Thread: Re: VACUUM degrades performance significantly. Database
If you are always looking for exact matches, I would suggest experimenting with a hashed index. The character fields of your index are very long, and it may be beneficial to try hashing as an alternative. Of course, if you need to do greater than, less than, between sorts of queries, the hashed index simply won't work. > -----Original Message----- > From: Stephen [mailto:jleelim@xxxxxx.com] > Sent: Wednesday, October 15, 2003 12:27 PM > To: pgsql-general@postgresql.org > Subject: Re: [GENERAL] VACUUM degrades performance > significantly. Database > > > Scott, > > I dropped the 5 way unique index and the VACUUM improved > slightly. I ran VACUUM, ANALYZE, VACUUM and queries > repeatedly. The max response time seem to have reduced to > 1700 msec from 2300 msec. The higher load and vmstat during > VACUUM remained the same. It's still not enough to justify > dropping the index for my purposes. > > tsdb=# explain analyze select * from table1 where id = > '3305b141837f065d673aa09cf382d331'; > > QUERY PLAN > -------------------------------------------------------------- > -------------- > -------------------------------------------------------- > Index Scan using table1_pkey on table1 (cost=0.00..6.01 > rows=1 width=346) (actual time=1762.34..1762.37 rows=1 loops=1) > Index Cond: (id = > '3305b141837f065d673aa09cf382d331'::character varying) Total > runtime: 1762.50 msec (3 rows) > > Regards, > > Stephen > > ""scott.marlowe"" <scott.marlowe@ihs.com> wrote in message > news:Pine.LNX.4.33.0310151150580.23393-100000@css120.ihs.com... > > It sounds like you might be I/O bound. if you drop the 5 > way unique > > index for a test, how do the vacuum and parallel select run? > > > > On Wed, 15 Oct 2003, Stephen wrote: > > > > > Hello, > > > > > > Is it normal for plain VACUUM on large table to degrade > performance > > > by > over > > > 9 times? My database becomes unusable when VACUUM runs. > From reading > > > newsgroups, I thought VACUUM should only slow down by 10% to 15%. > > > Other > MVCC > > > databases like MySQL InnoDB can even VACUUM discretely (runs > internally). Is > > > it my Linux system or is it PostgreSQL? > > > > > > The database is mostly read-only. There are 133,000 rows and each > > > row is about 2.5kB in size (mostly due to the bytea > column holding a > > > binary > image). > > > The long row causes system to TOAST the table. VACUUM > takes 5m20s to > > > complete. I repeatedly ran the following tests while system is > > > idling: > > > > > > > > > In normal operation: > > > ==================== > > > tsdb=# explain analyze select * from table1 where id = > > > '33a4e9b6eae09634f4ff3e6fa9280f6e'; > > > QUERY > > > PLAN > > > > > ---------------------------------------------------------------------- > > ---- > -- > > > ---------------------------------------------------- > > > Index Scan using table1_pkey on table1 (cost=0.00..6.01 rows=1 > width=346) > > > (actual time=25.30..25.31 rows=1 loops=1) > > > Index Cond: (id = '33a4e9b6eae09634f4ff3e6fa9280f6e'::character > varying) > > > Total runtime: 25.52 msec > > > (3 rows) > > > > > > When VACUUM runs: > > > ================= > > > tsdb=# explain analyze select * from table1 where id = > > > '336139b47b7faf09fc4d4f03680a4ce5'; > > > > QUERY > > > PLAN > > > > > ---------------------------------------------------------------------- > > ---- > -- > > > -------------------------------------------------------- > > > Index Scan using table1_pkey on table1 (cost=0.00..6.01 rows=1 > width=346) > > > (actual time=2290.07..2290.10 rows=1 loops=1) > > > Index Cond: (id = '336139b47b7faf09fc4d4f03680a4ce5'::character > varying) > > > Total runtime: 2290.22 msec > > > (3 rows) > > > > > > > > > VACUUM output: > > > ============== > > > tsdb=# VACUUM VERBOSE table1; > > > INFO: --Relation public.table1-- > > > INFO: Pages 5887: Changed 0, Empty 0; Tup 132672: Vac 0, Keep 0, > > > UnUsed 144. > > > Total CPU 0.28s/0.01u sec elapsed 36.08 sec. > > > INFO: --Relation pg_toast.pg_toast_12437088-- > > > INFO: Pages 40495: Changed 0, Empty 0; Tup 197587: Vac 0, Keep 0, > UnUsed > > > 235. > > > Total CPU 1.73s/0.20u sec elapsed 233.91 sec. VACUUM > > > > > > > > > > > > vmstat while VACUUM'ing: > > > ======================== > > > procs memory swap > io system > > > cpu > > > r b w swpd free buff cache si so bi > bo in cs us > sy > > > id > > > 0 1 1 74420 6520 30616 405128 0 0 1280 > 0 287 487 0 > 1 > > > 99 > > > 0 1 0 74420 6520 30620 405168 0 0 1196 > 0 271 436 0 > 0 > > > 100 > > > 0 1 1 74420 6520 30620 405120 0 0 1496 > 4 289 491 0 > 3 > > > 97 > > > 0 1 1 74420 6520 30620 405208 0 0 1280 > 0 268 466 0 > 0 > > > 100 > > > 1 0 1 74420 6520 30620 405208 0 0 1280 > 0 288 482 0 > 1 > > > 99 > > > 1 0 1 74420 6520 30632 405200 0 0 1416 > 8 277 441 1 > 2 > > > 97 > > > 3 1 1 74416 6520 30632 405196 4 0 1284 > 0 284 473 0 > 3 > > > 97 > > > > > > > > > > > > PostgreSQL configuration (the only changes made): > > > ================================================= > > > max_connections = 1024 > > > shared_buffers = 2800 > > > sort_mem = 8192 > > > vacuum_mem = 8192 > > > effective_cache_size = 32000 > > > > > > > > > System: > > > ======= > > > Hardware: AMD 1.2GHz Athlon 512MB SDRAM > > > OS: Redhat Linux 9.0 (kernel 2.4.20-8) > > > FS: EXT3 with Journalling mounted with noatime, UDMA5 > > > Disk1 (Linux): IDE 20GB 7200 RPM Western Digital > > > Disk2 (PostgreSQL): IDE 120GB 7200 RPM Western Digital > > > PostgreSQL: 7.3.4 > > > > > > > > > hdparm: > > > ======= > > > /dev/hda: (Linux partition) > > > multcount = 16 (on) > > > IO_support = 1 (32-bit) > > > unmaskirq = 1 (on) > > > using_dma = 1 (on) > > > keepsettings = 0 (off) > > > readonly = 0 (off) > > > readahead = 8 (on) > > > geometry = 2498/255/63, sectors = 40132503, start = 0 > > > > > > /dev/hdc: (PostgreSQL partition) > > > multcount = 16 (on) > > > IO_support = 1 (32-bit) > > > unmaskirq = 1 (on) > > > using_dma = 1 (on) > > > keepsettings = 1 (on) > > > readonly = 0 (off) > > > readahead = 8 (on) > > > geometry = 232581/16/63, sectors = 234441648, start = 0 > > > > > > > > > Schema: > > > ======= > > > CREATE TABLE table1 ( > > > id varchar(32) DEFAULT '' > NOT > NULL, > > > colname1 varchar(10) DEFAULT 'http' > NOT > > > NULL, > > > colname2 varchar(300) DEFAULT '' > NOT > NULL, > > > colname3 varchar(5) DEFAULT '' > NOT > > > NULL, > > > colname4 varchar(300) DEFAULT '' > NOT > > > NULL, > > > colname5 varchar(300) DEFAULT '' > NOT > NULL, > > > colname6 integer