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Status Not under consideration
Workspace Informix
Components Informix Server
Created by Guest
Created on Jan 26, 2017

Backup / ReadAhead Performance

To speedup backup time, it would be nice if Informix can read with more than 64k from disk.

Example 12G SAS SSD - read 100 GByte with dd iflag=direct:
Blocksize Throughput Time
64k 197 MB/Sec 519 Sec (8:39)
256k 438 MB/Sec 233 Sec (3:53)
2048k 1186 MB/Sec 86 Sec (1:26)

And that is what informix reads:

$ ontape -s -L 0 -t STDIO | dd of=/dev/null


# strace $( pidof oninit | sed 's/\([0-9]*\)/\-p \1/g') 2>&1|grep read
[pid 8391] io_submit(140133711802368, 1, {{pread, filedes:258, buf:0xfd2074400, nbytes:65536, offset:2810626048}}) = 1
[pid 8391] io_submit(140133711802368, 1, {{pread, filedes:258, buf:0xfd2085400, nbytes:65536, offset:2810691584}}) = 1
[pid 8391] io_submit(140133711802368, 1, {{pread, filedes:258, buf:0xfd128f400, nbytes:65536, offset:2810757120}}) = 1
[pid 8391] io_submit(140133711802368, 1, {{pread, filedes:258, buf:0xfd15c9400, nbytes:65536, offset:2810822656}}) = 1

Informix reads maximum with 64k blocksize... (if dbspace has 16k pagesize).

I also see no higher read blocksize during readahead while running normal queries with index/sequential scan. Maximum blocksize read:
32k