[
https://issues.apache.org/jira/browse/TS-4316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15470810#comment-15470810
]
Masakazu Kitajo commented on TS-4316:
-------------------------------------
{quote}
Those fields are still accessible, it just requires a linear search.
{quote}
Yes, that is the inefficiency what I wanted to say. Slot number 14 and 15 are
unlucky slot numbers because we could have free slots that can access without
linear search. Ideally, the two slots should be used after we used all slot
0-13 of each slot IDs.
I'm not sure how much the expantion improves performance, but it could work
because we use lots of headers nowdays and some of them should be added as
WKSs. Such as H2 pseudo headers.
> 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
> Assignee: Alan M. Carroll
> Fix For: 7.0.0
>
>
> 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
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
