Masakazu Kitajo created TS-4316:
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Summary: Slot accelerator doesn't effect under certain condition
Key: TS-4316
URL: https://issues.apache.org/jira/browse/TS-4316
Project: Traffic Server
Issue Type: Bug
Components: MIME
Reporter: Masakazu Kitajo
Slot accelerators seem to not effect if the stored slot number is 14 or 15.
This is because {{mime_hdr_set_accelerators_and_presence_bits()}} regards slot
number 14+ as "unknown" and stores MIME_FIELD_SLOTNUM_UNKNOWN(14) to an
accelerator, and it causes slower search. Although there is no critical effect,
it would decreases performance slightly.
The numbers, 14 and 15, comes from constants below in MIME.h:
{code}
#define MIME_FIELD_SLOTNUM_BITS 4
#define MIME_FIELD_SLOTNUM_MASK ((1 << MIME_FIELD_SLOTNUM_BITS) - 1)
#define MIME_FIELD_SLOTNUM_MAX (MIME_FIELD_SLOTNUM_MASK - 1)
#define MIME_FIELD_SLOTNUM_UNKNOWN MIME_FIELD_SLOTNUM_MAX
{code}
MIME_FIELD_SLOTNUM_MASK is 15.
MIME_FIELD_SLOTNUM_MAX is 14.
MIME_FIELD_SLOTNUM_UNKNOWN is 14 too.
Though it still needs more careful confirmation, it seems we can simply change
{{MIME_FIELD_SLOTNUM_UNKNOWN}} to the value of {{MIME_FIELD_SLOTNUM_MASK}}
(15). But we still cannot use 15.
To use 15 as a valid slot number in slot accelerators, we need to change
{{MIME_FIELD_SLOTNUM_UNKNOWN}} to 16 or -1, however it would need to change
some codes also (not only the number).
This bug has been found while I was tackling TS-4313.
https://github.com/apache/trafficserver/pull/542#discussion-diff-58226891
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