DEFAULT 0 > NOT > > > NULL, > > > colname7 integer DEFAULT 0 > NOT > > > NULL, > > > colname8 integer DEFAULT 200 > NOT > NULL, > > > colname9 varchar(10) DEFAULT '' > NOT > > > NULL, > > > colname10 varchar(10) DEFAULT '' > NOT > NULL, > > > colname11 varchar(100) DEFAULT '' > NOT > > > NULL, > > > colname12 varchar(100) DEFAULT '' > NOT > NULL, > > > colname13 varchar(100) DEFAULT '' > NOT > NULL, > > > colname14 varchar(20) DEFAULT '' > NOT NULL, > > > colname15 integer DEFAULT 640 > NOT > > > NULL, > > > colname16 integer DEFAULT 480 > NOT > > > NULL, > > > colname17 integer DEFAULT 120 > NOT > > > NULL, > > > colname18 integer DEFAULT 90 > NOT > > > NULL, > > > colname19 timestamp DEFAULT > CURRENT_TIMESTAMP NOT > > > NULL, > > > colname20 timestamp DEFAULT > CURRENT_TIMESTAMP NOT > > > NULL, > > > colname21 integer DEFAULT 0 > NOT NULL, > > > colname22 integer DEFAULT 0 > NOT > NULL, > > > colname23 timestamp DEFAULT CURRENT_TIMESTAMP > NOT NULL, > > > colname24 integer DEFAULT 0 > NOT > > > NULL, > > > colname25 integer DEFAULT 0 > NOT > NULL, > > > colname26 varchar(10) DEFAULT '' > NOT > > > NULL, > > > colname28 varchar(10) DEFAULT '' > NOT NULL, > > > colname29 varchar(10) DEFAULT 'jpeg' > NOT > > > NULL, > > > colname30 varchar(20) DEFAULT '' > NOT NULL, > > > colname31 bytea > , > > > PRIMARY KEY (id) > > > ) WITHOUT OIDS > > > > > > CREATE UNIQUE INDEX table1_idx_1 ON table1 (colname1, colname2, > colname3, > > > colname4, colname5) > > > > > > Sigh, :-( > > > > > > Stephen > > > > > > > > > > > > > > > ---------------------------(end of > broadcast)--------------------------- > > > TIP 6: Have you searched our list archives? > > > > > > http://archives.postgresql.org > > > > > > > > > ---------------------------(end of > broadcast)--------------------------- > > TIP 4: Don't 'kill -9' the postmaster > > > > > > ---------------------------(end of > broadcast)--------------------------- > TIP 9: the planner will ignore your desire to choose an index > scan if your > joining column's datatypes do not match >
Dann, I already hashed the 5-way index under the column "id". Removing the 5-way index didn't improve responsiveness, but setting elvtune on Linux did! The 5-way index is still needed for my purposes. Thanks anyway. Stephen :-) ""Dann Corbit"" <DCorbit@connx.com> wrote in message news:D90A5A6C612A39408103E6ECDD77B8294CE21E@voyager.corporate.connx.com... > If you are always looking for exact matches, I would suggest > experimenting with a hashed index. > > The character fields of your index are very long, and it may be > beneficial to try hashing as an alternative. > > Of course, if you need to do greater than, less than, between sorts of > queries, the hashed index simply won't work. > > > -----Original Message----- > > From: Stephen [mailto:jleelim@xxxxxx.com] > > Sent: Wednesday, October 15, 2003 12:27 PM > > To: pgsql-general@postgresql.org > > Subject: Re: [GENERAL] VACUUM degrades performance > > significantly. Database > > > > > > Scott, > > > > I dropped the 5 way unique index and the VACUUM improved > > slightly. I ran VACUUM, ANALYZE, VACUUM and queries > > repeatedly. The max response time seem to have reduced to > > 1700 msec from 2300 msec. The higher load and vmstat during > > VACUUM remained