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Rusty Russell 11ab43084b tdb: workaround starvation problem in locking entire database.
We saw tdb_lockall() take 71 seconds under heavy load; this is because Linux
(at least) doesn't prevent new small locks being obtained while we're waiting
for a big log.

The workaround is to do divide and conquer using non-blocking chainlocks: if
we get down to a single chain we block.  Using a simple test program where
children did "hold lock for 100ms, sleep for 1 second" the time to do
tdb_lockall() dropped signifiantly.  There are ln(hashsize) locks taken in
the contended case, but that's slow anyway.

More analysis is given in my blog at http://rusty.ozlabs.org/?p=120

This may also help transactions, though in that case it's the initial
read lock which uses this gradual locking routine; the update-to-write-lock
code is separate and still tries to update in one go.

Even though ABI doesn't change, minor version bumped so behavior change
can be easily detected.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
2010-08-14 02:31:22 +09:30
..
2010-07-26 11:19:59 +10:00

compression - Various compression algorithms (MSZIP, lzxpress)
dnspython - Python module for working with DNS.
nss_wrapper - Wrapper for the user and group NSS API allowing the use 
              of other data sources.
popt - Command-line option parsing library
replace - Provides replacements for standard (POSIX, C99) functions 
          not provided by the host platform.
socket_wrapper - Wrapper library allowing TCP/IP traffic to be redirected 
                 over Unix domain sockets.
subunit - Utilities and bindings for working with the Subunit test result 
          reporting protocol.
talloc - Hierarchical pool based memory allocator 
tdb - Simple but fast key/value database library, supporting multiple writers
torture - Simple unit testing helper library