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Database-level statistics (MON$STAT_GROUP = 0) may contain multiple rows under concurrent load [CORE5179] #5460

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firebird-issue-importer opened this issue Mar 30, 2016 · 9 comments

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@firebird-issue-importer

Submitted by: @pavel-zotov

Attachments:
multiple_rows_in_singleton_when_select_from_mon-io_stats_where_mon-stat_group_equ_0.7z
test-concurrent-querying-to-mon_io.7z

1) Unpack attached .7z, restore fbk.
2) Open "getfbarch.bat" in your text editor and correct settings: specify path to ISQL, host/port of server and path to database file that you've just restored.
3) Copy files "getfbarch.bat" and "getfbarch.sql" in two different folders.
4) Launch "getfbarch.bat" in both directories. It will create log with name "getfbarch.log".
5) Wait 1-5 minutes. Sooner of all, after short time both sessions will be closed, and logs will contain smth. like this:

...
30.03.2016 17:32:27,43. Iter #⁠ 259
30.03.2016 17:32:27,70. Iter #⁠ 260
30.03.2016 17:32:27,98. Finish.
Statement failed, SQLSTATE = 21000
multiple rows in singleton select
After line 1 in file getfbarch.sql

This mean that query:

 select 1 from mon$io\_stats where mon$stat\_group = 0 into n;

===
-- got TWO records, despite that stat_group = 0 is TOP-LEVEL kind of statistics (i.e. it's of the whole database).

Number of iterations that needed for reproducing problem differ: one may to get trouble after 20 but later - wait until 300...400 iterations will pass.

Commits: a441ea9 c3858e1

====== Test Details ======

High concurrent workload with undefined time is required for checking.

Several new issues were found during fix verification but seems that all of them do not relate to ticket subj: build LI-T4.0.0.113 crashed.
Unfortunately, crashes could not be reproduced in 100% (they occur only on my Linux server and Windows PC as client).

Last vers. of test batch+sql see in attached 7z.

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@firebird-issue-importer firebird-issue-importer commented Mar 30, 2016

Modified by: @pavel-zotov

Attachment: multiple_rows_in_singleton_when_select_from_mon-io_stats_where_mon-stat_group_equ_0.7z [ 12933 ]

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@firebird-issue-importer firebird-issue-importer commented Mar 30, 2016

Commented by: @pavel-zotov

PS. On database with big size (I have 100 Gb) one may to get exception about "multiple rows" on just first iteration (probability is about 99% if you will run batch with gap about 2-3 seconds while switching between windows).

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@firebird-issue-importer firebird-issue-importer commented Mar 30, 2016

Modified by: @dyemanov

assignee: Dmitry Yemanov [ dimitr ]

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@firebird-issue-importer firebird-issue-importer commented Mar 30, 2016

Modified by: @dyemanov

Version: 3.0 RC1 [ 10584 ]

Fix Version: 3.0.0 [ 10740 ]

summary: Query "select from mon$io_stats where mon$stat_group = 0" /* __DATABASE__ level statistics*/ can return more than one record when this data is queried by >= 2 attachments => Database-level statistics (MON$STAT_GROUP = 0) may contain multiple rows under concurrent load

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@firebird-issue-importer firebird-issue-importer commented Mar 31, 2016

Commented by: @dyemanov

Fixed in v4.0, please test it thoroughly to allow backporting into v3.0.

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@firebird-issue-importer firebird-issue-importer commented Mar 31, 2016

Modified by: @dyemanov

Version: 4.0 Initial [ 10621 ]

Fix Version: 4.0 Alpha 1 [ 10731 ]

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@firebird-issue-importer firebird-issue-importer commented Apr 2, 2016

Modified by: @dyemanov

status: Open [ 1 ] => Resolved [ 5 ]

resolution: Fixed [ 1 ]

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@firebird-issue-importer firebird-issue-importer commented Apr 6, 2016

Modified by: @pavel-zotov

status: Resolved [ 5 ] => Resolved [ 5 ]

QA Status: No test => Cannot be tested

Test Details: High concurrent workload with undefined time is required for checking.

Several new issues were found during fix verification but seems that all of them do not relate to ticket subj: build LI-T4.0.0.113 crashed.
Unfortunately, crashes could not be reproduced in 100% (they occur only on my Linux server and Windows PC as client).

Last vers. of test batch+sql see in attached 7z.

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@firebird-issue-importer firebird-issue-importer commented Apr 6, 2016

Modified by: @pavel-zotov

Attachment: test-concurrent-querying-to-mon_io.7z [ 12935 ]

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