Re: [HACKERS] WIP aPatch: Pgbench Serialization and deadlock errors

> Hi Yugo,
>
> I tested with serialization error scenario by setting:
> default_transaction_isolation = 'repeatable read'
> The result was:
>
> $ pgbench -t 10 -c 10 --max-tries=10 test
> transaction type: <builtin: TPC-B (sort of)>
> scaling factor: 10
> query mode: simple
> number of clients: 10
> number of threads: 1
> maximum number of tries: 10
> number of transactions per client: 10
> number of transactions actually processed: 100/100
> number of failed transactions: 0 (0.000%)
> number of transactions retried: 35 (35.000%)
> total number of retries: 74
> latency average = 5.306 ms
> initial connection time = 15.575 ms
> tps = 1884.516810 (without initial connection time)
>
> I had hard time to understand what those numbers mean:
> number of transactions retried: 35 (35.000%)
> total number of retries: 74
>
> It seems "total number of retries" matches with the number of ERRORs
> reported in PostgreSQL. Good. What I am not sure is "number of
> transactions retried". What does this mean?

Oh, ok. I see it now. It turned out that "number of transactions
retried" does not actually means the number of transactions
rtried. Suppose pgbench exectutes following in a session:

BEGIN; -- transaction A starts
:
(ERROR)
ROLLBACK; -- transaction A aborts

(retry)

BEGIN; -- transaction B starts
:
(ERROR)
ROLLBACK; -- transaction B aborts

(retry)

BEGIN; -- transaction C starts
:
END; -- finally succeeds

In this case "total number of retries:" = 2 and "number of
transactions retried:" = 1. In this patch transactions A, B and C are
regarded as "same" transaction, so the retried transaction count
becomes 1. But it's confusing to use the language "transaction" here
because A, B and C are different transactions. I would think it's
better to use different language instead of "transaction", something
like "cycle"? i.e.

number of cycles retried: 35 (35.000%)

Best reagards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese:http://www.sraoss.co.jp