the same. It's still not enough to justify > > dropping the index for my purposes. > > > > tsdb=# explain analyze select * from table1 where id = > > '3305b141837f065d673aa09cf382d331'; > > > > QUERY PLAN > > -------------------------------------------------------------- > > -------------- > > -------------------------------------------------------- > > Index Scan using table1_pkey on table1 (cost=0.00..6.01 > > rows=1 width=346) (actual time=1762.34..1762.37 rows=1 loops=1) > > Index Cond: (id = > > '3305b141837f065d673aa09cf382d331'::character varying) Total > > runtime: 1762.50 msec (3 rows) > > > > Regards, > > > > Stephen > > > > ""scott.marlowe"" <scott.marlowe@ihs.com> wrote in message > > news:Pine.LNX.4.33.0310151150580.23393-100000@css120.ihs.com... > > > It sounds like you might be I/O bound. if you drop the 5 > > way unique > > > index for a test, how do the vacuum and parallel select run? > > > > > > On Wed, 15 Oct 2003, Stephen wrote: > > > > > > > Hello, > > > > > > > > Is it normal for plain VACUUM on large table to degrade > > performance > > > > by > > over > > > > 9 times? My database becomes unusable when VACUUM runs. > > From reading > > > > newsgroups, I thought VACUUM should only slow down by 10% to 15%. > > > > Other > > MVCC > > > > databases like MySQL InnoDB can even VACUUM discretely (runs > > internally). Is > > > > it my Linux system or is it PostgreSQL? > > > > > > > > The database is mostly read-only. There are 133,000 rows and each > > > > row is about 2.5kB in size (mostly due to the bytea > > column holding a > > > > binary > > image). > > > > The long row causes system to TOAST the table. VACUUM > > takes 5m20s to > > > > complete. I repeatedly ran the following tests while system is > > > > idling: > > > > > > > > > > > > In normal operation: > > > > ==================== > > > > tsdb=# explain analyze select * from table1 where id = > > > > '33a4e9b6eae09634f4ff3e6fa9280f6e'; > > > > QUERY > > > > PLAN > > > > > > > > ---------------------------------------------------------------------- > > > ---- > > -- > > > > ---------------------------------------------------- > > > > Index Scan using table1_pkey on table1 (cost=0.00..6.01 rows=1 > > width=346) > > > > (actual time=25.30..25.31 rows=1 loops=1) > > > > Index Cond: (id = '33a4e9b6eae09634f4ff3e6fa9280f6e'::character > > varying) > > > > Total runtime: 25.52 msec > > > > (3 rows) > > > > > > > > When VACUUM runs: > > > > ================= > > > > tsdb=# explain analyze select * from table1 where id = > > > > '336139b47b7faf09fc4d4f03680a4ce5'; > > > > > > QUERY > > > > PLAN > > > > > > > > ---------------------------------------------------------------------- > > > ---- > > -- > > > > -------------------------------------------------------- > > > > Index Scan using table1_pkey on table1 (cost=0.00..6.01 rows=1 > > width=346) > > > > (actual time=2290.07..2290.10 rows=1 loops=1) > > > > Index Cond: (id = '336139b47b7faf09fc4d4f03680a4ce5'::character > > varying) > > > > Total runtime: 2290.22 msec > > > > (3 rows) > > > > > > > > > > > > VACUUM output: > > > > ============== > > > > tsdb=# VACUUM VERBOSE table1; > > > > INFO: --Relation public.table1-- > > > > INFO: Pages 5887: Changed 0, Empty 0; Tup 132672: Vac 0, Keep 