git-p4: use -m when running p4 changes

Simply running "p4 changes" on a large branch can result in a "too
many rows scanned" error from the Perforce server. It is better to
use a sequence of smaller calls to "p4 changes", using the "-m"
option to limit the size of each call.

Signed-off-by: Lex Spoon <lex@lexspoon.org>
Acked-by: Luke Diamand <luke@diamand.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-p4.txt

@@ -225,9 +225,20 @@ Git repository:
 	they can find the p4 branches in refs/heads.
 
 --max-changes <n>::
-	Limit the number of imported changes to 'n'.  Useful to
-	limit the amount of history when using the '@all' p4 revision
-	specifier.
+	Import at most 'n' changes, rather than the entire range of
+	changes included in the given revision specifier. A typical
+	usage would be use '@all' as the revision specifier, but then
+	to use '--max-changes 1000' to import only the last 1000
+	revisions rather than the entire revision history.
+
+--changes-block-size <n>::
+	The internal block size to use when converting a revision
+	specifier such as '@all' into a list of specific change
+	numbers. Instead of using a single call to 'p4 changes' to
+	find the full list of changes for the conversion, there are a
+	sequence of calls to 'p4 changes -m', each of which requests
+	one block of changes of the given size. The default block size
+	is 500, which should usually be suitable.
 
 --keep-path::
 	The mapping of file names from the p4 depot path to Git, by

git-p4.py

@@ -740,17 +740,43 @@ def createOrUpdateBranchesFromOrigin(localRefPrefix = "refs/remotes/p4/", silent
 def originP4BranchesExist():
         return gitBranchExists("origin") or gitBranchExists("origin/p4") or gitBranchExists("origin/p4/master")
 
-def p4ChangesForPaths(depotPaths, changeRange):
+def p4ChangesForPaths(depotPaths, changeRange, block_size):
     assert depotPaths
-    cmd = ['changes']
-    for p in depotPaths:
-        cmd += ["%s...%s" % (p, changeRange)]
-    output = p4_read_pipe_lines(cmd)
+    assert block_size
+
+    # Parse the change range into start and end
+    if changeRange is None or changeRange == '':
+        changeStart = '@1'
+        changeEnd = '#head'
+    else:
+        parts = changeRange.split(',')
+        assert len(parts) == 2
+        changeStart = parts[0]
+        changeEnd = parts[1]
 
+    # Accumulate change numbers in a dictionary to avoid duplicates
     changes = {}
-    for line in output:
-        changeNum = int(line.split(" ")[1])
-        changes[changeNum] = True
+
+    for p in depotPaths:
+        # Retrieve changes a block at a time, to prevent running
+        # into a MaxScanRows error from the server.
+        start = changeStart
+        end = changeEnd
+        get_another_block = True
+        while get_another_block:
+            new_changes = []
+            cmd = ['changes']
+            cmd += ['-m', str(block_size)]
+            cmd += ["%s...%s,%s" % (p, start, end)]
+            for line in p4_read_pipe_lines(cmd):
+                changeNum = int(line.split(" ")[1])
+                new_changes.append(changeNum)
+                changes[changeNum] = True
+            if len(new_changes) == block_size:
+                get_another_block = True
+                end = '@' + str(min(new_changes))
+            else:
+                get_another_block = False
 
     changelist = changes.keys()
     changelist.sort()
@@ -1911,7 +1937,10 @@ def __init__(self):
                 optparse.make_option("--import-labels", dest="importLabels", action="store_true"),
                 optparse.make_option("--import-local", dest="importIntoRemotes", action="store_false",
                                      help="Import into refs/heads/ , not refs/remotes"),
-                optparse.make_option("--max-changes", dest="maxChanges"),
+                optparse.make_option("--max-changes", dest="maxChanges",
+                                     help="Maximum number of changes to import"),
+                optparse.make_option("--changes-block-size", dest="changes_block_size", type="int",
+                                     help="Internal block size to use when iteratively calling p4 changes"),
                 optparse.make_option("--keep-path", dest="keepRepoPath", action='store_true',
                                      help="Keep entire BRANCH/DIR/SUBDIR prefix during import"),
                 optparse.make_option("--use-client-spec", dest="useClientSpec", action='store_true',
@@ -1940,6 +1969,7 @@ def __init__(self):
         self.syncWithOrigin = True
         self.importIntoRemotes = True
         self.maxChanges = ""
+        self.changes_block_size = 500
         self.keepRepoPath = False
         self.depotPaths = None
         self.p4BranchesInGit = []
@@ -2586,7 +2616,7 @@ def importNewBranch(self, branch, maxChange):
         branchPrefix = self.depotPaths[0] + branch + "/"
         range = "@1,%s" % maxChange
         #print "prefix" + branchPrefix
-        changes = p4ChangesForPaths([branchPrefix], range)
+        changes = p4ChangesForPaths([branchPrefix], range, self.changes_block_size)
         if len(changes) <= 0:
             return False
         firstChange = changes[0]
@@ -3002,7 +3032,7 @@ def run(self, args):
                 if self.verbose:
                     print "Getting p4 changes for %s...%s" % (', '.join(self.depotPaths),
                                                               self.changeRange)
-                changes = p4ChangesForPaths(self.depotPaths, self.changeRange)
+                changes = p4ChangesForPaths(self.depotPaths, self.changeRange, self.changes_block_size)
 
                 if len(self.maxChanges) > 0:
                     changes = changes[:min(int(self.maxChanges), len(changes))]

t/t9818-git-p4-block.sh

@@ -0,0 +1,64 @@
+#!/bin/sh
+
+test_description='git p4 fetching changes in multiple blocks'
+
+. ./lib-git-p4.sh
+
+test_expect_success 'start p4d' '
+	start_p4d
+'
+
+test_expect_success 'Create a repo with ~100 changes' '
+	(
+		cd "$cli" &&
+		>file.txt &&
+		p4 add file.txt &&
+		p4 submit -d "Add file.txt" &&
+		for i in $(test_seq 0 9)
+		do
+			>outer$i.txt &&
+			p4 add outer$i.txt &&
+			p4 submit -d "Adding outer$i.txt" &&
+			for j in $(test_seq 0 9)
+			do
+				p4 edit file.txt &&
+				echo $i$j >file.txt &&
+				p4 submit -d "Commit $i$j" || exit
+			done || exit
+		done
+	)
+'
+
+test_expect_success 'Clone the repo' '
+	git p4 clone --dest="$git" --changes-block-size=10 --verbose //depot@all
+'
+
+test_expect_success 'All files are present' '
+	echo file.txt >expected &&
+	test_write_lines outer0.txt outer1.txt outer2.txt outer3.txt outer4.txt >>expected &&
+	test_write_lines outer5.txt outer6.txt outer7.txt outer8.txt outer9.txt >>expected &&
+	ls "$git" >current &&
+	test_cmp expected current
+'
+
+test_expect_success 'file.txt is correct' '
+	echo 99 >expected &&
+	test_cmp expected "$git/file.txt"
+'
+
+test_expect_success 'Correct number of commits' '
+	(cd "$git" && git log --oneline) >log &&
+	test_line_count = 111 log
+'
+
+test_expect_success 'Previous version of file.txt is correct' '
+	(cd "$git" && git checkout HEAD^^) &&
+	echo 97 >expected &&
+	test_cmp expected "$git/file.txt"
+'
+
+test_expect_success 'kill p4d' '
+	kill_p4d
+'
+
+test_done