For the C standard char can be either signed or unsigned, it's up to the
compiler, but Redis assumed that it was signed in a few places.
The practical effect of this patch is that now Redis 2.6 will run
correctly in every system where char is unsigned, notably the RaspBerry
PI and other ARM systems with GCC.
Thanks to Georgi Marinov (@eesn on twitter) that reported the problem
and allowed me to use his RaspBerry via SSH to trace and fix the issue!
Because Redis 2.6 introduced new integer encodings it is no longer true
that if two entries have a different encoding they are not equal.
An old ziplist can be loaded from an RDB file generated with Redis 2.4,
in this case for instance a small unsigned integers is encoded with a
16 bit encoding, while in Redis 2.6 a more specific 8 bit encoding
format is used.
Because of this bug hashes ended with duplicated values or fields lookup
failed, causing many bad behaviors.
This in turn caused a crash while converting the ziplist encoded hash into
a real hash table because an assertion was raised on duplicated elements.
This commit fixes issue #547.
Many thanks to Pinterest's Marty Weiner and colleagues for discovering
the problem and helping us in the debugging process.
Because of the introduction of new integer encoding types for ziplists
in the 2.6 tree, the same integer value may have a different encoding in
different versions of the ziplist implementation. This means that the
encoding can NOT be used as a fast path in comparing integers.
1) One integer "immediate" encoding that can encode from 0 to 12 in the
encoding byte itself.
2) One 8 bit signed integer encoding that can encode 8 bit signed small
integers in a single byte.
The idea is to exploit all the not used bits we have around in a
backward compatible way.
To improve the performance of the ziplist implementation, some
functions have been converted to macros to avoid unnecessary stack
movement and duplicate variable assignments.
In the condition where the prevlen field of the next entry on insert
and delete operations needs more bytes to be properly encoded, the next
entry also needs to be updated with a new prevlen. This patch makes sure
that this effect cascades throughout the ziplist.
networking related stuff moved into networking.c
moved more code
more work on layout of source code
SDS instantaneuos memory saving. By Pieter and Salvatore at VMware ;)
cleanly compiling again after the first split, now splitting it in more C files
moving more things around... work in progress
split replication code
splitting more
Sets split
Hash split
replication split
even more splitting
more splitting
minor change
