Re: zheap: a new storage format for PostgreSQL

Hello Amit,

> At EnterpriseDB, we (me and some of my colleagues) are working from more
> than a year on the new storage format in which only the latest version of
> the data is kept in main storage and the old versions are moved to an undo
> log.  [...]

This looks more than great!

> *We’ve shown the performance improvement of zheap over heap in a few
> different pgbench scenarios. [...]

> 2. Transaction aborts will be expensive.

ISTM that some scenarii should also test the performance impact when the 
zheap storage is expected to be worse than the heap storage, i.e. with 
some rollback which will exercise the undo stuff. There does not seem to 
be any in your report, I apologise if I misread it.

I would suggest that you can use pgbench scripts such as:

   -- commit.sql
   \set aid random(1, 100000 * :scale)
   BEGIN;
   UPDATE pgbench_accounts
     SET abalance = abalance + 1
     WHERE aid = :aid;
   COMMIT;

and

   -- rollback.sql
   \set aid random(1, 100000 * :scale)
   BEGIN;
   UPDATE pgbench_accounts
     SET abalance = abalance + 1
     WHERE aid = :aid;
   ROLLBACK;

that can run with various weights to change how much rollback is injected,
eg 1% rollback rate is achieved with:

   pgbench -T 10 -P 1 -M prepared -r \
     -f SQL/commit.sql@99 -f SQL/rollback.sql@1

Also, I would be wary of doing only max speed test, and consider more 
realistic --rate tests where the tps is fixed.

-- 
Fabien.