On Fri, 24 Apr 2009, Rainer Gerhards wrote:
Another innocent question:
Let's say I used an exec() API exclusively. Now let me assume that I do, on
the *same* database connection, this calling sequence:
exec("begin transaction")
exec("insert ...")
exec("insert ...")
exec("insert ...")
exec("insert ...")
exec("insert ...")
exec("insert ...") [Point A]
exec("commit")
Is it safe to assume that this will result in a performance benefit (I know
that it causes more network traffic than necessary, but that's not my point -
I just talk of speedup). Will this performance speedup be considerable (along
the magnitude of 20 vs. 3 seconds for a given sequence?).
Yes, this speedup would be considerable
from the message at the bottom it would be on the order of
separate inserts, no transaction: 21.21s
separate inserts, same transaction: 1.89s
there is still another order of magnatude gain to be had by going to the
copy (and eliminating the extra round trips)
COPY (text): 0.10s
a copy looks something like
copy to table X from STDIN
data
data
data
Also, even more importantly, does this really many they are all in one
transaction?
yes.
In particular, what happens if the connection breaks at [Point
A], e.g. by the network connection going down for an extended period of time.
Is it safe to assume that then everything will be rolled back?
yes, every one of them would dissappear.
David Lang
Feedback is appreciated.
Rainer
-----Original Message-----
From: [email protected] [mailto:rsyslog-
[email protected]] On Behalf Of Rainer Gerhards
Sent: Thursday, April 23, 2009 4:38 PM
To: rsyslog-users
Subject: Re: [rsyslog] [PERFORM] performance for high-volume
loginsertion(fwd)
That's interesting. As a side-activity, I am thinking about a new
output
module interface. Especially given the discussion on the postgres list,
but
also some other thoughts about other modules (e.g. omtcp or the file
output),
I tend to use an approach that permits both string-based as well as
API-based
(API as in libpq) ways of doing things. I have not really designed
anything,
but the rough idea is that each plugin needs three entry points:
- start batch
- process single message
- end batch
Then, the plugin can decide itself what it wants to do and when. Most
importantly, this calling interface works well for string-based
transactions
as well as API-based ones.
For the output file writer, for example, I envision that over time it
will
have its own write buffer (for various reasons, for example I am also
discussing zipped writing with some folks). With this interface, I can
put
everything into the buffer, write out if needed but not if there is no
immediate need but I can make sure that I write out when the "end
batch"
entry point is called.
As I said, it is not really thought out yet, but maybe a starting
point. So
feedback is appreciated.
Rainer
-----Original Message-----
From: [email protected] [mailto:rsyslog-
[email protected]] On Behalf Of [email protected]
Sent: Wednesday, April 22, 2009 10:11 PM
To: rsyslog-users
Subject: Re: [rsyslog] [PERFORM] performance for high-volume log
insertion(fwd)
from the postgres performance mailing list, relative speeds of
different
ways of inserting data.
I've asked if the 'seperate inserts' mode is seperate round trips or
many
inserts in one round trip.
based on this it looks like prepared statements make a difference,
but
not
so much that other techniques (either a single statement or a copy)
aren't
comparable (or better) options.
David Lang
---------- Forwarded message ----------
Date: Wed, 22 Apr 2009 15:33:21 -0400
From: Glenn Maynard <[email protected]>
To: [email protected]
Subject: Re: [PERFORM] performance for high-volume log insertion
On Wed, Apr 22, 2009 at 8:19 AM, Stephen Frost <[email protected]>
wrote:
Yes, as I beleive was mentioned already, planning time for inserts
is
really small. Parsing time for inserts when there's little parsing
that
has to happen also isn't all *that* expensive and the same goes for
conversions from textual representations of data to binary.
We're starting to re-hash things, in my view. The low-hanging
fruit
is
doing multiple things in a single transaction, either by using
COPY,
multi-value INSERTs, or just multiple INSERTs in a single
transaction.
That's absolutely step one.
This is all well-known, covered information, but perhaps some numbers
will help drive this home. 40000 inserts into a single-column,
unindexed table; with predictable results:
separate inserts, no transaction: 21.21s
separate inserts, same transaction: 1.89s
40 inserts, 100 rows/insert: 0.18s
one 40000-value insert: 0.16s
40 prepared inserts, 100 rows/insert: 0.15s
COPY (text): 0.10s
COPY (binary): 0.10s
Of course, real workloads will change the weights, but this is more
or
less the magnitude of difference I always see--batch your inserts
into
single statements, and if that's not enough, skip to COPY.
--
Glenn Maynard
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