Interesting paper. I only started reading / digesting it, but:
- I'm not sure how to interpret the Figure 1. It says "Flash writes (KB) per page", but it doesn't really say which page sizes were used. AFAIK MySQL has 16K by default, PostgreSQL has 8K, LeanStore has 4K, but that which makes the numbers a bit hard to compare.
- Likewise, I'm a bit unsure about the doublewrite buffering in Postgres, described as "indirect". Postgres doesn't really do doublewrite (we really should, I think), we write pages to WAL and then to data files. I assume that's what is meant by "indirect" in the paper. But this very much depends on the checkpoint frequency and write pattern, as the FPI is written only for the first page change. I wonder if the results in the paper consider this. Maybe the workload is such that it always hits the page just once between checkpoints (i.e. a worst case). Also, the WAL part is nicely sequential, which should play nice with SSDs.
- I'm not sure how to interpret the Figure 1. It says "Flash writes (KB) per page", but it doesn't really say which page sizes were used. AFAIK MySQL has 16K by default, PostgreSQL has 8K, LeanStore has 4K, but that which makes the numbers a bit hard to compare.
- Likewise, I'm a bit unsure about the doublewrite buffering in Postgres, described as "indirect". Postgres doesn't really do doublewrite (we really should, I think), we write pages to WAL and then to data files. I assume that's what is meant by "indirect" in the paper. But this very much depends on the checkpoint frequency and write pattern, as the FPI is written only for the first page change. I wonder if the results in the paper consider this. Maybe the workload is such that it always hits the page just once between checkpoints (i.e. a worst case). Also, the WAL part is nicely sequential, which should play nice with SSDs.