0, > > > > UnUsed 144. > > > > Total CPU 0.28s/0.01u sec elapsed 36.08 sec. > > > > INFO: --Relation pg_toast.pg_toast_12437088-- > > > > INFO: Pages 40495: Changed 0, Empty 0; Tup 197587: Vac 0, Keep 0, > > UnUsed > > > > 235. > > > > Total CPU 1.73s/0.20u sec elapsed 233.91 sec. VACUUM > > > > > > > > > > > > > > > > vmstat while VACUUM'ing: > > > > ======================== > > > > procs memory swap > > io system > > > > cpu > > > > r b w swpd free buff cache si so bi > > bo in cs us > > sy > > > > id > > > > 0 1 1 74420 6520 30616 405128 0 0 1280 > > 0 287 487 0 > > 1 > > > > 99 > > > > 0 1 0 74420 6520 30620 405168 0 0 1196 > > 0 271 436 0 > > 0 > > > > 100 > > > > 0 1 1 74420 6520 30620 405120 0 0 1496 > > 4 289 491 0 > > 3 > > > > 97 > > > > 0 1 1 74420 6520 30620 405208 0 0 1280 > > 0 268 466 0 > > 0 > > > > 100 > > > > 1 0 1 74420 6520 30620 405208 0 0 1280 > > 0 288 482 0 > > 1 > > > > 99 > > > > 1 0 1 74420 6520 30632 405200 0 0 1416 > > 8 277 441 1 > > 2 > > > > 97 > > > > 3 1 1 74416 6520 30632 405196 4 0 1284 > > 0 284 473 0 > > 3 > > > > 97 > > > > > > > > > > > > > > > > PostgreSQL configuration (the only changes made): > > > > ================================================= > > > > max_connections = 1024 > > > > shared_buffers = 2800 > > > > sort_mem = 8192 > > > > vacuum_mem = 8192 > > > > effective_cache_size = 32000 > > > > > > > > > > > > System: > > > > ======= > > > > Hardware: AMD 1.2GHz Athlon 512MB SDRAM > > > > OS: Redhat Linux 9.0 (kernel 2.4.20-8) > > > > FS: EXT3 with Journalling mounted with noatime, UDMA5 > > > > Disk1 (Linux): IDE 20GB 7200 RPM Western Digital > > > > Disk2 (PostgreSQL): IDE 120GB 7200 RPM Western Digital > > > > PostgreSQL: 7.3.4 > > > > > > > > > > > > hdparm: > > > > ======= > > > > /dev/hda: (Linux partition) > > > > multcount = 16 (on) > > > > IO_support = 1 (32-bit) > > > > unmaskirq = 1 (on) > > > > using_dma = 1 (on) > > > > keepsettings = 0 (off) > > > > readonly = 0 (off) > > > > readahead = 8 (on) > > > > geometry = 2498/255/63, sectors = 40132503, start = 0 > > > > > > > > /dev/hdc: (PostgreSQL partition) > > > > multcount = 16 (on) > > > > IO_support = 1 (32-bit) > > > > unmaskirq = 1 (on) > > > > using_dma = 1 (on) > > > > keepsettings = 1 (on) > > > > readonly = 0 (off) > > > > readahead = 8 (on) > > > > geometry = 232581/16/63, sectors = 234441648, start = 0 > > > > > > > > > > > > Schema: > > > > ======= > > > > CREATE TABLE table1 ( > > > > id varchar(32) DEFAULT '' > > NOT > > NULL, > > > > colname1 varchar(10) DEFAULT 'http' > > NOT > > > > NULL, > > > > colname2 varchar(300) DEFAULT '' > > NOT > > NULL, > > > > colname3 varchar(5) DEFAULT '' > > NOT > > > > NULL, > > > > colname4 varchar(300) DEFAULT '' > > NOT > > > > NULL, > > > > colname5 varchar(300) DEFAULT '' > > NOT > > NULL, > > > > colname6 integer DEFAULT 0 > > NOT > > > > NULL, > > > > colname7 integer DEFAULT 0 > > NOT > > > > NULL, > > > > colname8 integer DEFAULT 200 > > NOT > > NULL, > > > > colname9 varchar(10) DEFAULT '' > > NOT > > > > NULL, > > > > colname10 varchar(10) DEFAULT '' > > NOT > > NULL, > > > > colname11 varchar(100) DEFAULT '' > > NOT > > > > NULL, > > > > colname12 varchar(100) DEFAULT '' > > NOT > > NULL, > > > > colname13 varchar(100) DEFAULT '' > > NOT > > NULL, > > > > colname14 