[svn-r5510] Purpose:

    Code cleanup/bug fix

Description:
    The "metadata accumulator" cache in the library (which is designed to catch
    small metadata writes/reads and bundle them together into larger I/O
    buffers) was incorrectly detecting the important case of metadata pieces
    being written sequentially to the file, adjoining but not overlapping.

    Additionally, the metadata accumulator was not being used to cache data
    read in from disk, only caching writes.

Solution:
    Fix accumulator to correctly cache adjoining metadata writes and also to
    cache metadata read from disk.

    Between these two fixes, the number of I/O requests which resulted in actual
    reads/writes to the filesystem dropped from 393 requests to 82 for the
    particular test I was using. :-)

Platforms tested:
    Solaris 2.7 (arabica) w/FORTRAN & FreeBSD 4.5 (sleipnir) w/C++

2 files changed, 103 insertions, 57 deletions

diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 8683f86..1ec6ce2 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -166,6 +166,9 @@ Documentation
 New Features
 ============
 
+    * Improved internal metadata caching, which can reduce the number of actual
+      I/O calls made by a substantial amount, improving
+      performance.  QAK - 2002/06/03
     * Added 'closing' parameter to VFL 'flush' callback function and H5FDflush.
       This allows the library to indicate that the file will be closed
       immediately following the call to 'flush' and can be used to avoid actions
diff --git a/src/H5FD.c b/src/H5FD.c
index 5ec101e..30cbbee 100644
--- a/src/H5FD.c
+++ b/src/H5FD.c
@@ -2082,7 +2082,7 @@ H5FDread(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t size
 
     /* Do the real work */
     if (H5FD_read(file, type, dxpl_id, addr, size, buf)<0)
-	HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "file read request failed");
+	HRETURN_ERROR(H5E_VFL, H5E_READERROR, FAIL, "file read request failed");
 
     FUNC_LEAVE(SUCCEED);
 }
@@ -2127,76 +2127,111 @@ H5FD_read(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t siz
 #endif
 
     /* Check if this information is in the metadata accumulator */
-    if((file->feature_flags&H5FD_FEAT_ACCUMULATE_METADATA) &&
-        H5F_addr_overlap(addr,size,file->accum_loc,file->accum_size)) {
-
-        unsigned char *read_buf=(unsigned char *)buf; /* Pointer to the buffer being read in */
-        size_t amount_read;         /* Amount to read at a time */
+    if((file->feature_flags&H5FD_FEAT_ACCUMULATE_METADATA) && type!=H5FD_MEM_DRAW) {
+        /* Current read overlaps with metadata accumulator */
+        if(H5F_addr_overlap(addr,size,file->accum_loc,file->accum_size)) {
+            unsigned char *read_buf=(unsigned char *)buf; /* Pointer to the buffer being read in */
+            size_t amount_read;         /* Amount to read at a time */
 #ifndef NDEBUG
-        hsize_t tempamount_read;         /* Amount to read at a time */
+            hsize_t tempamount_read;         /* Amount to read at a time */
 #endif /* NDEBUG */
-        hsize_t read_off;           /* Offset to read from */
+            hsize_t read_off;           /* Offset to read from */
 
-        /* Double check that we aren't reading raw data */
-        assert(type!=H5FD_MEM_DRAW);
+            /* Double check that we aren't reading raw data */
+            assert(type!=H5FD_MEM_DRAW);
 
-        /* Read the part before the metadata accumulator */
-        if(addr<file->accum_loc) {
-            /* Set the amount to read */
-            H5_ASSIGN_OVERFLOW(amount_read,file->accum_loc-addr,hsize_t,size_t);
+            /* Read the part before the metadata accumulator */
+            if(addr<file->accum_loc) {
+                /* Set the amount to read */
+                H5_ASSIGN_OVERFLOW(amount_read,file->accum_loc-addr,hsize_t,size_t);
 
-            /* Dispatch to driver */
-            if ((file->cls->read)(file, type, dxpl_id, addr, amount_read, read_buf)<0)
-                HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "driver read request failed");
+                /* Dispatch to driver */
+                if ((file->cls->read)(file, type, dxpl_id, addr, amount_read, read_buf)<0)
+                    HRETURN_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read request failed");
 
