> On Dec 3, 2021, at 5:39 PM, Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> On Fri, Dec 03, 2021 at 10:07:19PM +0000, Chuck Lever III wrote:
>>
>>
>>>> On Dec 3, 2021, at 4:55 PM, Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>>>
>>> From: "J. Bruce Fields" <bfields@xxxxxxxxxx>
>>>
>>> Currently nfsdcld is doing three fdatasyncs for each upcall. Based on
>>> SQLite documentation, WAL mode should also be safe, and I can confirm
>>> from an strace that it results in only one fdatasync each.
>>>
>>> This may be a bottleneck e.g. when lots of clients are being created or
>>> expired at once (e.g. on reboot).
>>>
>>> Not bothering with error checking, as this is just an optimization and
>>> nfsdcld will still function without. (Might be better to log something
>>> on failure, though.)
>>
>> I'm in full philosophical agreement for performance improvements
>> in this area. There are some caveats for WAL:
>>
>> - It requires SQLite v3.7.0 (2010). configure.ac may need to be
>> updated.
>
> Makes sense. But I dug around a bit, and how to do this is a total
> mystery to me....
aclocal/libsqlite3.m4 has an SQLITE_VERSION_NUMBER check.
>> - All processes using the DB file have to be on the same system.
>> Not sure if this matters for some DR scenarios that nfs-utils
>> is supposed to support.
>
> I don't think we support that.
>
>> - WAL mode is persistent; you could set this at database creation
>> time and it should be sti cky.
>
> I wanted to upgrade existing databases too, and figured there's no harm
> in calling it on each startup.
Ah. Makes sense!
>> - Documentation says "synchronous = FULL is the most commonly
>> used synchronous setting when not in WAL mode." Why are both
>> PRAGMAs necessary here?
>
> Maybe they're not; I think I did see that FULL is actually the default
> but I can't find that in the documentation right now.
>
> --b.
>
>>
>> I agree that nfsdcld functionality is not affected if the first
>> PRAGMA fails.
>>
>>
>>> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
>>> ---
>>> utils/nfsdcld/sqlite.c | 3 +++
>>> 1 file changed, 3 insertions(+)
>>>
>>> diff --git a/utils/nfsdcld/sqlite.c b/utils/nfsdcld/sqlite.c
>>> index 03016fb95823..b248eeffa204 100644
>>> --- a/utils/nfsdcld/sqlite.c
>>> +++ b/utils/nfsdcld/sqlite.c
>>> @@ -826,6 +826,9 @@ sqlite_prepare_dbh(const char *topdir)
>>> goto out_close;
>>> }
>>>
>>> + sqlite3_exec(dbh, "PRAGMA journal_mode = WAL;", NULL, NULL, NULL);
>>> + sqlite3_exec(dbh, "PRAGMA synchronous = FULL;", NULL, NULL, NULL);
>>> +
>>> ret = sqlite_query_schema_version();
>>> switch (ret) {
>>> case CLD_SQLITE_LATEST_SCHEMA_VERSION:
>>> --
>>> 2.33.1
>>>
>>
>> --
>> Chuck Lever
>>
>>