varchar(20) DEFAULT '' > > NOT NULL, > > > > colname15 integer DEFAULT 640 > > NOT > > > > NULL, > > > > colname16 integer DEFAULT 480 > > NOT > > > > NULL, > > > > colname17 integer DEFAULT 120 > > NOT > > > > NULL, > > > > colname18 integer DEFAULT 90 > > NOT > > > > NULL, > > > > colname19 timestamp DEFAULT > > CURRENT_TIMESTAMP NOT > > > > NULL, > > > > colname20 timestamp DEFAULT > > CURRENT_TIMESTAMP NOT > > > > NULL, > > > > colname21 integer DEFAULT 0 > > NOT NULL, > > > > colname22 integer DEFAULT 0 > > NOT > > NULL, > > > > colname23 timestamp DEFAULT CURRENT_TIMESTAMP > > NOT NULL, > > > > colname24 integer DEFAULT 0 > > NOT > > > > NULL, > > > > colname25 integer DEFAULT 0 > > NOT > > NULL, > > > > colname26 varchar(10) DEFAULT '' > > NOT > > > > NULL, > > > > colname28 varchar(10) DEFAULT '' > > NOT NULL, > > > > colname29 varchar(10) DEFAULT 'jpeg' > > NOT > > > > NULL, > > > > colname30 varchar(20) DEFAULT '' > > NOT NULL, > > > > colname31 bytea > > , > > > > PRIMARY KEY (id) > > > > ) WITHOUT OIDS > > > > > > > > CREATE UNIQUE INDEX table1_idx_1 ON table1 (colname1, colname2, > > colname3, > > > > colname4, colname5) > > > > > > > > Sigh, :-( > > > > > > > > Stephen > > > > > > > > > > > > > > > > > > > > ---------------------------(end of > > broadcast)--------------------------- > > > > TIP 6: Have you searched our list archives? > > > > > > > > http://archives.postgresql.org > > > > > > > > > > > > > ---------------------------(end of > > broadcast)--------------------------- > > > TIP 4: Don't 'kill -9' the postmaster > > > > > > > > > > > ---------------------------(end of > > broadcast)--------------------------- > > TIP 9: the planner will ignore your desire to choose an index > > scan if your > > joining column's datatypes do not match > > > > ---------------------------(end of broadcast)--------------------------- > TIP 6: Have you searched our list archives? > > http://archives.postgresql.org >
"Stephen" <jleelim@xxxxxx.com> writes: > ""Dann Corbit"" <DCorbit@connx.com> wrote in message > news:D90A5A6C612A39408103E6ECDD77B8294CE21E@voyager.corporate.connx.com... > > If you are always looking for exact matches, I would suggest > > experimenting with a hashed index. > > I already hashed the 5-way index under the column "id". Removing the 5-way > index didn't improve responsiveness, but setting elvtune on Linux did! The > 5-way index is still needed for my purposes. He meant to use a "hash index" which is a type of index you can create in postgres. However you should realize that hash indexes have some major bugs in 7.3 and prior. Even in 7.4 with a lot of bugs fixed they still have a lot of limitations that make them probably not such a hot idea. -- greg
Stephen wrote:
> Good news,
>
> I partially fixed the problem on Linux 2.4. It appears the responsiveness
> can be improved significantly by tuning the disk IO elevator in Linux using
> "elvtune" in util-linux. The elevator in Linux is used to re-order
> read/write requests to reduce disk seeks by ordering requests according to
> disk sectors. Unfortunately, the elevator in kernel 2.4 is not very smart
> (or flexible I should say depending on your needs) and can starve a
> read/write request for a long time if not properly tuned.
