Thanks Gunter. Below are the execution times:
pragma table_value(pragma table_info(adas_link_geometry) 2mspragma
table_value(pragma table_info(idx_adas_link_geometry) 1msSELECT <my statement
#1> 1.1 secondsSELECT <my statement #1> 9msSELECT <my statement #1> 9msSELECT
<my statement #2 with slightly different search values> 9msSELECT <my statement
#3 with slightly different search values> 9ms
It appears that the bulk of the time is taken up in the initial query.
Presumably, there is buffering that occurs both in SQLite and my file system to
assist in future queries. I've changed some buffer parameters in my file
system initialization and was able to reduce the initial query time from 1.6
seconds to 1.1 seconds. I've also asked Segger file system tech support for
some help understanding the initial query time as it applies to file
reads/buffering. Using sqlite3_config() I've changed some SQLite page cache
and heap parameters, and disabled a few unwanted #defines which has decreased
initial query time. Do the above times give you any clues about the initial
query time? Any other ideas would be helpful.
Thanks again.
From: Hick Gunter <[email protected]>
To: 'SQLite mailing list' <[email protected]>
Sent: Wednesday, March 21, 2018 1:29 AM
Subject: Re: [sqlite] [EXTERNAL] R*Trees query data cached?
The .describe is just to make sure the SQLite has loaded the table definition.
Try pragma table_info(<table_name>);
-----Ursprüngliche Nachricht-----
Von: sqlite-users [mailto:[email protected]] Im
Auftrag von David Ashman - Zone 7 Engineering, LLC
Gesendet: Dienstag, 20. März 2018 22:45
An: SQLite mailing list <[email protected]>
Betreff: Re: [sqlite] [EXTERNAL] R*Trees query data cached?
Thank you for the quick reply Hick. I've implemented your script file in C
since I'm running this application in the embedded world with no OS. I don't
see a .describe in the SQLite documentation. I've tried to use .schema but
that returns an error. Do you have another suggestion to obtain the table
information you had in mind?
From: Hick Gunter <[email protected]>
To: 'SQLite mailing list' <[email protected]>
Sent: Tuesday, March 20, 2018 9:04 AM
Subject: Re: [sqlite] [EXTERNAL] R*Trees query data cached?
SQLite does not have "query caching". It does have a "page cache" that will
keep heavily used pages iin memory. There is also the possibility of a
file-system/os-level cache. To break down the 1.6 seconds required for the
first query, try executing an sql script. In linux this would be along the
lines of:
> date; sqlite3 file.db < script.sql;date
With script.sql containing:
Select strftime('%Y-%m-%d %H:%M:%S.%f'); Select strftime('%Y-%m-%d
%H:%M:%S.%f'); .describe adas_link_geometry Select strftime('%Y-%m-%d
%H:%M:%S.%f'); .describe idx_adas_link_geometry Select strftime('%Y-%m-%d
%H:%M:%S.%f'); Select <your statement>; Select strftime('%Y-%m-%d
%H:%M:%S.%f'); Select <your statement>; Select strftime('%Y-%m-%d
%H:%M:%S.%f'); Select <your statement>; Select strftime('%Y-%m-%d %H:%M:%S.%f');
This should give you an idea of where the time is being spent.
-----Ursprüngliche Nachricht-----
Von: sqlite-users [mailto:[email protected]] Im
Auftrag von David Ashman - Zone 7 Engineering, LLC
Gesendet: Dienstag, 20. März 2018 16:34
An: [email protected]
Betreff: [EXTERNAL] [sqlite] R*Trees query data cached?
Hello -
I have a question on SQLite query data buffering.
I'm successfully using SQLite v3.22.0 on an embedded ARM processor from ST with
SD card. The database file size is about 750MB. The file system is Segger
emFile FAT32. I've configured SQLite to use 6MB RAM for heap. I've done some
query time benchmarking and found that the very first R*Trees query takes about
1.6 seconds to complete. Each successive R*Trees query (same query string with
slightly different search parameters) takes about 11ms to complete. Being new
to SQLite and spatial queries, I'm trying to understand the substantial query
time differences... does SQLite cache data from each query for future queries?
The initial query:SELECT LINK_ID, FROM_REF_ELEVATION, TO_REF_ELEVATION FROM
adas_link_geometry, idx_adas_link_geometry WHERE adas_link_geometry.ROWID =
idx_adas_link_geometry.id AND minLat > 454760320 AND maxLat < 454800320 AND
minLong > -1226807072 AND maxLong < -1226767072;
Thanks in advance,Dave
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Klitschgasse 2-4, A-1130 Vienna | FN 157284 a, HG Wien, DVR: 0430013 | (O) +43
1 80100 - 0
May be privileged. May be confidential. Please delete if not the addressee.
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