I would like temporary (let's say just for 1 sec) to increase the -lruskips to its maximal value (2147483647). Are there any negative effects I might cause?
Maybe it would be better to use the value that should be a bit less than 2147483647 looks? The -lruskips cuts LRU locks by (-lruskips + 1) times. I guess Progress reads the number of the block accesses ("Usect"?) stored in the pool of buffer headers and takes the modulo (-lruskips + 1) value. If the result is zero than the block is moved on LRU chain. The 2147483648 would be too large for a signed 4-byte integer. But the tests did not revealed the problems with this -lruskips value.
BTW, kbase incorrectly states that maximum is 2147483648:
Article: Why is a maximum value of 2GB stated in the OpenEdge documentation for the LRU force skips (-lruskips) parameter?
Thanks in advance,
George
I'd be interested in hearing what happens :)
And new tests did found some inconsistency. If I set the high value of the -lruskips online using promon and then return it back to zero the behaviour of Progress sessions will not be the same as just after db startup with -lruskips 0. I used promon itself to access the blocks. Any action in promon ("U"pdate, "S"ample, "Z"ero and even "R"epeat?!) reads the ACO object blocks - one block per data area including "Control Area". And, by the way, the queries of any VSTs do the same. It's VERY unfortunate that these blocks are on the LRU chain. So in sports db promon's actions will read 7 blocks (and will create 7 BHT and 7 LRU latch locks). We can create db accesses and check their latch locks without leaving the "Activity: Latch Counts" screen. After the changing the -lruskips forth and back these actions will not lock LRU latch anymore. Really it's excellent news! But I would like to understand if it's a real thing or just a "mirage". ;-)
What is "ACO"?
"Area Control Object" object block = bk_type 12 + objectId 0, block 3 in each area:
OBJBLK:
0040 totalBlocksOld: 0x%016x %d
hiWaterBlockOld: 0x%016x %d
chainFirst[FREECHN]: 0x%016I64x %I64u
0050 chainFirst[RMCHN]: 0x%016I64x %I64u
chainFirst[LOCKCHN]: 0x%016I64x %I64u
0060 numBlocksOnChainOld[FREECHN]: 0x%016x %d
numBlocksOnChainOld[RMCHN]: 0x%016x %d
numBlocksOnChainOld[LOCKCHN]: 0x%016x %d
0070 chainLast[FREECHN]: 0x%016I64x %I64u
chainLast[RMCHN]: 0x%016I64x %I64u
0080 chainLast[LOCKCHN]: 0x%016I64x %I64u
objectId: 0x%04hx %d
objectType: 0x%04hx %d
0090 serialNumber: 0x%016I64x %I64u
firstFreeCluster: 0x%016I64x %I64u
00A0 lastFreeCluster: 0x%016I64x %I64u
totalBlocks: 0x%016I64x %I64u
00B0 hiWaterBlock: 0x%016I64x %I64u
numBlocksOnChain[FREECHN]: 0x%016I64x %I64u
00C0 numBlocksOnChain[RMCHN]: 0x%016I64x %I64u
numBlocksOnChain[LOCKCHN]: 0x%016I64x %I64u
00D0 partitionId: 0x%04hx %d
Got it. I couldn't figure out the abbreviation -- but that makes sense.
The explanation found. New value of the -lruskips will be used after a block will be accessed N times where N is the previous value of the -lruskips. So if we will increase the -lruskips to 2 billions and then will change it back to 0 it will take a lot of time ("eternity") before previous value will "expire". The blocks that were not accessed while the -lruskips was set to 2 billions will use the current -lruskips value immidiately. Excellent! It's what I need. We can start db with -lruskips 2147483647 and then immidiately change it to the "working" value. The -lruskips 2147483647 will stay in use for the blocks accessed at db startup including the ACO blocks. Or increase the -lruskips at any time, take Z, U, L or R action in promon' screen and return the previous value of the -lruskips. It can be done almost instantly. The ACO blocks (and most likely only these blocks) will be "infected" by the maximum -lruskips value.
Tom, the trick can be useful for the scrips (like my dbmon) that use promon to gather db statistics as well as for 4GL programs that use VSTs (like ProTop). It makes them insensitive to the contention on LRU latch. I saw promon hung during the seconds when LRU latch was a bottleneck and in such cases a sampling interval missed the period with highest activity. I'm sure the same is true for VSTs.
The tests were re-done with a fresh mind. The trick is a bit harder than I thought yesterday: the -lruskips sets new "countdown" value in the buffer headers only when a buffer is accessed (obviously) and only when its current "countdown" counter is zero (what I missed yesterday).
proserve sports -lruskips 0
promon sports
Step 1: promon reads ACO blocks at its startup:
promon/R&D/debghb/6/1. Cache Entries
05/09/16 Status: Cache Entries
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips
33 64 1 139 O 0 L 4 0 0 0 0
34 64 6 824 O 0 L 1385 0 0 0 0
35 64 7 74 O 0 L 43 0 0 0 0
36 64 8 211 O 0 L 10 0 0 0 0
37 2 9 348 O 0 L 6 0 0 0 0
38 2 10 485 O 0 L 6 0 0 0 0
39 64 11 622 O 0 L 6 0 0 0 0
Step 2: Increase the -lruskips and access the ACO blocks.
