguing about performance impact of scanning 500 rows vs 100 rows (though I don't understand your approach either, you're skipping - scanning - 400 rows as well)? The problem of paging is scanning whole dataset.

Cursor+offset doesn't scan the whole dataset, and saving subsets in temp tables doesn't improve on it (i.e. temp tables make things slower). But I'm not sure where we misunderstand each other.

1. You start at the cursor.

2. You offset at most 400 records from the cursor.

3. You read 100 records.

The first point means you don't scan the whole dataset. The second point means for the next 5 pages you offset max 400 records. The third point means you read nothing, except what you want to display immediately.

[slver]

I wrote a longer reply, but it buried the lead.

So let's focus on the main issue I spotted:

> In your approach you're going to have 500 keys in memory as well.

That's not true at all. At no point I have 500 of anything in memory. So there's some big misunderstanding here about what I propose (and hence how it compares with your alternative).

If you want to go over my original comments again and ask questions to understand the concept, I'm at your service.