Revert "Posix memory map advise cache retention policy."

include/bitcoin/database/impl/memory/mmap_staging.ipp

@@ -831,21 +831,10 @@ template <size_t... Index>
 bool CLASS::settle_write_(size_t from, size_t to,
     std::index_sequence<Index...>) NOEXCEPT
 {
-    const auto settle = [this, from, to]<size_t Column>() NOEXCEPT
-    {
-        const auto offset = to_width<Column>(from);
-        const auto size = to_width<Column>(to) - offset;
-        const auto success = pwrite_all(opened_[Column],
-            std::next(memory_map_[Column], offset), size, offset);
-
-        // Settled bytes are read only through the map, drop the write cache.
-        if (success)
-            ::evict(opened_[Column], offset, size);
-
-        return success;
-    };
-
-    return (settle.template operator()<Index>() && ...);
+    return (pwrite_all(opened_[Index],
+        std::next(memory_map_[Index], to_width<Index>(from)),
+        to_width<Index>(to) - to_width<Index>(from),
+        to_width<Index>(from)) && ...);
 }
 
 #endif // MANAGE_STAGING

include/bitcoin/database/impl/memory/mmap_storage.ipp

@@ -26,7 +26,6 @@
 #include <shared_mutex>
 #include <bitcoin/database/define.hpp>
 #include <bitcoin/database/file/file.hpp>
-#include <bitcoin/database/memory/mman.hpp>
 
 namespace libbitcoin {
 namespace database {
@@ -81,13 +80,6 @@ code CLASS::open() NOEXCEPT
             filenames_.at(index), random_))
             return ec;
 
-    // Staged bytes are read only through the map once settled, so exclude
-    // descriptor writes from file system caching (macOS otherwise retains
-    // settled pages in cache, starving the mapped read set under pressure).
-    if (staged_)
-        for (const auto& descriptor: opened_)
-            ::uncache(descriptor);
-
     // logical_ is the shared row count, derived from column 0's byte size.
     size_t bytes{};
     if (const auto ec = file::size_ex(bytes, opened_.front()))

include/bitcoin/database/memory/mman.hpp

@@ -6,7 +6,6 @@
 #include <bitcoin/database/define.hpp>
 
 #if !defined(HAVE_MSC)
-    #include <fcntl.h>
     #include <sys/mman.h>
     #include <sys/stat.h>
     #include <sys/types.h>
@@ -59,37 +58,4 @@ int fallocate(int fd, int, off_t offset, off_t len) NOEXCEPT;
 
 #endif // HAVE_MSC
 
-/// Exclude descriptor read/write from file system caching (advisory,
-/// effective only on macOS). Staged bytes are read only through the map
-/// once settled, so cache retention of the written pages can only displace
-/// more useful pages.
-#if defined(HAVE_APPLE)
-inline int uncache(int fd) NOEXCEPT
-{
-    return ::fcntl(fd, F_NOCACHE, 1);
-}
-#else
-inline int uncache(int) NOEXCEPT
-{
-    return 0;
-}
-#endif
-
-/// Drop cached pages of a written range (advisory, effective only on Linux,
-/// where uncache is a no-op). The sync makes the range clean so that the
-/// eviction is not skipped, which only hastens settled write durability.
-#if defined(HAVE_LINUX)
-inline int evict(int fd, size_t offset, size_t size) NOEXCEPT
-{
-    return (::fdatasync(fd) == -1) ? -1 : ::posix_fadvise(fd,
-        static_cast<off_t>(offset), static_cast<off_t>(size),
-        POSIX_FADV_DONTNEED);
-}
-#else
-inline int evict(int, size_t, size_t) NOEXCEPT
-{
-    return 0;
-}
-#endif
-
 #endif