From 1f861fa9f5cb3fe8a1d6cec35207a8da6d4df541 Mon Sep 17 00:00:00 2001 From: Daniel Nichter Date: Sun, 10 Jun 2012 12:41:24 -0400 Subject: [PATCH] Fix docs about skipping chunks with bad plans. --- bin/pt-online-schema-change | 9 +++++---- bin/pt-table-checksum | 9 +++++---- 2 files changed, 10 insertions(+), 8 deletions(-) diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change index 1c5793ed..c1cdcabd 100755 --- a/bin/pt-online-schema-change +++ b/bin/pt-online-schema-change @@ -7292,7 +7292,7 @@ the tool to run EXPLAIN before running queries that are meant to access a small amount of data, but which could access many rows if MySQL chooses a bad execution plan. These include the queries to determine chunk boundaries and the chunk queries themselves. If it appears that MySQL will use a bad query -execution plan, the tool will skip the table or the chunk of the table. +execution plan, the tool will skip the chunk of the table. The tool uses several heuristics to determine whether an execution plan is bad. The first is whether EXPLAIN reports that MySQL intends to use the desired index @@ -7305,9 +7305,10 @@ remembers the largest key_len seen, and skips chunks where MySQL reports that it will use a smaller prefix of the index. This heuristic can be understood as skipping chunks that have a worse execution plan than other chunks. -The tool prints a warning the first time a chunk is skipped due to a bad execution -plan in each table. Subsequent chunks are skipped silently, although you can see -the count of skipped chunks in the SKIPPED column in the tool's output. +The tool prints a warning the first time a chunk is skipped due to +a bad execution plan in each table. Subsequent chunks are skipped silently, +although you can see the count of skipped chunks in the SKIPPED column in +the tool's output. This option adds some setup work to each table and chunk. Although the work is not intrusive for MySQL, it results in more round-trips to the server, which diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum index 17b8e2a2..12b4b8a1 100755 --- a/bin/pt-table-checksum +++ b/bin/pt-table-checksum @@ -8109,7 +8109,7 @@ pt-table-checksum to run EXPLAIN before running queries that are meant to access a small amount of data, but which could access many rows if MySQL chooses a bad execution plan. These include the queries to determine chunk boundaries and the chunk queries themselves. If it appears that MySQL will use a bad query -execution plan, the tool will skip the table or the chunk of the table. +execution plan, the tool will skip the chunk of the table. The tool uses several heuristics to determine whether an execution plan is bad. The first is whether EXPLAIN reports that MySQL intends to use the desired index @@ -8122,9 +8122,10 @@ remembers the largest key_len seen, and skips chunks where MySQL reports that it will use a smaller prefix of the index. This heuristic can be understood as skipping chunks that have a worse execution plan than other chunks. -The tool prints a warning the first time a chunk is skipped due to a bad execution -plan in each table. Subsequent chunks are skipped silently, although you can see -the count of skipped chunks in the SKIPPED column in the tool's output. +The tool prints a warning the first time a chunk is skipped due to +a bad execution plan in each table. Subsequent chunks are skipped silently, +although you can see the count of skipped chunks in the SKIPPED column in +the tool's output. This option adds some setup work to each table and chunk. Although the work is not intrusive for MySQL, it results in more round-trips to the server, which