-            /* Adjust the buffer, address & size */
-            read_buf+=amount_read;
-            addr+=amount_read;
-            size-=amount_read;
-        } /* end if */
+                /* Adjust the buffer, address & size */
+                read_buf+=amount_read;
+                addr+=amount_read;
+                size-=amount_read;
+            } /* end if */
 
-        /* Copy the part overlapping the metadata accumulator */
-        if(size>0 && (addr>=file->accum_loc && addr<(file->accum_loc+file->accum_size))) {
-            /* Set the offset to "read" from */
-            read_off=addr-file->accum_loc;
+            /* Copy the part overlapping the metadata accumulator */
+            if(size>0 && (addr>=file->accum_loc && addr<(file->accum_loc+file->accum_size))) {
+                /* Set the offset to "read" from */
+                read_off=addr-file->accum_loc;
 
-            /* Set the amount to "read" */
+                /* Set the amount to "read" */
 #ifndef NDEBUG
-            tempamount_read = file->accum_size-read_off;
-            H5_CHECK_OVERFLOW(tempamount_read,hsize_t,size_t);
-            amount_read = MIN(size, (size_t)tempamount_read);
+                tempamount_read = file->accum_size-read_off;
+                H5_CHECK_OVERFLOW(tempamount_read,hsize_t,size_t);
+                amount_read = MIN(size, (size_t)tempamount_read);
 #else /* NDEBUG */
-            amount_read = MIN(size, (size_t)(file->accum_size-read_off));
+                amount_read = MIN(size, (size_t)(file->accum_size-read_off));
 #endif /* NDEBUG */
 
-            /* Copy the data out of the buffer */
-            HDmemcpy(read_buf,file->meta_accum+read_off,amount_read);
+                /* Copy the data out of the buffer */
+                HDmemcpy(read_buf,file->meta_accum+read_off,amount_read);
 
-            /* Adjust the buffer, address & size */
-            read_buf+=amount_read;
-            addr+=amount_read;
-            size-=amount_read;
-        } /* end if */
+                /* Adjust the buffer, address & size */
+                read_buf+=amount_read;
+                addr+=amount_read;
+                size-=amount_read;
+            } /* end if */
+
+            /* Read the part after the metadata accumulator */
+            if(size>0 && addr>=(file->accum_loc+file->accum_size)) {
+                /* Dispatch to driver */
+                if ((file->cls->read)(file, type, dxpl_id, addr, size, read_buf)<0)
+                    HRETURN_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read request failed");
 
-        /* Read the part after the metadata accumulator */
-        if(size>0 && addr>=(file->accum_loc+file->accum_size)) {
-            /* Dispatch to driver */
-            if ((file->cls->read)(file, type, dxpl_id, addr, size, read_buf)<0)
-                HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "driver read request failed");
+                /* Adjust the buffer, address & size */
+                read_buf+=size;
+                addr+=size;
+                size-=size;
+            } /* end if */
 
-            /* Adjust the buffer, address & size */
-            read_buf+=size;
-            addr+=size;
-            size-=size;
+            /* Make certain we've read it all */
+            assert(size==0);
         } /* end if */
+        /* Current read doesn't overlap with metadata accumulator, read it into accumulator */
+        else {
+            /* Flush current contents, if dirty */
+            if(file->accum_dirty) {
+                if ((file->cls->write)(file, H5FD_MEM_DEFAULT, dxpl_id, file->accum_loc, file->accum_size, file->meta_accum)<0)
+                    HRETURN_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write request failed");
+
+                /* Reset accumulator dirty flag */
+                file->accum_dirty=FALSE;
+            } /* end if */
+
+            /* Cache the new piece of metadata */
+            /* Check if we need to reallocate the buffer */
+            if(size>file->accum_buf_size) {
+                /* Reallocate the metadata accumulator buffer */
+                if ((file->meta_accum=H5FL_BLK_REALLOC(meta_accum,file->meta_accum,size))==NULL)
+                    HRETURN_ERROR(H5E_RESOURCE, H5E_NOSPACE, FAIL, "unable to allocate metadata accumulator buffer");
 
