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uplex-varnish
slash
Commits
085ba7b4
Unverified
Commit
085ba7b4
authored
Jul 24, 2023
by
Nils Goroll
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085ba7b4
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@@ -16,11 +16,99 @@ to old.
...
@@ -16,11 +16,99 @@ to old.
SLASH/ Changes
SLASH/ Changes
==============
==============
fellow
======
.. https://gitlab.com/uplex/varnish/slash/-/commit/
* The allocation policy for disk regions has been improved. This
should reduce fragmentation and pressure on LRU as well as improve
response times (`a0e8e8f779f4ad8569ccc9c3b7eaee08dc79cfa4`_).
.. _a0e8e8f779f4ad8569ccc9c3b7eaee08dc79cfa4: https://gitlab.com/uplex/varnish/slash/-/commit/a0e8e8f779f4ad8569ccc9c3b7eaee08dc79cfa4
* The ``objsize_max`` tunable has been added, which defaults to 1/4 of
* The ``objsize_max`` tunable has been added, which defaults to 1/4 of
*dsksize*.
*dsksize* (`bef3d014a6a31a6993169ef1aa95aedec2d4aa23`_).
.. _bef3d014a6a31a6993169ef1aa95aedec2d4aa23: https://gitlab.com/uplex/varnish/slash/-/commit/bef3d014a6a31a6993169ef1aa95aedec2d4aa23
The tunable now allows SLASH/ to make an educated guess about how
much space at most to allocate in advance when the object size is
not known upfront, for example with *chunked encoding*.
* Fixed two issues where reservations and their limits were not
calculated correctly (`a02dd5c5a1c13c9fcdc8e1a5d5281ddf69b3148f`_,
`8b700a275cb977d7c6d703a0e2a6ca8a7310f0c3`_).
.. _a02dd5c5a1c13c9fcdc8e1a5d5281ddf69b3148f: https://gitlab.com/uplex/varnish/slash/-/commit/a02dd5c5a1c13c9fcdc8e1a5d5281ddf69b3148f
.. _8b700a275cb977d7c6d703a0e2a6ca8a7310f0c3: https://gitlab.com/uplex/varnish/slash/-/commit/8b700a275cb977d7c6d703a0e2a6ca8a7310f0c3
* The ``chunk_bytes`` tunable now has a new hard cap at less than
1/1024 of the memory cache size. This is to avoid lockups when the
memory cache becomes too fragmented to serve larger allocation
requests (`#11`_, `da63a5b836e37f27f1759a37446c117d37284650`_).
.. _da63a5b836e37f27f1759a37446c117d37284650: https://gitlab.com/uplex/varnish/slash/-/commit/da63a5b836e37f27f1759a37446c117d37284650
.. _#11: https://gitlab.com/uplex/varnish/slash/-/issues/11
* Previously, when multiple requests accessed the same disk object
(not yet present in RAM), they would race to create it, allocating
memory and, if they lost the race, freeing it again.
This is now avoided using a "wait table": A hash table of
configurable size serializes operations on each hash value, which is
derived from the location and size of an object on disk.
The size of the wait table approximates a limit to the number of
objects which can be initially read from disk concurrently. Note
that this does not affect reading object bodies, just the object
metadata and headers.
The size of the table can be adjusted using the new
``wait_table_exponent`` tunable, which is in powers of two, so, for
example, the default of 10 results in a hash table of size 2^10 =
1024. Each hash table entry uses approximately 128 bytes
(`d5c1bbd7b14b8736a641da4c2c28d979e917d020`_).
.. _d5c1bbd7b14b8736a641da4c2c28d979e917d020: https://gitlab.com/uplex/varnish/slash/-/commit/d5c1bbd7b14b8736a641da4c2c28d979e917d020
* When cache memory is tight and LRU is running, allocation requests
have always been prioritized (in this order): free operations > log
operations > metadata > objects > reserves.
This priority list has now been extended to weigh operations on
object operations which are already in progress over creation of new
objects - the idea being that, when cache memory is under pressure,
any operations which are required to finish before memory can be
freed again should be prioritized.
The new list of priorities is: free operations > log operations >
metadata > object body iterations > object fetch operations > new
cache objects > initial object reads from disk > reserves
(`4dcda2c00ad40f0c471c1f9fa078d8d1cc17d32e`_)
As an exception, requests to ``Vary`` headers are prioritized like
object body iterations, because they might happen while holding the
``objhead`` mutex during cache lookups. Also ``Vary`` access is
handled like an object access with respect to LRU.
.. _4dcda2c00ad40f0c471c1f9fa078d8d1cc17d32e: https://gitlab.com/uplex/varnish/slash/-/commit/4dcda2c00ad40f0c471c1f9fa078d8d1cc17d32e
.. _491339c242c5a94f4b2ed448e531abe6deb60a88: https://gitlab.com/uplex/varnish/slash/-/commit/491339c242c5a94f4b2ed448e531abe6deb60a88
.. _94d37731bd45ec0e53883ec256125277a74e92aa: https://gitlab.com/uplex/varnish/slash/-/commit/94d37731bd45ec0e53883ec256125277a74e92aa
* The ``oa_present`` bit field in varnish-cache is now restored when
an object is read from disk for the first time after a cache
start. This avoids I/O and reduces cache memory requirements when
the ``Vary`` response header is not used
(`fc1af457e52c272bdeea8bd3b207e6f96fad8dbe`_).
.. _fc1af457e52c272bdeea8bd3b207e6f96fad8dbe: https://gitlab.com/uplex/varnish/slash/-/commit/fc1af457e52c272bdeea8bd3b207e6f96fad8dbe
* Memory requirements of cache misses ("busy objects") have been
reduced substantially (from >12KB to <4KB) (`#16`_).
.. _#16: https://gitlab.com/uplex/varnish/slash/-/issues/16
The tunable is going to be used to allow SLASH/ to make an educated
Base of the changelog: `e3a454096759cafd30d9008f4b11cc754297b250`_
guess about how much space to allocate in advance when the object
size is not known upfront, for example with *chunked encoding*.
Base of the changelog:
e3a454096759cafd30d9008f4b11cc754297b250
.. _e3a454096759cafd30d9008f4b11cc754297b250: https://gitlab.com/uplex/varnish/slash/-/commit/
e3a454096759cafd30d9008f4b11cc754297b250
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