Ticket #671: d8af1fde685626283826ecaf52d4ac49cebdea98.patch

xapian-core/common/io_utils.cc

@@ -104 +104 @@
     throw Xapian::DatabaseError(m, e);
 }
 
+// dirty dirty hack that turns all preads into readaheads; preempts heavy disk
+// io operations
+bool IS_READAHEAD = false;
+void set_readahead(bool val) {
+    IS_READAHEAD = val;
+}
+
 void
 io_read_block(int fd, char * p, size_t n, off_t b)
 {
@@ -113 +120 @@
     // per block read.
 #ifdef HAVE_PREAD
     while (true) {
+        if (IS_READAHEAD) {
+            // readahead has reversed order of parameters to pread, for some reason...
+            readahead(fd, o, n);
+            return;
+        }
         ssize_t c = pread(fd, p, n, o);
         // We should get a full read most of the time, so streamline that case.
         if (usual(c == ssize_t(n)))

xapian-core/common/io_utils.h

@@ -47 +47 @@
 #endif
 }
 
+void set_readahead(bool val);
+
 inline bool io_full_sync(int fd)
 {
 #ifdef F_FULLFSYNC

xapian-core/matcher/multimatch.cc

@@ -32 +32 @@
 #include "debuglog.h"
 #include "submatch.h"
 #include "localsubmatch.h"
+#include "io_utils.h"
 #include "omassert.h"
 #include "api/omenquireinternal.h"
 #include "realtime.h"
@@ -350 +351 @@
     }
 
     stats.set_query(query);
+
+    set_readahead(true);
+    // readahead all the blocks we're about to read
+        for (size_t leaf = 0; leaf < leaves.size(); ++leaf) {
+                SubMatch * submatch = leaves[leaf].get();
+                submatch->prepare_match(true, stats);
+    }
+    set_readahead(false);
+
     prepare_sub_matches(leaves, errorhandler, stats);
     stats.set_bounds_from_db(db);
 }