-        /* Make certain we've read it all */
-        assert(size==0);
+                /* Note the new buffer size */
+                file->accum_buf_size=size;
+            } /* end if */
+
+            /* Update accumulator information */
+            file->accum_loc=addr;
+            file->accum_size=size;
+            file->accum_dirty=FALSE;
+
+            /* Read into accumulator */
+            if ((file->cls->read)(file, H5FD_MEM_DEFAULT, dxpl_id, file->accum_loc, file->accum_size, file->meta_accum)<0)
+                HRETURN_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read request failed");
+
+            /* Copy into buffer */
+            HDmemcpy(buf,file->meta_accum,size);
+        } /* end else */
     } /* end if */
     else {
         /* Dispatch to driver */
         if ((file->cls->read)(file, type, dxpl_id, addr, size, buf)<0)
-            HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "driver read request failed");
+            HRETURN_ERROR(H5E_VFL, H5E_READERROR, FAIL, "driver read request failed");
     } /* end else */
 
     FUNC_LEAVE(SUCCEED);
@@ -2243,7 +2278,7 @@ H5FDwrite(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t siz
 
     /* The real work */
     if (H5FD_write(file, type, dxpl_id, addr, size, buf)<0)
-	HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "file write request failed");
+	HRETURN_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "file write request failed");
 
     FUNC_LEAVE(SUCCEED);
 }
@@ -2295,7 +2330,7 @@ H5FD_write(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t si
         /* Check if there is already metadata in the accumulator */
         if(file->accum_size>0) {
             /* Check if the piece of metadata being written adjoins or is inside the metadata accumulator */
-            if((addr>=file->accum_loc && addr <(file->accum_loc+file->accum_size))
+            if((addr>=file->accum_loc && addr<=(file->accum_loc+file->accum_size))
                 || ((addr+size)>file->accum_loc && (addr+size)<=(file->accum_loc+file->accum_size))
                 || (addr<file->accum_loc && (addr+size)>file->accum_loc)) {
 
@@ -2416,8 +2451,12 @@ H5FD_write(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t si
             /* New piece of metadata doesn't adjoin or overlap the existing accumulator */
             else {
                 /* Write out the existing metadata accumulator, with dispatch to driver */
-                if ((file->cls->write)(file, H5FD_MEM_DEFAULT, dxpl_id, file->accum_loc, file->accum_size, file->meta_accum)<0)
-                    HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "driver write request failed");
+                if(file->accum_dirty) {
+                    if ((file->cls->write)(file, H5FD_MEM_DEFAULT, dxpl_id, file->accum_loc, file->accum_size, file->meta_accum)<0)
+                        HRETURN_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write request failed");
+                    /* Reset accumulator dirty flag */
+                    file->accum_dirty=FALSE;
+                } /* end if */
 
                 /* Cache the new piece of metadata */
                 /* Check if we need to reallocate the buffer */
@@ -2430,10 +2469,12 @@ H5FD_write(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t si
                     file->accum_buf_size=size;
                 } /* end if */
 
-                /* Store the piece of metadata in the accumulator */
+                /* Update the metadata accumulator information */
                 file->accum_loc=addr;
                 file->accum_size=size;
                 file->accum_dirty=TRUE;
+
+                /* Store the piece of metadata in the accumulator */
                 HDmemcpy(file->meta_accum,buf,size);
             } /* end else */
         } /* end if */
@@ -2449,17 +2490,19 @@ H5FD_write(H5FD_t *file, H5FD_mem_t type, hid_t dxpl_id, haddr_t addr, size_t si
                 file->accum_buf_size=size;
             } /* end if */
 
-            /* Store the piece of metadata in the accumulator */
+            /* Update the metadata accumulator information */
             file->accum_loc=addr;
             file->accum_size=size;
             file->accum_dirty=TRUE;
+
+            /* Store the piece of metadata in the accumulator */
             HDmemcpy(file->meta_accum,buf,size);
         } /* end else */
     } /* end if */
     else {
         /* Dispatch to driver */
         if ((file->cls->write)(file, type, dxpl_id, addr, size, buf)<0)
-            HRETURN_ERROR(H5E_VFL, H5E_CANTINIT, FAIL, "driver write request failed");
+            HRETURN_ERROR(H5E_VFL, H5E_WRITEERROR, FAIL, "driver write request failed");
     } /* end else */
 
     FUNC_LEAVE(SUCCEED);