> elvtune -r 2048 -w 8192 /dev/hdc (default Redhat 9):
> ====================================================
Are you sure ? In my RH9.0 installation I obtain:
# elvtune /dev/sda7
/dev/sda7 elevator ID 5
read_latency: 64
write_latency: 8192
max_bomb_segments: 6
may be your problem is due the fact that someone change these values
on your machine!
Regards
Gaetano Mendola
On Sun, 19 Oct 2003 22:02:11 +0200
Gaetano Mendola <mendola@bigfoot.com> wrote:
> Are you sure ? In my RH9.0 installation I obtain:
>
> # elvtune /dev/sda7
>
> /dev/sda7 elevator ID 5
> read_latency: 64
> write_latency: 8192
> max_bomb_segments: 6
>
>
The default on RH8 is:
/dev/hda1 elevator ID 0
read_latency: 2048
write_latency: 8192
max_bomb_segments: 0
which match his values. I'm quite interested in this and I'm going to
try playing with it later today...
--
Jeff Trout <jeff@jefftrout.com>
http://www.jefftrout.com/
http://www.stuarthamm.net/
Nope, I installed the RedHat 9 myself and no one else has access to this machine. It's either that Redhat uses a different elevator setting for SCSI drives than IDEs or the latest Redhat updates I applied brought it to my current numbers. Besides, I believe your values may indicate an outdated system because IIRC the max_bomb_segments has been disabled and should always be zero because of some inefficiencies in the elevator algorithm. Regards, Stephen "Gaetano Mendola" <mendola@bigfoot.com> wrote in message news:3F92EDC3.5010602@bigfoot.com... > Stephen wrote: > > > Good news, > > > > I partially fixed the problem on Linux 2.4. It appears the responsiveness > > can be improved significantly by tuning the disk IO elevator in Linux using > > "elvtune" in util-linux. The elevator in Linux is used to re-order > > read/write requests to reduce disk seeks by ordering requests according to > > disk sectors. Unfortunately, the elevator in kernel 2.4 is not very smart > > (or flexible I should say depending on your needs) and can starve a > > read/write request for a long time if not properly tuned. > > elvtune -r 2048 -w 8192 /dev/hdc (default Redhat 9): > > ==================================================== > > Are you sure ? In my RH9.0 installation I obtain: > > # elvtune /dev/sda7 > > /dev/sda7 elevator ID 5 > read_latency: 64 > write_latency: 8192 > max_bomb_segments: 6 > > > may be your problem is due the fact that someone change these values > on your machine! > > > > Regards > Gaetano Mendola > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: the planner will ignore your desire to choose an index scan if your > joining column's datatypes do not match >
Stephen wrote:
> Nope, I installed the RedHat 9 myself and no one else has access to this
> machine. It's either that Redhat uses a different elevator setting for SCSI
> drives than IDEs or the latest Redhat updates I applied brought it to my
> current numbers. Besides, I believe your values may indicate an outdated
> system because IIRC the max_bomb_segments has been disabled and should
> always be zero because of some inefficiencies in the elevator algorithm.
>
> Regards, Stephen
Well, I obtains the same values for two different RH9 installation:
# uname -a
Linux XXXX 2.4.20-13.9smp #1 SMP Mon May 12 10:48:05 EDT 2003 i686 i686
i386 GNU/Linux
# elvtune /dev/hda6
/dev/hda6 elevator ID 1
read_latency: 64
write_latency: 8192
max_bomb_segments: 6
# uname -a
Linux XXXX 2.4.20-20.9smp #1 SMP Mon Aug 18 11:32:15 EDT 2003 i686 i686
i386 GNU/Linux
# elvtune /dev/sda7
/dev/sda7 elevator ID 5
read_latency: 64
write_latency: 8192
max_bomb_segments: 6
I'll try on my laptop.
Reagards
Gaetano Mendola
Just for another data point, the default on my Debian 2.4.23-pre4 box is:
/dev/hdg elevator ID 3
read_latency: 128
write_latency: 512
max_bomb_segments: 0
--
greg