Details
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New Feature
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Status: Confirmed (View Workflow)
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Critical
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Resolution: Unresolved
Description
as a separate issue:
Motivated by CSC#7897, I've tried to see how much space can ANALYZE use. (So far my understanding was that max. temp dir usage would be rougly equal to size of the table w/o indexes).
Let's try this:
create table ten(a int);
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insert into ten values (0),(1),(2),(3),(4),(5),(6),(7),(8),(9);
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create table one_k(a int);
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insert into one_k select A.a + B.a* 10 + C.a * 100 from ten A, ten B, ten C;
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create table t1 (pk int primary key, col1 varchar(100)) charset=utf8;
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insert into t1 select A.a+B.a*1000, concat('val-', A.a+B.a*1000) from one_k A, one_k B;
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The table has 1M rows. Rows in the VARCHAR(100) column occupy less than
300 bytes (which is typical).
The table on disk:
-rw-rw---- 1 psergey psergey 44M Aug 1 23:09 t1.ibd
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Now,
analyze table t1 persistent for all;
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Breakpoint 4, unique_write_to_file_with_count (key=0x7ffebf2ce0a0 "\005", count=1, unique=0x7ffebf047ef0) at /home/psergey/dev2/10.0/sql/uniques.cc:53
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(gdb) print key
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$7 = (uchar *) 0x7ffebf2ce0a0 "\005"
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(gdb)
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(gdb) p unique->size
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$8 = 302
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It's writing 300 bytes, the unpacked length.
In total, we get:
Breakpoint 3, Unique::flush (this=0x7ffebf047ef0) at /home/psergey/dev2/10.0/sql/uniques.cc:379
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$46 = 281,734,200
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Breakpoint 3, Unique::flush (this=0x7ffebf047ef0) at /home/psergey/dev2/10.0/sql/uniques.cc:379
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$48 = 297,386,100
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...
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Breakpoint 3, Unique::flush (this=0x7ffebf047a30) at /home/psergey/dev2/10.0/sql/uniques.cc:379
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$47 = 4,194,304
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300MBit = 286 M, i.e. ANALYZE may require much more space than is occupied by the table (44M)
Attachments
Issue Links
- is blocked by
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MDEV-6915 Allow packed keys and packed values of non-sorted fields in the sort buffer
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- Closed
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- is duplicated by
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MDEV-10283 SEGV on ANALYZE LOCAL TABLE __ PERSISTENT FOR ALL
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- Closed
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- relates to
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- Stalled
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- Stalled
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- Closed
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