4. Administrative Functions ...
4. Adjust Latch Options
8. Adjust LRU force skips: 100
U - Update activity counters (any "Activity" screen) in promon or read any VST table.
Look at the "Skips" coulmn.
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips 33 64 1 139 O 0 L 4 0 0 0 100 34 64 6 824 O 0 L 1385 0 0 0 100 35 64 7 74 O 0 L 43 0 0 0 100 36 64 8 211 O 0 L 10 0 0 0 100 37 2 9 348 O 0 L 6 0 0 0 100 38 2 10 485 O 0 L 6 0 0 0 100 39 64 11 622 O 0 L 6 0 0 0 100
Step 3: Access the ACO blocks again.
U - Update activity counters
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips 33 64 1 139 O 0 L 4 0 0 0 99 34 64 6 824 O 0 L 1385 0 0 0 99 35 64 7 74 O 0 L 43 0 0 0 99 36 64 8 211 O 0 L 10 0 0 0 99 37 2 9 348 O 0 L 6 0 0 0 99 38 2 10 485 O 0 L 6 0 0 0 99 39 64 11 622 O 0 L 6 0 0 0 99
Step 4: Increase the -lruskips to its maximum value and access the ACO blocks.
8. Adjust LRU force skips: 2147483647
U - Update activity counters
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips 33 64 1 139 O 0 L 4 0 0 0 98 34 64 6 824 O 0 L 1385 0 0 0 98 35 64 7 74 O 0 L 43 0 0 0 98 36 64 8 211 O 0 L 10 0 0 0 98 37 2 9 348 O 0 L 6 0 0 0 98 38 2 10 485 O 0 L 6 0 0 0 98 39 64 11 622 O 0 L 6 0 0 0 98
Step 5: Access the ACO blocks another 98 times
UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU... ;-)
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips 33 64 1 139 O 0 L 4 0 0 0 0 34 64 6 824 O 0 L 1385 0 0 0 0 35 64 7 74 O 0 L 43 0 0 0 0 36 64 8 211 O 0 L 10 0 0 0 0 37 2 9 348 O 0 L 6 0 0 0 0 38 2 10 485 O 0 L 6 0 0 0 0 39 64 11 622 O 0 L 6 0 0 0 0
Step 6: Access the ACO blocks just one more time:
Num DBKEY Area Hash T S Usect Flags Updctr Lsn Chkpnt Lru Skips 33 64 1 139 O 0 L 4 0 0 0 2147483647 34 64 6 824 O 0 L 1385 0 0 0 2147483647 35 64 7 74 O 0 L 43 0 0 0 2147483647 36 64 8 211 O 0 L 10 0 0 0 2147483647 37 2 9 348 O 0 L 6 0 0 0 2147483647 38 2 10 485 O 0 L 6 0 0 0 2147483647 39 64 11 622 O 0 L 6 0 0 0 2147483647
#------------------------------------------------------------------------------
LruShot()
{
# "Flu Shot": make ACO ("Area Control Object") Object Blocks insensitive to
# the contention on LRU latch. Promon will work even if LRU latch is locked.
# Script sets "Skips" value in Cache Entries (promon/R&D/debghb/6/1)
# to 2147483647 (a maximum value of the -lruskips). Access to these blocks
# will not acquire the LRU latch the next 2 billions times.
#
Db=$1
MaxSkips=2147483647
MinSkips=2000
# Do nothing if the current -lruskips is higher than MinSkips.
# Otherwise set it to MaxSkips for a short period of time.
# The higher the current lruskips the longer the script will work:
# Approximately 1 sec per 1000 skips.
PROSHUT=${PROSHUT-$DLC/bin/_mprshut}
# Get the current value of the -lruskips:
LruSkips=`
(echo "R&D" # Advanced options
echo "4" # 4. Administrative Functions ...
echo "4" # 4. Adjust Latch Options
# 4. Adjust LRU force skips: 0
) | \
$PROSHUT $Db -0 -NL 2>/dev/null | tr -d "\f" | \
awk '/Adjust LRU force skips:/ {print $NF}'
` # LruSkips
echo The current lruskips: $LruSkips
test $LruSkips -le $MinSkips && \
echo Reading ACO blocks in loop... && \
time \
(
# Set the -lruskips to MaxSkips:
echo "R&D" # Advanced options
echo "4" # 4. Administrative Functions ...
echo "4" # 4. Adjust Latch Options
echo "4" # 4. Adjust LRU force skips:
echo "$MaxSkips" # Enter new LRU force skips value
# Read ACO blocks = Update activity counters:
echo "T" # Return to the top level (main) menu.
echo "2" # 2. Activity Displays ...
echo "9" # 9. I/O Operations by File
MinSkips=$LruSkips
while [ $MinSkips -ge 0 ]
do
MinSkips=`expr $MinSkips - 1`
echo "U" # Update activity counters.
done
# Reset the -lruskips to its initial value:
echo "T" # Return to the top level (main) menu.
echo "4" # 4. Administrative Functions ...
echo "4" # 4. Adjust Latch Options
echo "4" # 4. Adjust LRU force skips:
echo $LruSkips # Enter new LRU force skips value
echo "X" # Exit from the OpenEdge Monitor utility.
) | \
$PROSHUT $Db -0 -NL 2>/dev/null 1>&2
} # LruShot
#------------------------------------------------------------------------------
LruShot sports