Re: reads by KTSJ

What size is the extent that it's sitting inside, and which block of the extent is it ?

Regards
Jonathan Lewis

On Wed, May 13, 2020 at 10:07 AM Noveljic Nenad <nenad.noveljic_at_vontobel.com> wrote:

> Thank you, Jonathan.
>
>
>
> I randomly picked the following block:
>
>
>
> SQL> _at_ashtop
> program2,event2,p1,p1text,p2,p2text,p3,p3text,sql_id,top_level_sql_opcode
> "program2 like '(W%' and event is not null" "to_date('2020-05-12
> 13:37:15')" "to_date('2020-05-12 14:37:15')"
>
>
>
>
> Total
> Distinct
>
> Seconds AAS %This PROGRAM2
> EVENT2 P1
> P1TEXT P2
> P2TEXT P3 P3TEXT
> SQL_ID TOP_LEVEL_SQL_OPCODE FIRST_S Execs Seen
>
> --------- ------- ------- ----------------------------------------
> ------------------------------------------ ----------
> ------------------------------ ---------- ------------------------------
> ---------- ------------------------------ -------------
> -------------------- ------------- ----------
>
> 1 .0 0% | (WnnA) db file
> sequential read 12
> file# 419748
> block# 1
> blocks 0
> 2020-05:56:54 1
>
>
>
> It belongs to a table segment:
>
>
>
> select owner,segment_name,partition_name,segment_type from dba_extents
> where file_id=12 and 419748 between block_id and block_id+blocks-1 ;
>
>
>
> OWNER SEGMENT_NAME
> PARTITION_NAME SEGMENT_TYPE
>
> ------------------------------ ------------------------------
> ------------------------------ ------------------
>
> XXXXXXXX
> XXXXXXXXXXXXXXXXXXXXXX
> TABLE
>
>
>
>
>
> Below is the the symbolic dump.
>
>
>
> Start dump data blocks tsn: 16 file#:12 minblk 419748 maxblk 419748
>
> Block dump from cache:
>
> Dump of buffer cache at level 3 for pdb=0 tsn=16 rdba=50751396
>
> Block dump from disk:
>
> buffer tsn: 16 rdba: 0x030667a4 (12/419748)
>
> scn: 0x1211b61c3d seq: 0x01 flg: 0x04 tail: 0x1c3d0601
>
> frmt: 0x02 chkval: 0x51a5 type: 0x06=trans data
>
> Hex dump of block: st=0, typ_found=1
>
>
>
> The block seems empty.
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
> *From:* oracle-l-bounce_at_freelists.org <oracle-l-bounce_at_freelists.org> *On
> Behalf Of *Jonathan Lewis
> *Sent:* Mittwoch, 13. Mai 2020 09:36
> *To:* ORACLE-L (oracle-l_at_freelists.org) <oracle-l_at_freelists.org>
> *Subject:* Re: reads by KTSJ
>
>
>
>
>
> As Mladen said, KTS is all about space management, and one of the key
> functions of the Wnnn processes is to anticipate space requirements and
> pre-allocate, which applies particularly to extending tablespaces in
> advance of demand and extending segments (particularly securefile segments,
> I think) in advance.
>
>
>
> You said the buffer busy waits were in the user schema - which presumably
> means they were for blocks that are currently part of some user segments.
> If this is correct, what class of block would they be - I'd expect them to
> be bitmap space management blocks. I can imagine Oracle using several Wnnn
> processes to add a large amount of space to a securefile segment and having
> to update the L3 and L2 bitmap blocks for that segment - and having to
> queue to update the bitmaps.
>
>
>
> Regards
>
> Jonathan Lewis
>
>
>
>
>
> On Tue, May 12, 2020 at 10:05 PM Noveljic Nenad <
> nenad.noveljic_at_vontobel.com> wrote:
>
> I started occasionally seeing KTSJ slaves heavily waiting on “free buffer
> waits” and “db file sequential read” after upgrading from 18.7.0.0.190716
> to 19.7.0.0.200414:
>
>
>
> SQL> _at_ash_wait_chains2 "program2||' '||event2||' '||module||' '||action"
> "program2 like '(W%'" "to_date('2020-05-12 13:37:15')"
> "to_date('2020-05-12 14:37:15')"
>
>
>
> -- Display ASH Wait Chain Signatures script v0.5 BETA by Tanel Poder (
> http://blog.tanelpoder.com )
>
>
>
> %This SECONDS AAS WAIT_CHAIN
> FIRST_SEEN
> LAST_SEEN
>
> ------ ---------- -------
> ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
> ------------------- -------------------
>
> 22% 310 .1 -> (Wnnn) free buffer waits KTSJ KTSJ Slave ->
> (DBWnnn) db file parallel write
> 2020-05-12
> 13:46:55 2020-05-12 13:48:40
>
> 10% 144 .0 -> (Wnnn) db file sequential read KTSJ KTSJ
> Slave
> 2020-05-12
> 13:46:54 2020-05-12 13:48:52
>
> 10% 144 .0 -> (WnnA) free buffer waits KTSJ KTSJ Slave ->
> (DBWnnn) db file parallel write
> 2020-05-12
> 13:46:55 2020-05-12 13:57:13
>
> 7% 104 .0 -> (WnnA) db file sequential read KTSJ KTSJ
> Slave
> 2020-05-12 13:46:54 2020-05-12
> 13:57:11
>
>
>
> Some of the affected processes have the following entries in the trace
> file:
>
>
>
> *** SESSION ID:(1202.8580) 2020-05-12T13:46:54.295884+02:00
>
> *** CLIENT ID:() 2020-05-12T13:46:54.295916+02:00
>
> *** SERVICE NAME:(SYS$BACKGROUND) 2020-05-12T13:46:54.295947+02:00
>
> *** MODULE NAME:(KTSJ) 2020-05-12T13:46:54.295978+02:00
>
> *** ACTION NAME:(KTSJ Slave) 2020-05-12T13:46:54.296009+02:00
>
> *** CLIENT DRIVER:() 2020-05-12T13:46:54.296039+02:00
>
>
>
> [ktspsc_segmon] submitted segfix task
>
> [ktspsc_segmon] submitted segfix task
>
> [ktspsc_segmon] submitted segfix task
>
>
>
>
>
> The tablespaces are autoextensible, but I don’t know if they were extended
> during this time period. The IO performance is OK.
>
>
>
> I examined one of the read bloccks – it belongs to a user schema, nothing
> special about it:
>
>
>
> How to figure out what might have caused this KTSJ slave activity?
>
>
>
> Best regards,
>
>
>
> Nenad
>
>
>
> https://nenadnoveljic.com/blog/
>
>
>
>
>
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